Patent Publication Number: US-2005117643-A1

Title: Moving image transferring system, moving image encoding apparatus, moving image decoding apparatus, and moving image transferring program

Description:
TECHNICAL FIELD  
      The present invention relates to a moving picture transmission system for encoding and sending moving picture data and receiving and decoding the encoded data that has been sent, and more particularly to a moving picture transmission system, a moving picture encoding apparatus, a moving picture decoding apparatus, and a moving picture transmission program for minimizing corruptions of decoded images which are caused by transmission errors of encoded data.  
     BACKGROUND ART  
      In recent years, processes for efficiently transmitting moving picture data by encoding the moving picture data according to high efficient compression encoding based on interframe prediction are widely used in the art. Typical examples of moving picture compression encoding include MPEG (Moving Picture Expert Group)-1, MPEG-2, MPEG-4, etc.  
      According to these processes, an encoded image is predicted from temporally preceding and following frames by a process such as motion compensation or the like, and obtained interframe prediction parameters and residual image data are encoded to reduce the amount of information of moving picture data that are highly correlated temporally. Furthermore, the residual image data are efficiently compressed by conversion encoding or quantization to make it possible to transmit moving picture data of good image quality in a small transmission band.  
      According to the conventional moving picture data transmission processes, however, if the transmission data suffer long burst errors or transmission packet dropouts which cannot be restored even with an error correcting code, then the recipient is unable to decode the image data of frames suffering such errors or dropouts.  
      Countermeasures that can be taken by the recipient against the above problems include an error concealment process for generating image data which contain less noticeable errors from properly decoded image data of temporally preceding and following frames and properly decoded surrounding image data within the same frame. However, it is impossible for the error concealment process to remove decoded image corruptions. Another problem of this process is that since it employs interframe prediction, an image corruption which has occurred is propagated to a succeeding frame.  
     DISCLOSURE OF THE INVENTION  
      The present invention has been made in view of the above drawbacks. It is a first object of the present invention to provide a moving picture transmission system, a moving picture encoding apparatus, a moving picture decoding apparatus, and a moving picture transmission program which make it possible to minimize corruptions of decoded images at a recipient site which are caused by transmission errors of encoded data.  
      A second object of the present invention to provide a moving picture transmission system, a moving picture encoding apparatus, a moving picture decoding apparatus, and a moving picture transmission program which achieve the first object while reducing any increase in the transmission band that is required.  
      A third object of the present invention to provide a moving picture transmission system, a moving picture encoding apparatus, a moving picture decoding apparatus, and a moving picture transmission program which achieve the first object while preventing the amount of processing required to decode compression-encoded data from increasing.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system comprising a transmission side sending encoded moving picture data and one or plural reception sides decoding the moving picture data, wherein the transmission side sends a plurality of encoded data comprising primary encoded data produced by compressing input moving picture frames using interframe prediction, and one or plural encoded data produced by compressing the input frames at one or plural compression ratios, which are higher than the compression ratio of the primary encoded data, using interframe prediction referring to picture frames obtained by decoding the primary encoded data; and each of the reception sides selects one of encoded data with frame-by-frame selection from the plurality of encoded data received by the reception side without error, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system comprising a transmission side sending encoded moving picture data and one or plural reception sides decoding the moving picture data, wherein the transmission side sends a plurality of encoded data comprising primary packet data produced by compressing input moving picture frames into one or plural packets using interframe prediction, and one or plural encoded packet data produced by compressing the image area which is contained in each packet of the as primary packet data, into one or plural packet data at one or plural compression ratios, which are higher than the compression ratio of the primary packet data, using interframe prediction referring to picture frames obtained by decoding the primary encoded data; and each of the reception sides selects one of encoded data with packet-by-packet selection from the plurality of encoded packet data received by the reception side without error, and decode the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system comprising a transmission side sending encoded moving picture data and one or plural reception sides decoding the moving picture data, wherein the transmission side sends a plurality of encoded data comprising primary encoded data produced by compressing input moving picture frames using interframe prediction, and one or plural encoded data produced by compressing the input frames at one or plural compression ratios, which are higher than the compression ratio of the primary encoded data, using interframe prediction referring to the same picture frames as the frames referred to in the interframe prediction of the primary encoded data; and each of the reception sides selects one of encoded data with frame-by-frame selection from the plurality of encoded data received by the reception side without error, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system comprising a transmission side sending encoded moving picture data and one or plural reception sides decoding the moving picture data, wherein the transmission side sends a plurality of encoded data comprising primary encoded data produced by compressing input moving picture frames using interframe prediction, and one or plural encoded data produced by compressing the input frames at one or plural compression ratios, which are higher than the compression ratio of said primary encoded data, by reusing the prediction parameters and the residual image data which are obtained in the interframe prediction of the primary encoded data; and each of the reception sides selects one of encoded data with frame-by-frame selection from the plurality of encoded data received by the reception side without error, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system comprising a transmission side sending encoded moving picture data and one or plural reception sides decoding the moving picture data, wherein the transmission side sends a plurality of encoded data comprising primary packet data produced by compressing input moving picture frames into one or plural packets using interframe prediction, and one or plural encoded packet data produced by compressing the image area, which is contained in each packet of the primary packet data, into one or plural packet data at one or plural compression ratios, which are higher than the compression ratio of the primary packet data, by reusing the prediction parameters and the residual image data, which are obtained by the interframe prediction of the primary packet data; and each of the reception sides selects one of encoded data with packet-by-packet selection from the plurality of encoded data received by the reception side without error, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system comprising a transmission side sending encoded moving picture data and one or plural reception sides decoding the moving picture data, wherein the transmission side sends a plurality of encoded data comprising primary packet data produced by compressing input moving picture frames into one or plural packets using interframe prediction, and one or plural encoded packet data produced by compressing the image area, which is contained in each packet of said primary packet data, into one or plural packet data at one or plural compression ratios, which are higher than the compression ratio of the or the same as primary packet data, using interframe prediction referring to the same picture frames as the frames referred to in the interframe prediction of the primary packet data; and each of the reception sides selects one of encoded data with packet-by-packet selection from the plurality of encoded data received by the reception side without error, and decodes the selected encoded data.  
      The transmission side may send a plurality of encoded data comprising all compression-encoded data or encoded data of selected frames.  
      The transmission side may send a plurality of packet data comprising all compression-encoded packet data or selected packet data.  
      Each one of the reception sides selects the encoded data having the lowest compression ratio from the plurality of encoded data received without error, and decode the selected encoded data.  
      The transmission side may assign priority orders to the plurality of encoded data subject to a predetermined assignment rule, and each one of the reception sides selects encoded data having the highest priority order from the plurality of encoded data received by the reception side without error and decodes the selected encoded data.  
      The transmission side may multiplex the plurality of encoded data with time differences added therebetween and sends the multiplexed encoded data, and the reception side may demultiplex the multiplexed and sent encoded data into a plurality of encoded data.  
      The moving picture transmission system may comprise a moving picture encoding apparatus as the transmission side and a moving picture decoding apparatus as the reception side, the moving picture encoding apparatus having: a plurality of encoding means for compressing input moving picture frames into a plurality of encoded data having different compression ratios and sending the encoded data, the moving picture decoding apparatus having: a plurality of encoded-data-receiving means for receiving the plurality of encoded data which have been sent and detecting bit errors or packet losses of the received encoded data; a selecting mean for selecting either one encoded data from the encoded data which have been received free of bit errors or packet losses by the encoded data-receiving-means; and a decoding mean for decoding the encoded data selected by the selecting mean.  
      The transmission side may have delay-adding means for delaying part of the encoded data to add the time differences between the plurality of encoded data, and multiplexing means for multiplexing the plurality of encoded data with the time differences added therebetween and sending the multiplexed data, and each of the reception sides has demultiplexing means for demultiplexing the multiplexed and sent data into a plurality of encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system for transmitting moving picture data which have been compressed using interframe prediction from a transmission side to one or plural reception sides, where N represents an integer of 2 or greater, wherein: the transmission side comprises: first moving-picture-encoding/sending means for compressing input moving picture frames using interframe prediction, and sending obtained encoded data with predetermined transmitting means; and second through Nth (N-1) moving-picture-encoding/sending means for encoding at least part of the frames, which are encoded by the first moving-picture-encoding/sending means, at one or plural compression ratios, which are higher than the compression ratio of the first moving-picture-encoding/sending means, using reference frame image used in the interframe prediction performed on the frames by the first moving-picture-encoding/sending means, and sending obtained encoded data; and each one of the reception sides comprises: N encoded data-receiving means for detecting errors or dropouts in frames of the received moving-picture-encoded data; and moving-picture-decoding means for selecting the moving-picture-encoded data having the lowest compression ratio with frame-by-frame selection from encoded data which have been received free of transmission errors and dropouts by the N encoded-data-receiving means, and decoding the selected moving-picture-encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system for transmitting moving picture data which have been compressed using interframe prediction from a transmission side to one or plural reception sides, where N represents an integer of 2 or greater, wherein: the transmission side comprises: first moving-picture-encoding/sending means for compressing input moving picture frames into one or plural packet data using interframe prediction, and sending the obtained one or plural packet data with predetermined transmitting means; and second through Nth (N-1) moving-picture-encoding/sending means for encoding each image area, which is encoded into a packet by the first moving-picture-encoding/sending means, into packet data at one or plural compression ratios, which are higher than the compression ratio of the first moving-picture-encoding/sending means, referring to reference frame images used in the interframe prediction performed on the image area by the first-moving-picture-encoding/sending means, and sending the obtained packet data; and each one of the reception sides comprises: N encoded-data-receiving means for detecting errors or dropouts in encoded packet data of the received moving-picture-encoded data; and moving-picture-decoding means for selecting the encoded packet data having the lowest compression ratio with packet-by-packet selection from packet data which have been received free of transmission errors and dropouts by the N encoded-data-receiving means, and decoding the selected encoded packet data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system for transmitting moving picture data which have been compressed using interframe prediction from a transmission side to one or plural reception sides, where N represents an integer of 2 or greater, wherein: the transmission side comprises: first moving-picture-encoding/sending means for compression-encoding input moving picture frames according to interframe prediction, and sending obtained encoded data with predetermined transmitting means; and second through Nth (N-1) moving picture encoding/sending means for encoding at least part of the frames, which are encoded by the first moving-picture-encoding/sending means, at one or plural compression ratios, which are higher than the compression ratio of the first moving-picture-encoding/sending means, reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction performed on the frames by the first moving-picture-encoding/sending means, and sending obtained encoded data; and each one of the reception sides comprises: N encoded data-receiving means for detecting errors or dropouts in frames of the received moving-picture-encoded data; and moving-picture-decoding means for selecting the moving-picture-encoded data having the lowest compression ratio with frame-by-frame selection from encoded data which have been received free of transmission errors and dropouts by said encoded-data-receiving means, and decoding the selected moving-picture-encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system for transmitting moving picture data which have been compressed using interframe prediction from a transmission side to one or plural reception sides, where N represents an integer of 2 or greater, wherein: the transmission side comprises: first moving-picture-encoding/sending means for compressing input moving picture frames into one or plural packet data using interframe prediction, and sending the obtained encoded packet data with predetermined transmitting means; and second through Nth (N-1) moving-picture-encoding/sending means for encoding each image area, which is encoded into a pecket by said first moving-picture-encoding/sending means, into packet data at one or plural compression ratios, which are higher than the compression ratio of the first moving-picture-encoding/sending means, reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction performed on the image area by said first moving-picture-encoding/sending means, and sending the obtained packet data; and each one of the reception sides comprises: N encoded data-receiving means for detecting errors or dropouts in packet data of the received moving-picture-encoded data; and moving-picture-decoding means for selecting the encoded packet data having the lowest compression ratio with packet-by-packet selection from packet data which have been received free of transmission errors and dropouts by said N encoded-data-receiving means, and decoding the selected encoded packet data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture encoding apparatus for compressing moving picture data and sending the encoded data to one or plural moving-picture-decoding apparatuses, wherein the moving-picture-encoding apparatus sends a plurality of encoded data comprising primary encoded data produced by compressing frames of input moving picture data based on interframe prediction, and encoded data produced by compressing the encoded frames at one or plural compression ratios, which are higher than the or the same as primary encoded data, based on interframe prediction using reference frame images used in the interframe prediction of the primary encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture encoding apparatus for compressing moving picture data and sending the encoded data to one or plural moving-picture-decoding apparatuses, wherein the moving-picture-encoding apparatus sends a plurality of encoded data comprising primary packet data produced by compressing frames of input moving picture data based on interframe prediction, and packet data produced by compressing each image area, which is encoded into a packet of the primary packet data, at one or plural compression ratios, which are higher than the primary packet data, according to interframe prediction using reference frame images used in the interframe prediction of the primary encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture encoding apparatus for compressing moving picture data and sending the encoded data to one or plural moving-picture-decoding apparatuses, wherein the moving-picture-encoding apparatus sends a plurality of encoded data comprising primary encoded data produced by compressing frames of input moving picture data based on interframe prediction, and encoded data produced by compressing at least part of the encoded frames at one or plural compression ratios, which are higher than the primary encoded data, by reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction of the primary encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture encoding apparatus for compressing moving picture data and sending the encoded data to one or plural moving-picture-decoding apparatuses, wherein the moving-picture-encoding apparatus sends a plurality of encoded data comprising primary packet data produced by compressing frames of input moving picture data based on interframe prediction, and packet data produced by compressing each image area, which is encoded into a packet of the primary packet data, at one or plural compression ratios which are higher than the primary packet data, by reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction of the primary packet data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture decoding apparatus for receiving data produced by compressing moving picture data from a moving-picture-encoding apparatus and decoding the received data, wherein the moving-picture-decoding apparatus receives a plurality of encoded data comprising primary encoded data produced by compressing frames of input moving picture data based on interframe prediction, and encoded data produced by compressing the encoded frames at one or plural compression ratios, which are higher than the primary encoded data based on interframe prediction using reference frame images used in the interframe prediction of the primary encoded data, selects the encoded data having the lowest compression ratio with frame-by-frame selection from the encoded data free of bit errors or packet losses of the received encoded data, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture decoding apparatus for receiving data produced by compressing moving picture data from a moving-picture-encoding apparatus and decoding the received data, wherein the moving-picture-decoding apparatus receives a plurality of encoded data comprising primary packet data produced by compressing frames of input moving picture data based on interframe prediction, and packet data produced by compressing each image area, which is encoded into a packet of said primary packet data, at one or plural compression ratios, which are higher than the or the same as primary packet data, according to interframe prediction using reference frame images used in the interframe prediction of the primary encoded data, selects the encoded packet data having the lowest compression ratio with packet-by-packet selection from the encoded data free of transmission errors and dropouts of the received encoded data, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture decoding apparatus for receiving data produced by compressing moving picture data from a moving-picture-encoding apparatus and decoding the received data, wherein the moving-picture-decoding apparatus receives a plurality of encoded data comprising primary encoded data produced by compressing frames of input moving picture data based on interframe prediction, and encoded data produced by compressing at least part of the encoded frames at one or plural compression ratios, which are higher than the or the same as primary encoded data, by reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction of the primary encoded data, selects the encoded data having the lowest compression ratio with frame-by-frame selection from the encoded data free of bit errors or packet losses of the received encoded data, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture decoding apparatus for receiving data produced by compressing moving picture data from a moving-picture-encoding apparatus and decoding the received data, wherein the moving-picture-decoding apparatus receives a plurality of encoded data comprising primary packet data produced by compressing frames of input moving picture data based on interframe prediction, and packet data produced by compressing each image area, which is encoded into a packet of the primary packet data, at one or plural compression ratios, which are higher than the or the same as primary packet data, by reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction of the primary packet data, selects the encoded packet data having the lowest compression ratio with packet-by-packet selection from the encoded data free of transmission errors and dropouts of the received encoded data, and decodes the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system having a moving picture transmission program for enabling a computer processor to encode moving picture data and send the encoded data at a transmission side, and enabling a computer processor to receive and decode the encoded data at a reception side, wherein the moving picture transmission program enables the computer processor at the transmission side to send a plurality of encoded data comprising primary encoded data produced by compressing frames of input moving picture data based on interframe prediction, and encoded data produced by compressing the encoded frames at one or plural compression ratios, which are higher than the primary encoded data based on interframe prediction using reference frame images used in the interframe prediction of the primary encoded data, and enables the computer processor at the reception side to select the encoded data having the lowest compression ratio with frame-by-frame selection from the plurality of properly received encoded data and decode the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system having a moving picture transmission program for enabling a computer processor to encode moving picture data and send the encoded data at a transmission side, and enabling a computer processor to receive and decode the encoded data at a reception side, wherein the moving picture transmission program enables the computer processor at the transmission side to send a plurality of encoded data comprising primary packet data produced by compressing frames of input moving picture data based on interframe prediction, and packet data produced by compressing each image area, which is encoded into a packet of the primary packet data, at one or plural compression ratios, which are higher than the or the same as primary packet data, according to interframe prediction using reference frame images used in the interframe prediction of the primary encoded data, and enables the computer processor at the reception side to select the encoded data having the lowest compression ratio with packet-by-packet selection from the plurality of properly received encoded data and decode the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system having a moving picture transmission program for enabling a computer processor to encode moving picture data and send the encoded data at a transmission side, and enabling a computer processor to receive and decode the encoded data at a reception side, wherein the moving picture transmission program enables the computer processor at the transmission side to send a plurality of encoded data comprising primary encoded data produced by compressing frames of input moving picture data based on interframe prediction, and encoded data produced by compressing at least part of the encoded frames at one or plural compression ratios, which are higher than the primary encoded data, by reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction of the primary encoded data, and enables the computer processor at the reception side to select the encoded data having the lowest compression ratio with frame-by-frame selection from the plurality of properly received encoded data and decode the selected encoded data.  
      To achieve the above objects, there is provided in accordance with the present invention a moving picture transmission system having a moving picture transmission program for enabling a computer processor to encode moving picture data and send the encoded data at a transmission side, and enabling a computer processor to receive and decode the encoded data at a reception side, wherein the moving picture transmission program enables the computer processor at the transmission side to send a plurality of encoded data comprising primary packet data produced by compressing frames of input moving picture data based on interframe prediction, and packet data produced by compressing each image area, which is encoded into a packet of the primary packet data, at one or plural compression ratios, which are higher than the or the same as primary packet data, according to interframe prediction, by reusing interframe prediction parameters and residual image data which are obtained in the interframe prediction of the primary packet data, and enables the computer processor at the reception side to select the encoded data having the lowest compression ratio with packet-by-packet selection from the plurality of properly received encoded data and decode the selected encoded data.  
      According to the present invention, as described above, at a transmission side, moving picture data are compressing into primary encoded data, encoded frames are encoded into a plurality of encoded data using interframe prediction parameters and residual image data or a reference frame image obtained in the encoding of the frame, and the encoded data are sent to one or plural reception sides. At the reception side, encoded data having the lowest compression ratio and high image quality are selected in frames or packets from encoded data that are received normally by the reception side, and the selected encoded data are decoded. Therefore, even if a transmission path that is of low reliability, tending to cause transmission errors and packet errors of highly burst nature, is employed, the probability that both all the encoded data are transmitted in error is reduced, making it possible to prevent decoded images from suffering significant corruptions.  
      According to the present invention, furthermore, encoded data other than primary encoded data of a plurality of encoded data are encoded at a compression ratio which is higher than the primary encoded data, and the encoded data other than the primary encoded data can be encoded with respect to only part of a frame or an image area for which the primary encoded data have been encoded. Consequently, an increase caused in the transmission rate when the plural encoded data are sent may be reduced.  
      According to the present invention, furthermore, the transmission side generates encoded data containing the same frame or the same image area, and the reception side selects encoded data in frames or packets from a plurality of encoded data that are received and decodes the selected encoded data. Therefore, the reception side is not required to decode the plurality of received encoded data for the purpose of decoding the same frame or the same image area, making it possible to reduce an increase in the amount of calculations needed by the reception side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram showing an arrangement of a moving picture transmission system which realizes a moving picture transmission process according to a first embodiment of the present invention;  
       FIG. 2  is a block diagram showing an arrangement of a moving picture encoding apparatus according to the first embodiment of the present invention;  
       FIG. 3  is a block diagram showing an arrangement of a moving picture decoding apparatus according to the first embodiment of the present invention;  
       FIG. 4  is a flowchart showing an encoded data reconstructing sequence in the moving picture decoding apparatus according to the first embodiment of the present invention;  
       FIG. 5  is a flowchart showing an encoded data reconstructing sequence that is carried out if three encoded packet data are transmitted to the moving picture decoding apparatus in the first embodiment;  
       FIG. 6  is a block diagram showing an arrangement of a moving picture transmission system which realizes a moving picture encoded data packet transmission process according to a second embodiment of the present invention;  
       FIG. 7  is a flowchart showing an encoded data reconstructing sequence in a moving picture decoding apparatus according to a third embodiment of the present invention;  
       FIG. 8  is a flowchart showing an encoded data reconstructing sequence that is carried out if three encoded packet data are transmitted to the moving picture decoding apparatus in the third embodiment; and  FIG. 9  is a diagram showing an arrangement of a moving picture encoding apparatus according to a fourth embodiment of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Preferred embodiments of the present invention will be described in detail with reference to the drawings.  
     1ST EMBODIMENT  
      A moving picture transmission system according to a first embodiment of the present invention will be described in detail below with reference to the drawings.  FIG. 1  shows an overall arrangement of the moving picture transmission system according to the first embodiment.  
      As shown in  FIG. 1 , the moving picture transmission system according to the present embodiment comprises moving picture encoding apparatus  100  for encoding moving picture data, moving picture decoding apparatus  200 , and transmission path  300  for transmitting encoded moving picture data from moving picture encoding apparatus  100  to moving picture decoding apparatus  200 . In  FIG. 1 , N is an integer of 2 or greater, representing the number of encoded data sent from moving picture encoding apparatus  100 .  
      Moving picture encoding apparatus  100  is supplied with frames of moving picture data, encodes the supplied moving picture data into N encoded data, and sends the encoded data as 1st through Nth moving picture encoded packet data.  
      As shown in  FIG. 1 , moving picture encoding apparatus  100  has first through Nth N moving picture encoder/senders  101 - 1  through  101 -N. First moving picture encoder/sender  101 - 1  encodes the frames of moving picture data supplied to moving picture encoding apparatus  100  based on interframe prediction according to a predetermined compression encoding process, and sends the encoded data to moving picture decoding apparatus  200 .  
      Second through Nth N moving picture encoder/senders  101 - 2  through  101 -N encode all or part of frames encoded by first moving picture encoder/sender  101 - 1  at a compression ratio higher than first moving picture encoder/sender  101 - 1  using interframe prediction parameters and residual image data that are obtained by the interframe prediction performed by the first moving picture encoder/sender on those frames.  
      As described above, the compression ratio for encoding frames with second through Nth N moving picture encoder/senders  101 - 2  through  101 -N is higher than the compression ratio of first moving picture encoder/sender  101 - 1 . Second through Nth N moving picture encoder/senders  101 - 2  through  101 -N may have respective different compression ratios or the same compression ratio.  
      Moving picture decoding apparatus  200  receives and decodes the N encoded data sent from moving picture encoding apparatus  100  into moving picture data. As shown in  FIG. 1 , moving picture decoding apparatus  200  comprises first through Nth encoded data receivers  201 - 1  through  201 -N for receiving the encoded data sent from first through Nth N moving picture encoder/senders  101 - 1  through  101 -N of moving picture encoding apparatus  100 , encoded data reconstructor  202 , and moving picture data decoder  203 .  
      Encoded data reconstructor  202  selects one encoded data having the lowest compression ratio as encoded data to be decoded, from a maximum of N encoded data free of transmission errors and dropouts received by first through Nth encoded data receivers  201 - 1  through  201 -N.  
      Moving picture data decoder  203  decodes encoded data output from encoded data reconstructor  202  into moving picture data.  
      Details of the moving picture encoder/senders of moving picture encoding apparatus  100  are shown in  FIG. 2 . In  FIG. 2 , the number N of encoded data output by the apparatus is illustrated as “2” for the sake of brevity.  
      First moving picture encoder/sender  101 - 1  shown in  FIG. 2  has frame scanner  111  for rearranging supplied frames of moving picture data into an order to be encoded, interframe predictor  112  for performing interframe prediction on an image input from frame scanner  111  based on one or more decoded images stored in reference frame storage memory  119 , residual calculator  113  for subtracting a prediction image obtained by interframe predictor  112  from the input frame image to calculate a residual, first residual compression encoder  114 - 1  for compression-encoding the residual image obtained by residual calculator  113  according to a predetermined process, and first encoded packet generator  115 - 1  for variable-length-encoding the interframe predictive parameters obtained by interframe predictor  112  and the compressed data of the residual image obtained by first residual compression encoder  114 - 1  into a bit string and outputting the bit string in packets.  
      First moving picture encoder/sender  101 - 1  also has first packet error detecting code-frame/packet identification number adder  116 - 1  for adding an error detecting code and frame/packet identification numbers in order for a receiving apparatus to detect transmission errors and packet losses of the encoded packet data output by first encoded packet generator  115 - 1 , residual decoder  117  for determining decoded data of the residual encoded by first residual compression encoder  114 - 1 , decoded image calculator  118  for adding the prediction image generated by interframe predictor  112  and the residual decoded by residual decoder  117  into a decoded image, and reference frame storage memory  119  for storing decoded images in preparation for the encoding of a next frame.  
      First moving picture encoder/sender  101 - 1  according to the present embodiment operates with the above processing components.  
      Second moving picture encoder/sender  101 - 2  shown in  FIG. 2  has second residual compression encoder  114 - 2  for encoding the residual image obtained by residual calculator  113  at a compression ratio higher than the compression ratio of first residual compression encoder  114 - 1 , second encoded packet generator  115 - 2  for variable-length-encoding the interframe predictive parameters obtained by interframe predictor  112  and the compressed data of the residual obtained by second residual compression encoder  114 - 2  into a bit string and outputting the bit string in packets, and second moving picture encoder/sender  101 - 2  also has second packet error detecting code-frame/packet identification number adder  116 - 2  for adding an error detecting code and frame/packet identification numbers in order for the receiving apparatus to detect transmission errors and packet losses of the compressed packet data output by second encoded packet generator  115 - 2 .  
      Second moving picture encode data are obtained when the above processing components operate, and sent in packets by a predetermined sending means. Second moving picture encoder/sender  101 - 2  of moving picture encoding apparatus  100  according to the present embodiment operates with the above processing components.  
      In  FIG. 2 , only second moving picture encoder/sender  101 - 2  is shown. However, third through Nth moving picture encoder/senders  101 - 3  through  101 -N shown in  FIG. 1  are of the same arrangement as second moving picture encoder/sender  101 - 2 .  
      The arrangement and operation of moving picture encoding apparatus  100  according to the present embodiment have been described above.  
      In the present embodiment, first packet error detecting code-frame/packet identification number adder  116 - 1  is provided for adding an error detecting code and frame/packet identification numbers to the first encoded packet data output from first encoded packet generator  115 - 1 . However, any other processes may be employed if they enable moving picture decoding apparatus  200  to detect transmission errors and packet losses of the encoded packet data that are sent. For example, if the first encoded packet transmission path has a mechanism for detecting transmission errors, then there is no need for first packet error detecting code-frame/packet identification number adder  116 - 1  to add an error detecting code. According to another example, if the encoded data output from first encoded packet generator  115 - 1  contain information for identifying frames and packets, then there is no need for first packet error detecting code-frame/packet identification number adder  116 - 1  to add frame/packet identification numbers.  
      Similarly, second packet error detecting code-frame/packet identification number adder  116 - 2  is provided for adding an error detecting code and frame/packet identification numbers to the second encoded packet data. However, any other processes may be employed if they enable moving picture decoding apparatus  200  to detect transmission errors and packet losses of the encoded packet data that are sent.  
      In a preferred specific example of the first embodiment described above, the moving picture encoding apparatus is connected to an Internet communication network, compresses a moving picture input by a camera or the like into encoded data according to the MPEG-4 Visual process, and transmits the encoded data using the UDP/IP protocol. Interframe predictor  112  performs interframe prediction based on motion compensation. First residual compression encoder  114 - 1  and second residual compression encoder  114 - 2  perform a compression process based on two-dimensional discrete cosine transform (2D-DCT) and quantization.  
      Second residual compression encoder  114 - 2  compresses image data such that the compression ratio of the second encoded data is higher than the compression ratio of the first encoded data, according to a process for quantizing 2D-DCT coefficients using quantization parameters greater than first residual compression encoder  114 - 1  or a process of adaptively cutting off high-order 2D-DCT.  
      Residual decoder  117  performs inverse quantization and two-dimensional inverse discrete cosine transform (2D-IDCT). First encoded packet generator  115 - 1  encodes quantization DCT coefficients output from first residual compression encoder  114 - 1  and motion vectors output from interframe predictor  112 , according to the syntax prescribed by the MPEG-4 Visual process.  
      Similarly, second encoded packet generator  115 - 2  encodes quantization DCT coefficients output from second residual compression encoder  114 - 2  and motion vectors output from interframe predictor  112 , according to the syntax prescribed by the MPEG-4 Visual process. First packet error detecting code-frame/packet identification number adder  116 - 1  and second packet error detecting code-frame/packet identification number adder  116 - 2  generate a UDP datagram including a check sum for detecting an error, and sends the generated UDP datagram to the moving picture decoding apparatus connected to the Internet.  
       FIG. 3  shows a detailed arrangement of moving picture decoding apparatus  200  according to the first embodiment.  
      First encoded data receiver  201 - 1  shown in  FIG. 3  has first packet reception buffer  211 - 1  for receiving first encoded packet data sent from the encoding apparatus, first encoded data extractor  212 - 1  for extracting moving picture encoded data from the packet data received by first packet reception buffer  211 - 1 , and first packet error detector/packet loss detector  213 - 1  for detecting bit errors and packet losses that have occurred when the first encoded packet data are transmitted.  
      First encoded data receiver  201 - 1  operates with the processors of the above components.  
      Similarly, second encoded data receiver  201 - 2  shown in  FIG. 3  has second packet reception buffer  211 - 2  for receiving second encoded packet data sent from the encoding apparatus, second encoded data extractor  212 - 2  for extracting moving picture encoded data from the packet data received by second packet reception buffer  211 - 2 , and second packet error detector/packet loss detector  213 - 2  for detecting bit errors and packet losses that have occurred when the second encoded packet data are transmitted.  
      Second encoded data receiver  201 - 2  operates with the processors of the above components.  
      Encoded data reconstructor  202  reconstructs the two encoded data sent from the encoding apparatus into single encoded data according to the results of errors and packet losses detected by first packet error detector/packet loss detector  213 - 1  and second packet error detector/packet loss detector  213 - 2 .  
      Moving picture data decoder  203  shown in  FIG. 3  comprises variable-length decoder  251  for variable-length-decoding the encoded data reconstructed by encoded data reconstructor  202 , residual decoder  252 , interframe prediction image generator  253 , decoded image calculator  254  for adding a residual produced by residual decoder  252  and a prediction image produced by interframe prediction image generator  253  to determine a decoded image, reference frame storage memory  255  for storing decoded image data produced by decoded image calculator  254 , which is to be used in decoding a following frame, and frame scanner  256  for rearranging and outputting decoded images in an order to be reproduced.  
      Moving picture data decoder  203  of moving picture decoding apparatus  200  operates with the processors of the above components to produce moving picture data transmitted from moving picture encoding apparatus  100 .  
      An encoded data reconstructing sequence of encoded data reconstructor  202  according to the present embodiment will be described below with reference to a flowchart shown in  FIG. 4 . The sequence shown in  FIG. 4  represents a process of reconstructing encoded data of an nth frame where n is an integer.  
      In step S 401 , control waits until a time which is the sum of a time when all encoded data of the nth frame are to arrive at first packet reception buffer  211 - 1  and second packet reception buffer  211 - 2  and a predetermined allowable maximum delay time. Then, control goes to step S 402 .  
      In step S 402 , the following branching process is performed depending on the results of errors and packet losses detected by first packet error detector/packet loss detector  213 - 1 : If all encoded data of the nth frame are received by first packet reception buffer  211 - 1  and no error is detected in the data, then control goes to step S 403 . Otherwise, control goes to step S 404 .  
      In step S 403 , the encoded data of the nth frame output from first encoded data extractor  212 - 1  are transferred as encoded data to be decoded to variable-length decoder  251 . The, the encoded data reconstructing process is ended.  
      In step S 404 , the following branching process is performed depending on the results of errors and packet losses detected by second packet error detector/packet loss detector  213 - 2 : If all encoded data of the nth frame are received by second packet reception buffer  211 - 2  and no error is detected in the data, then control goes to step S 405 . Otherwise, control goes to step S 406 .  
      In step S 405 , the encoded data of the nth frame output from second encoded data extractor  212 - 2  are transferred as encoded data to be decoded to variable-length decoder  251 . The, the encoded data reconstructing process is ended.  
      Control proceeds to step S 406  when the encoded data of the nth frame cannot be received free of bit errors and packet losses by either one of first and second packet reception buffers  211 - 1 ,  211 - 2 .  
      In step S 406 , therefore, a concealment process for making less visible decoded image corruptions due to reception errors is carried out by an appropriate method.  
      For example, a command is sent to moving picture data decoder  203  to use a decoded image of a preceding (n-1)th frame as a decoded image of the nth frame.  
      Alternatively, processes to be described below may be employed.  
      If some of the encoded data of the nth frame are received by first packet reception buffer  211 - 1 , then the received encoded data are used for decoding the nth frame. If no encoded data at all are received by first packet reception buffer  211 - 1  and some of the encoded data of the nth frame are received by second packet reception buffer  211 - 2 , then the encoded data received by the second packet reception buffer are used for decoding the nth frame. If no encoded data of the nth frame at all are received by both the first and second packet reception buffers, then a decoded image of a preceding (n-1)th frame is output.  
      After the above concealment process is performed in step S 406 , the encoded data reconstructing process for the nth frame is ended.  
      The encoded data reconstructing process carried out by encoded data reconstructor  202  has been described above.  
       FIG. 4  illustrates the operation of encoded data reconstructor  202  where, as shown in  FIGS. 2 and 3 , N shown in  FIG. 1  is “2”, moving picture encoding apparatus  100  has first moving picture encoder/sender  101 - 1  and second moving picture encoder/sender  101 - 2 , and moving picture decoding apparatus  200  has first encoded data receiver  201 - 1  and second encoded data receiver  201 - 2 .  
      If N shown in  FIG. 1  is “3” and three or more encoded data are transmitted from moving picture encoding apparatus  100  to moving picture decoding apparatus  200 , then encoded data reconstructor  202  operates according to a flowchart shown in  FIG. 5 .  
      In the operation of encoded data reconstructor  202  shown in  FIG. 5 , N is “3”, moving picture encoding apparatus  100  has first moving picture encoder/sender  101 - 1  through third moving picture encoder/sender  101 - 3 , moving picture decoding apparatus  200  has first encoded data receiver  201 - 1  through third encoded data receiver  201 - 3 , and the compression ratio for frame encoding is successively higher in the order from first moving picture encoder/sender  101 - 1  through third moving picture encoder/sender  101 - 3 .  
      In  FIG. 5 , the steps represented by the same step numbers as those in  FIG. 4  represent the same processing as in  FIG. 4 , and steps S 501 , S 502  are added. Specifically, if a data error and a packet loss are present in the encoded data in the second packet reception buffer, then it is determined in step S 501  whether there are a data error and a packet loss in the encoded data in the third packet reception buffer. If there are not a data error and a packet loss, then the encoded data in the third packet reception buffer are transferred as encoded data to be decoded to variable-length decoder  251 .  
      If the encoded data of the nth frame cannot be received free of bit errors and packet losses by either one of the packet reception buffers, then the concealment process in step S 406  is performed.  
      As described above, by determining whether there are not a bit error and a packet loss in the encoded data of the frame received by the packet reception buffers in the ascending order of compression ratios for frame encoding, the encoded data are transferred as encoded data to be decoded to variable-length decoder  251  so that priority is given to the encoded data of the lower compression ratio.  
      If the compression ratios for frame encoding of second moving picture encoder/sender  101 - 2  and third moving picture encoder/sender  101 - 3  are the same as each other, then priority may be given to either one of their encoded data.  
      Alternatively, the encoded sent from first through Nth N moving picture encoder/senders  101 - 1  through  101 -N of moving picture encoding apparatus  100  may be ordered so that priority is given to the encoded data of the lower compression ratio, for example, and encoded data reconstructor  202  of moving picture decoding apparatus  200  may select encoded data of the highest order for each frame from a plurality of properly received encoded data.  
      In the present embodiment, first packet error detector/packet loss detector  213 - 1  may employ any process for detecting bit errors and packet losses in the first encoded packet data. For example, it may detect bit errors and packet losses based on the error detecting code and the frame/packet numbers that have been added by moving picture encoding apparatus  100 . Alternatively, if the encoded data transmission path has an error detecting function, then the detected result thereof may be employed. If information which identifies encoded frames is included in the encoded data, then the information included in the encoded data may be employed.  
      Likewise, second packet error detector/packet loss detector  213 - 2  may employ any process for detecting bit errors and packet losses in the first encoded packet data.  
      In the encoded data reconstructing sequence of encoded data reconstructor  202 , any processes of waiting for the reception of the encoded data of the nth frame may be employed in step S 401  insofar as they are capable of detecting packet losses while holding a packet transmission delay within a predetermined range.  
      In a further preferred specific example of the present embodiment, moving picture decoding apparatus  200  is connected to an Internet communication network, receives packet data sent from moving picture encoding apparatus  100  connected at another spot to the Internet communication network using the UDP/IP protocol, decodes moving picture encoded data included in the received UDP datagram, and displays an obtained moving picture on a display. The moving picture encoded data are data according to the MPEG-4 Visual process, for example. First packet error detector/packet loss detector  213 - 1  and second packet error detector/packet loss detector  213 - 2  detect a transmission error by calculating a check sum included in the UDP datagram. Moving picture data decoder  203  which comprises variable-length decoder  251 , residual decoder  252 , interframe prediction image generator  253 , decoded image calculator  254 , reference frame storage memory  255 , and frame scanner  256  is an ordinary decoding apparatus compatible with the MPEG-4 Visual process.  
      Variable-length decoder  251  variable-length-decodes data that are encoded according to the MPEG-4 Visual process to extract compression information such as DCT quantization coefficients, motion vectors, etc. Residual decoder  252  performs inverse quantization and two-dimensional inverse discrete cosine transform. Interframe prediction image generator  253  generates a motion-compensated image according to decoded motion vectors.  
     2ND EMBODIMENT  
      In the first embodiment described above, the first and second encoded packet data may be transmitted from moving picture encoding apparatus  100  to moving picture decoding apparatus  200  according to any processes. For making the present invention more effective to reduce significant corruptions of decoded images, it is preferable to employ a process for reducing the correlation between bit errors and packet losses that occur in the first encoded packet data and bit errors and packet losses that occur in the second encoded packet data which are produced by encoding the same frame image as with the first encoded packet data.  
       FIG. 6  shows a second embodiment for realizing such a preferable encoded packet data transmission process.  
      The second embodiment shown in  FIG. 6  has delay adder  601  for adding a constant or adaptively variable delay time to the second encoded packet data output from moving picture encoding apparatus  100  according to the first embodiment shown in  FIG. 2  and sending the data with the added delay time, multiplexer  602  for multiplexing the first encoded packet data output from moving picture encoding apparatus  100  and the second encoded packet data output from delay adder  601  and sending the multiplexed data to a transmission path, transmission path  603  for transmitting the data multiplexed by multiplexer  602  from the sending apparatus to the receiving apparatus, and demultiplexer  604  for receiving the data from transmission path  603 , demultiplexing the data into the first encoded packet data and the second encoded packet data, outputting them to moving picture decoding apparatus  200  according to the first embodiment.  
      The delay time that is added to the second encoded packet data by delay adder  601  is determined by a maximum burst time of bit errors and packet looses that occur in transmission path  603 . Therefore, even when a burst error occurs in transmission path  603 , since the probability that both the first and second encoded data produced by encoding the same frame are affected by the error is reduced, it is possible to reduce significant image quality deteriorations due to a loss of encoded frame data.  
      According to the second embodiment described above, moving picture encoding apparatus  100  encodes one moving picture data into two encoded data and sends the encoded data at a constant or adaptively variable time interval. Second encoder/sender  101 - 2  encodes frames encoded by first encoder/sender  101 - 1  using interframe prediction parameters and residual image data which are obtained by the encoding of the frames which is performed by first encoder/sender  101 - 1 . Moving picture decoding apparatus  200  on the reception side selects and decodes frames of encoded data which are of a low compression ratio and high image quality from the properly received encoded data. As a result, even if the transmission path is of low reliability, frequently causing transmission errors and packet errors of highly burst nature, the probability that both the two encoded data are transmitted in error is reduced, making it possible to prevent transmitted decoded images from suffering significant corruptions.  
      An increase caused in the transmission band when the second encoded data are sent may be reduced by increasing the compression ratio of the second encoded data.  
      Furthermore, since moving picture decoding apparatus  200  may decode only one of the two encoded data that are received, the amount of calculations that are required thereby is not appreciably greater than the amount of calculations that are required by ordinary moving picture decoding apparatus.  
      In the second embodiment, in addition to the advantages of the first embodiment, moving picture encoding apparatus  100  encodes one moving picture data into two encoded data and sends the encoded data at a constant or adaptively variable time interval. Therefore, even when a burst error occurs in the transmission path, since the probability that both the first and second encoded data produced by encoding the same frame are affected by the error is reduced, it is possible to reduce significant image quality deteriorations due to a loss of encoded frame data.  
     3RD EMBODIMENT  
      A third embodiment of the present invention will be described below.  
      The arrangement and operation of the third embodiment are substantially the same as those of the first embodiment, and comprises, as shown in  FIG. 1 , moving picture encoding apparatus  100 , moving picture decoding apparatus  200 , and transmission path  300  for transmitting encoded data. N represents the number of encoded data sent from moving picture encoding apparatus  100 .  
      The arrangement of moving picture encoding apparatus  100  is substantially the same as that of the first embodiment. However, operation of components of moving picture encoding apparatus  100  is different from that of the first embodiment.  
      Encoded data of an input frame image that is encoded by first moving picture encoder/sender  101 - 1  comprise one or plural packet data, each representing encoded interframe prediction parameters and residual image compression data with respect to an image area contained in the input frame image.  
      Second through Nth N moving picture encoder/senders  101 - 2  through  101 -N encode the image area included in all or part of the packets encoded by the first moving picture encoder/sender at a compression ratio higher than first moving picture encoder/sender  101 - 1 , using interframe prediction parameters and residual image data which are obtained the interframe prediction performed on the image area by first moving picture encoder/sender  101 - 1 , and sends the obtained encoded packet data to moving picture decoding apparatus  200 . Other operation details than described above are basically the same as those of the first embodiment.  
      The arrangement of moving picture decoding apparatus  200  is also substantially the same as that of the first embodiment. However, operation of components of moving picture decoding apparatus  200  is different from that of the first embodiment.  
      As with the first embodiment, encoded data reconstructor  202  selects one packet having the lowest compression ratio as encoded data to be decoded, from a maximum of N encoded packet data free of transmission errors and dropouts received by first through Nth encoded data receivers  201 - 1  through  201 -N. Encoded data reconstructor  202  selects packet data sent by moving picture encoding apparatus  100 . Other operation details than described above are basically the same as those of the first embodiment.  
      The arrangement and operation of the moving picture encoder/senders according to the third embodiment are substantially the same as the moving picture encoder/senders of the first embodiment shown in  FIG. 2 . The moving picture encoder/senders according to the third embodiment differ from moving picture encoder/senders of the first embodiment only as to operation of first encoded packet generator  115 - 1 , second encoded packet generator  115 - 2 , first packet error detecting code-frame/packet identification number adder  116 - 1 , and second packet error detecting code-frame/packet identification number adder  116 - 2 .  
      In moving picture encoding apparatus  100  according to the present embodiment, first encoded packet generator  115 - 1  and second encoded packet generator  115 - 2  generate encoded packet data such that an image area contained in the encoded packet data generated by first encoded packet generator  115 - 1  and an image area contained in the encoded packet data generated by second encoded packet generator  115 - 2  coincide with each other.  
      First packet error detecting code-frame/packet identification number adder  116 - 1 , and second packet error detecting code-frame/packet identification number adder  116 - 2  operate to add the same packet identification number to encoded packet data corresponding to the same image area of the same frame. However, if the packet data encoded by first and second encoded packet generators  115 - 1 ,  115 - 2  contain a frame number and information for identifying the position of the image area contained in the packet data, then no frame/packet identification number may be added.  
      Other operation details of the processors than described above are the same as those of the first embodiment.  
      In a preferred specific example of the present embodiment, the MPEG Visual process is used for the compression encoding of moving pictures. According to this process, an input image frame is divided into rectangular areas of constant size called macroblocks and then compressed, and the compressed image information in each of the macroblocks is encoded in packets called video packets into a bit string. The video packets contain compressed data with respect to any desired number of macroblocks, and the bit string data encoded by this process can be decoded in video packets.  
      First encoded packet generator  115 - 1  and second encoded packet generator  115 - 2  output encoded data in video packets. Video packets encoded by second encoded packet generator  115 - 2  are generated so as to contain macroblocks in the same area as the video packets encoded by first encoded packet generator  115 - 1 .  
      The arrangement and operation of moving picture decoding apparatus  200  according to the present embodiment are substantially the same as those of the moving picture decoding apparatus according to the first embodiment, except that only operation of encoded data reconstructor  202  in  FIG. 3  is different.  
      An encoded data reconstructing sequence of encoded data reconstructor  202  according to the third embodiment will be described below with reference to a flowchart shown in  FIG. 7 . The sequence shown in  FIG. 7  represents a process of reconstructing encoded data of an nth frame where n is an integer.  
      In step S 701 , control waits until a time which is the sum of a time when all encoded data of the nth frame are to arrive at first packet reception buffer  211 - 1  and second packet reception buffer  211 - 2  and a predetermined allowable maximum delay time. Then, control goes to step S 702 .  
      In step S 702 , a minimum value of the packet number of the nth frame is stored in a variable a which stores the packet number, and a maximum value of the packet number of the nth frame is stored in a variable b.  
      In step S 703 , the value of the variable a is substituted for a variable i which stores the packet number. Then, control starts a repetitive loop from step S 704 .  
      In step S 704 , the following branching process is performed depending on the results of errors and packet losses detected by first packet error detector/packet loss detector  213 - 1 : If an ith packet of the nth frame is received by first packet reception buffer  211 - 1  and no error is detected in the data, then control goes to step S 705 . Otherwise, control goes to step S 706 .  
      In step S 705 , the ith packet data of the nth frame output from first encoded data extractor  212 - 1  is transferred as encoded data to be decoded to variable-length decoder  251 . Then, control goes to step S 709 .  
      In step S 706 , the following branching process is performed depending on the results of errors and packet losses detected by second packet error detector/packet loss detector  213 - 2 : If the ith packet of the nth frame is received by second packet reception buffer  211 - 2  and no error is detected in the data, then control goes to step S 707 . Otherwise, control goes to step S 708 .  
      In step S 707 , the ith packet data of the nth frame output from second encoded data extractor  212 - 2  is transferred as encoded data to be decoded to variable-length decoder  251 . Then, control goes to step S 709 .  
      Control proceeds to step S 708  when the ith packet data of the nth frame cannot be received free of bit errors and packet losses by either one of the first and second packet reception buffers. In step S 708 , therefore, a concealment process for making less visible corruptions of a decoded image area contained in the ith packet data is carried out by an appropriate method.  
      For example, a command is sent to the moving picture data decoder to use a decoded image of a preceding (n-1)th frame as a decoded image contained in the ith packet data of the nth frame. Alternatively, if first packet reception buffer  211 - 1  has received incomplete ith packet data of the nth frame, then the received packet data is used for decoding the nth frame. If the packet data is not received by first packet reception buffer  211 - 1  and second packet reception buffer  211 - 2  has received incomplete ith packet data of the nth frame, then the packet data obtained by the second packet reception buffer is used for decoding the nth frame. If the ith packet data of the nth frame is not received by both the first and second packet reception buffers, then a decoded image of a preceding (n-1)th frame is displayed.  
      After the above concealment process is performed in step S 708 , control goes to step S 709 .  
      In step S 709 , the variable i is incremented by 1. In step S 710 , it is determined whether the variable i does not exceed the value of the variable b. If the variable i does not exceed the value of the variable b, then the processing from step S 704  is repeated. If the variable i exceeds the value of the variable b, then the repetitive process is finished, and the process of reconstructing encoded data of the nth frame is put to an end.  
      The operation of encoded data reconstructor  202  according to the third embodiment has been described above.  
       FIG. 7  illustrates the operation of encoded data reconstructor  202  where, as shown in  FIGS. 2 and 3 , N shown in  FIG. 1  is “2”, moving picture encoding apparatus  100  has first moving picture encoder/sender  101 - 1  and second moving picture encoder/sender  101 - 2 , and moving picture decoding apparatus  200  has first encoded data receiver  201 - 1  and second encoded data receiver  201 - 2 .  
      If N shown in  FIG. 1  is “3” and three or more encoded data are transmitted from moving picture encoding apparatus  100  to moving picture decoding apparatus  200 , then encoded data reconstructor  202  operates according to a flowchart shown in  FIG. 8 .  
      In the operation of encoded data reconstructor  202  shown in  FIG. 8 , N is “3”, moving picture encoding apparatus  100  has first moving picture encoder/sender  101 - 1  through third moving picture encoder/sender  101 - 3 , moving picture decoding apparatus  200  has first encoded data receiver  201 - 1  through third encoded data receiver  201 - 3 , and the compression ratio for frame encoding is successively higher in the order from first moving picture encoder/sender  101 - 1  through third moving picture encoder/sender  101 - 3 .  
      In  FIG. 8 , the steps represented by the same step numbers as those in  FIG. 7  represent the same processing as in  FIG. 7 , and steps S 801 , S 802  are added. Specifically, if the ith packet is not present in the second packet reception buffer or if the ith packet is present in the second packet reception buffer, but suffers a bit error, then if the ith packet of the nth frame is received in the third packet reception buffer and no error is detected in the received data in step S 801 , the ith packet data of the nth frame output from third encoded data extractor  212 - 3  is transferred as encoded data to be decoded to variable-length decoder  251  in step S 802 .  
      If the ith packet of the nth frame is present in any one of the packet reception buffers or if the ith packet of the nth frame is present in either one of the packet reception buffers, but a bit error is detected in the data, then the concealment process in step S 708  is performed.  
      As described above, the packet data having the low compression ratio for frame encoding is preferentially transferred as encoded data to variable-length decoder  251 .  
      If the compression ratios for frame encoding of second moving picture encoder/sender  101 - 2  and third moving picture encoder/sender  101 - 3  are the same as each other, then priority may be given to either one of their encoded data.  
      In the encoded data reconstructing sequence of encoded data reconstructor  202 , any processes of waiting for the reception of the encoded data of the nth frame may be employed in step S 701  insofar as they are capable of detecting packet losses while holding a packet transmission delay within a predetermined range.  
      According to the third embodiment as described above, moving picture encoding apparatus  100  encodes one moving picture data into two encoded data and sends the encoded data at a constant or adaptively variable time interval. Second moving picture encoder/sender  101 - 2  encodes the image area included in the packets encoded by first moving picture encoder/sender  101 - 1 , using interframe prediction parameters and residual image data which are obtained the interframe prediction performed by first moving picture encoder/sender  101 - 1 . The reception side selects and decodes packets of encoded data which are of a low compression ratio and high image quality from the properly received encoded data.  
      As a result, even if the transmission path is of low reliability, frequently causing transmission errors and packet errors of highly burst nature, the probability that both the two encoded data are transmitted in error is reduced, making it possible to prevent transmitted decoded images from suffering significant corruptions. An increase caused in the transmission band when the second encoded data are sent may be reduced by increasing the compression ratio of the second encoded data. Furthermore, since moving picture decoding apparatus  200  may decode only one of the two encoded data that are received, the amount of calculations that are required thereby is not appreciably greater than the amount of calculations that are required by ordinary moving picture decoding apparatus.  
     4TH EMBODIMENT  
      A moving picture transmission system according to a fourth embodiment of the present invention will be described below.  
      The arrangement and operation of the present embodiment are substantially the same as those of the first embodiment, and comprises, as shown in  FIG. 1 , moving picture encoding apparatus  100 , moving picture decoding apparatus  200 , and transmission path  300  for transmitting encoded data.  
      In the present embodiment, operation of components of moving picture encoding apparatus  100  is different from that of the first embodiment.  
      Second through Nth N moving picture encoder/senders  101 - 2  through  101 -N encode an input frame image using a reference frame image that is used in the interframe prediction performed on the frame by first moving picture encoder/sender  101 - 1 .  
      Second through Nth N moving picture encoder/senders  101 - 2  through  101 -N may encode interframe prediction parameters and residual image data different from those in first moving picture encoder/sender  101 - 1 , which are obtained by interframe prediction under a different control process from first moving picture encoder/sender  101 - 1 . Other operation details than described above are basically the same as those of the first embodiment.  
      The arrangement of moving picture decoding apparatus  200  is exactly the same as that of the first embodiment.  
       FIG. 9  shows a detailed arrangement of moving picture encoding apparatus  10  according to the fourth embodiment of the present invention. In  FIG. 9 , the number N of encoded data output by the apparatus is illustrated as “2” for the sake of brevity.  
      First moving picture encoder/sender  101 - 1  of moving picture encoding apparatus  10  according to the fourth embodiment shown in  FIG. 9  is identical in arrangement and operation to that of the first embodiment shown in  FIG. 2 .  
      Second moving picture encoder/sender  101 - 2  according to the present embodiment is different in arrangement and operation from that of the first embodiment shown in  FIG. 2 . Second moving picture encoder/sender  101 - 2  comprises second interframe predictor  112 - 2 , second residual calculator  113 - 2 , second residual compression encoder  114 - 2 , second encoded packet generator  115 - 2 , and second packet error detecting code-frame/packet identification number adder  116 - 2 .  
      Second interframe predictor  112 - 2  performs interframe prediction on an image input from frame scanner  111  based on one or more decoded images stored in reference frame storage memory  119 . Second residual calculator  113 - 2  subtracts a prediction image obtained by second interframe predictor  112 - 2  from the input frame image to calculate a residual. Second residual compression encoder  114 - 2  encodes the residual image obtained by second residual calculator  113 - 2  at a compression ratio higher than that of first residual compression encoder  114 - 1 .  
      Second encoded packet generator  115 - 2  variable-length-encodes the interframe predictive parameters obtained by second interframe predictor  112 - 2  and the compressed data of the residual obtained by second residual compression encoder  114 - 2  into a bit string and outputs the bit string in packets. Second packet error detecting code-frame/packet identification number adder  116 - 2  adds an error detecting code and frame/packet identification numbers in order for the receiving apparatus to detect transmission errors and packet losses of the compressed packet data output by second encoded packet generator  115 - 2 . The above processors operate to obtain second moving picture encoded data, which are sent in packets by a predetermining sending means.  
      Second interframe predictor  112 - 2  performs interframe prediction using the same input frame image and reference frame image as those used by first interframe predictor  112 - 1 . No problem arises if second interframe predictor  112 - 2  produces interframe prediction parameters and prediction images that are different from those produced by first interframe predictor  112 - 1 . Therefore, the advantages of the present invention can be increased by second interframe predictor  112 - 2  which determines prediction parameters by attaching more importance to the encoded length of interframe prediction parameters than first interframe predictor  112 - 1 .  
      According to the fourth embodiment, as described above, moving picture encoding apparatus  100  encodes one moving picture data into two encoded data and sends the encoded data at a constant or adaptively variable time interval. Second moving picture encoder/sender  101 - 2  encodes frames encoded by first moving picture encoder/sender  101 - 1  using a reference frame image used in the encoding of the frames which is performed by first moving encoder/sender  101 - 1 . The reception side selects and decodes frames of encoded data which are of a low compression ratio and high image quality from the properly received encoded data.  
      As a result, even if the transmission path is of low reliability, frequently causing transmission errors and packet errors of highly burst nature, the probability that both the two encoded data are transmitted in error is reduced, making it possible to prevent transmitted decoded images from suffering significant corruptions.  
      An increase caused in the transmission band when the second encoded data are sent may be reduced by increasing the compression ratio of the second encoded data. Furthermore, since moving picture decoding apparatus  200  may decode only one of the two encoded data that are received, the amount of calculations that are required thereby is not appreciably greater than the amount of calculations that are required by ordinary moving picture decoding apparatus.  
     5TH EMBODIMENT  
      A moving picture transmission system according to a fifth embodiment of the present invention will be described below.  
      The overall arrangement of the present embodiment is the same as those of the fourth embodiment, and comprises, as shown in  FIG. 1 , moving picture encoding apparatus  100 , moving picture decoding apparatus  200 , and transmission path  300  for transmitting encoded data.  
      The arrangement of moving picture encoding apparatus  100  is the same as the fourth embodiment, but operation of components of moving picture encoding apparatus  100  is different from that of the fourth embodiment.  
      Encoded data of an input frame image that is encoded by first moving picture encoder/sender  101 - 1  comprise one or plural packet data, each representing encoded interframe prediction parameters and residual image compression data with respect to an image area contained in the input frame image.  
      Second through Nth N moving picture encoder/senders  101 - 2  through  101 -N encode the image area included in all or part of the packets encoded by first moving picture encoder/sender  101 - 1  at a compression ratio higher than first moving picture encoder/sender  101 - 1 , using a reference frame image used in the interframe prediction performed on the image area by first moving picture encoder/sender  101 - 1 , and sends the obtained encoded packet data to moving picture decoding apparatus  200 . Other operation details than described above are basically the same as those of the fourth embodiment.  
      The arrangement of moving picture decoding apparatus  200  is exactly the same as that of the third embodiment.  
      The arrangement and operation of moving picture encoding apparatus  100  according to the present embodiment are substantially the same as the moving picture encoding apparatus of the fourth embodiment shown in  FIG. 9 . Moving picture encoding apparatus  100  according to the present embodiment differs therefrom only as to operation of first encoded packet generator  115 - 1 , second encoded packet generator  115 - 2 , first packet error detecting code-frame/packet identification number adder  116 - 1 , and second packet error detecting code-frame/packet identification number adder  116 - 2 . In moving picture encoding apparatus  100  according to the present embodiment, first encoded packet generator  115 - 1  and second encoded packet generator  115 - 2  generate encoded packet data such that an image area contained in the encoded packet data generated by first encoded packet generator  115 - 1  and an image area contained in the encoded packet data generated by second encoded packet generator  115 - 2  coincide with each other.  
      First packet error detecting code-frame/packet identification number adder  116 - 1 , and second packet error detecting code-frame/packet identification number adder  116 - 2  operate to add the same packet identification number to encoded packet data corresponding to the same image area of the same frame. However, if the packet data encoded by first and second encoded packet generators  115 - 1 ,  115 - 2  contain a frame number and information for identifying the position of the image area contained in the packet data, then no frame/packet identification number may be added.  
      Other operation details of the processors than described above are the same as those of the third embodiment.  
      According to the fourth embodiment as described above, first moving picture encoder/sender  101 - 1  of moving picture encoding apparatus  100  encodes one moving picture data into two encoded data and sends the encoded data at a constant or adaptively variable time interval.  
      Second moving picture encoder/sender  101 - 2  encodes the image area included in the packets encoded by first moving picture encoder/sender  101 - 1 , using a reference frame image used in the encoding of the frames which is performed by first moving picture encoder/sender  101 - 1 . The reception side selects and decodes packets of encoded data which are of a low compression ratio and high image quality from the properly received encoded data.  
      As a result, even if the transmission path is of low reliability, frequently causing transmission errors and packet errors of highly burst nature, the probability that both the two encoded data are transmitted in error is reduced, making it possible to prevent transmitted decoded images from suffering significant degradation.  
      An increase caused in the transmission band when the second encoded data are sent may be reduced by increasing the compression ratio of the second encoded data.  
      Furthermore, since moving picture decoding apparatus  200  may decode only one of the two encoded data that are received, the amount of calculations that are required thereby is not appreciably greater than the amount of calculations that are required by ordinary moving picture decoding apparatus.  
      The moving picture transmission system according to each of the above embodiments may be realized by hardware-implemented functions of the moving picture encoding apparatus and the moving picture decoding apparatus, or by loading a moving picture transmission program comprising moving picture encoding program  800  and moving picture decoding program  900  which have the above functions of the moving picture encoding apparatus and the moving picture decoding apparatus into a memory of a computer processor and executing the loaded moving picture transmission program. Moving picture encoding program  800  and moving picture decoding program  900  are stored in a magnetic disk, a semiconductor memory, or any of other recording mediums, are loaded from the recording medium into the computer processor, and control operation of the computer processor to achieve the above functions.  
      While the present invention has been described with respect to the preferred embodiments, the present invention is not limited to the above embodiments, but various modifications may be made within the scope of the technical concept of the invention.