Abstract:
A content receiver terminal device for receiving video content which belongs to one of plural channels and is distributed at two different bit rates includes a selector for selecting one of the channels, and a memory for receiving video content belonging to the channel selected and stores the video content received. The content receiver terminal device also includes a reproducer which, in case the channel selector has selected a new channel, first reads out and reproduces content of a lower bit rate of the video content from the memory, and subsequently reproduces content of a higher bit rate. Thus, when viewing multi-channel video content transmitted over a telecommunications network suffering from fluctuation in communication speed, the zapping response is improved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a content receiver terminal device configured for receiving multi-channel video content distributed over a telecommunications network. 
         [0003]    2. Description of the Background Art 
         [0004]    In distributing video content over a telecommunications network, it may occur that the network undergoes fluctuation in its communication or transmission speed. In order to solve such a fluctuation difficulty, the content receiver terminal device serving as a client is provided with a receiver buffer such as to compensate for the fluctuation. After a predetermined amount of data, for example, corresponding to ten seconds, has been stored in the buffer, the data is developed from the buffer to be reproduced. This prevents the reproduction of the data from being interrupted as would otherwise be ascribable to fluctuation in communication speed. 
         [0005]    In that case, however, data is reproduced necessarily with delay, of which the time corresponds to an amount of data stored in the receiver buffer, e.g. ten seconds, in the content receiver terminal device. 
         [0006]    In order to remove the delay problem, the streaming player system disclosed by Japanese patent laid-open publication No. 2006-80612 is adapted to download beforehand the beginning portions of streaming data of plural video contents into the content receiver terminal device. When one video content is selected or switched for viewing, the streaming player system starts receiving the content from a network and at the same time plays the beginning portion of the streaming data of that content downloaded in advance. 
         [0007]    When the downloaded beginning portion of the content has completely been played, the predetermined amount of data might have been stored in the receiver buffer. The receiver buffer may be read from the portion continuing the beginning portion to thereby play the content in succession from the end of the beginning portion. The streaming player system of the Japanese &#39;612 publication is thus structured to store and hold the beginning portions of contents beforehand so as to establish the viewing of content free of reproduction delay. 
         [0008]    The technique of the Japanese &#39;612 publication is effective for video content already recorded, indeed. It is however not so advantageously applicable to video content transmitted on a real-time basis, such as TV (television) broadcast. With real-time video content, it is difficult to prepare beforehand partial streaming data of video content. 
         [0009]    When selecting or changing over video content in a content receiver terminal device, the content selected cannot be played until the receiver buffer is cleared and stores a predetermined amount of data of that content, with the result that the content receiver terminal device is deteriorated in response characteristics. In the context, the operation of selecting or changing over video content will be referred to below as zapping. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a content receiver terminal device which is improved in response characteristics of zapping in viewing multi-channel video content over a telecommunications network undergoing fluctuations in communication or transmission speed. 
         [0011]    In accordance with the present invention, a content receiver terminal device for receiving video content belonging to one of a plurality of channels and distributed at two different bit rates comprises a channel selector for selecting one of the channels, a buffer for receiving video content belonging to the channel selected and for storing the video content received, and a reproducer for first performing, in case the channel selector has selected a new channel, a preliminary reproducing operation of reading out and reproducing content of a lower bit rate of the video content from the buffer, and for subsequently performing an actual reproducing operation of content of a higher bit rate. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The objects and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0013]      FIG. 1  is a schematic block diagram showing a preferred embodiment of a content distribution server and a content receiver terminal device according to the present invention; 
           [0014]      FIG. 2  is a time chart useful for understanding the operation of various parts of the content distribution server and the content receiver terminal device in accordance with the preferred embodiment; 
           [0015]      FIG. 3  is a flow chart useful for understanding the operation of the content receiver terminal device in accordance with the preferred embodiment; and 
           [0016]      FIG. 4  diagrammatically shows channel transition patterns as used in accordance with the preferred embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]      FIG. 1  is a schematic block diagram showing a preferred embodiment of a content distribution system in accordance with the present invention. The illustrative system is composed of a plurality (n) of channel distribution servers  1 -N, where  n  is a natural number and N is an integer of from 1 to  n , inclusive. The illustrative system further includes a telecommunications network  7 , and a content receiver terminal device  36  functioning as a client, all those components being interconnected as illustrated. The channel distribution servers  1 -N distribute video contents on the respective video channels to the network  7 . Specifically, the channel distribution servers  1 - 1 ,  1 - 2  to  1 -N are provided for channels # 1 , # 2  to #n, respectively. 
         [0018]    Each of the channel distribution servers  1 -N comprises an audio and video (AV) signal input unit  2  and a simulcast encoder  4 . The AV signal input unit  2  receives, e.g. TV broadcast signals carried on electromagnetic waves to output an AV signal  3  including a video and an audio signal. In the patent application, signals are designated with reference numerals of connections on which they are conveyed. 
         [0019]    The simulcast encoder  4  receives the AV signal  3  and encodes the received signal  3  at two bit rates different from each other, i.e. higher and lower bit rates, to output resulting data over the network  7 . The data with the higher bit rate is termed a content stream  5 -N and the data with the lower bit rate is termed a reference stream  6 -N. 
         [0020]    The content stream  5 -N and the reference stream  6 -N, distributed from each of the channel distribution servers  1 -N, are transmitted over the network  7  and a transmission line  8  to the content receiver terminal device  36 . 
         [0021]    The content receiver terminal device  36  is composed of a receiver  9 , three buffers, i.e. first buffer  15 , second buffer  16  and third buffer  17 , three decoders, i.e. first decoder  24 , second decoder  25  and third decoder  26 , a driver  31 , a TV monitor  33 , a loudspeaker  35  and a system controller  19 , which are interconnected as illustrated. 
         [0022]    The receiver  9  receives transmitted data  8  and in turn produces, under the control of the system controller  19 , three streams of data, i.e. first stream  10 , second stream  11  and third stream  12 , to the three buffers  15 ,  16  and  17 , respectively. 
         [0023]    Under the control of the controller  19 , the buffers  15 ,  16  and  17  clear data already stored therein and newly store therein the data streams  10 ,  11  and  12  sent from the receiver  9 , respectively. 
         [0024]    The buffers  15 ,  16  and  17  are responsive to requests provided from the decoders  24 ,  25  and  26 , respectively, to output the data stored in the respective buffers  15 ,  16  and  17  in the form of first buffer signal  20 , second buffer signal  21  and third buffer signal  22 , respectively, in a FIFO (First-In First-Out) fashion. 
         [0025]    The buffers  15 ,  16  and  17  also output a buffer status signal  18  to the controller  19 . The buffer status signal  18  indicates whether or not the volume or amount of data stored in the buffer is equal to or greater than a predetermined value. The amount of data stored in the buffer is referred to below as residual buffer data amount  37 ,  FIG. 2 . 
         [0026]    The decoders  24 ,  25  and  26  receive the buffer signals  20 ,  21  and  22  from the buffers  15 ,  16  and  17 , respectively. The decoders  24 ,  25  and  26  decode the respective signals received to generate and output three terminal AV signals, i.e. first terminal AV signal  27 , second terminal AV signal  28  and third terminal AV signal  29 , each of which includes video and audio signals. 
         [0027]    The decoders  24 ,  25  and  26  receive from the controller  19  a decoder control signal  23  indicating whether to output terminal AV signals  27 ,  28  and  29 , respectively, which will be described later. The decoders  24 ,  25  and  26  output terminal AV signals  27 ,  28  and  29  in case the decoder control signal  23  indicates that the terminal AV signals  27 ,  28  and  29  be output, respectively. 
         [0028]    The driver  31  receives the terminal AV signals  27 ,  28  and  29 , and produces therefrom a video signal  32  and an audio signal  34 . The TV monitor  33  receives the video signal  32  from the driver  31  to reproduce or play and display video content represented by the video signal  32  in the form of visual image. The loudspeaker  35  receives the audio signal  34  from the driver  31  to reproduce the audio signal  34  received in the form of audible sound. 
         [0029]    The controller  19  is responsive to a signal  30  corresponding to operation for zapping manually entered on an operation panel, not shown, and also to the buffer status signal  18  to supply a channel control signal  14  to the receiver  9  as well as to supply the buffer control signal  13  to the buffers  15 ,  16  and  17  and the decoder control signal  23  to one of the decoders, i.e. first decoder  24  in this example. 
         [0030]    In the present embodiment, the content stream  5 -N and the reference stream  6 -N are output from each of the  n  channel distribution servers  1 -N. The content receiver terminal device  36  is provided with a remote controller, not shown, which is adapted to be responsive to manipulation of the user so as to enable him or her to instruct a viewing and/or listening start, represented by a signal  41 , or designate the channel number desired to be viewed or watched, represented by the zapping operation signal  30 . 
         [0031]    Now, reference will be made to  FIG. 2 , which is useful for understanding the operation of the content receiver terminal device  36  of the present illustrative embodiment. In operation, the content receiver terminal device  36  receives instructions for the viewing start  41  given by, e.g. the remote controller. The controller  19  then discriminates the bit rate of the received signal  8  and then imparts to the receiver  9  the channel control signal  14  indicative of a default value. It is assumed that the default value specifies the first stream afforded to the content stream  5 - 2  on the channel # 2 , the second stream afforded to the reference stream  6 - 1  on the channel # 1  as a preliminary channel, and the third stream afforded to the reference stream  6 - 3  on the channel # 3  as another preliminary channel. 
         [0032]    The controller  19  transmits the buffer control signal  13  to the three buffers  15 ,  16  and  17  to clear their contents. This clears the contents of the three buffers  15 ,  16  and  17 , which in turn change the respective buffer status signals  18  to NOT_READY, meaning that the respective residual buffer data amount  37  is only small, and output the signals  18  to the system controller  23 . 
         [0033]    The receiver  9  receives the three channel streams as set from the controller  19 , and in turn the streams of data will gradually be stored in the respectively three buffers  15 ,  16  and  17 . The controller  19  then detects the residual buffer data amount  37  from the buffer status signals  18 . If the controller  19  finds the residual data amount  37  to be small, then it turns the decoder control signal  23  off, i.e. to its disable state. The three decoders  24 ,  25  and  26  thereby do not start decoding  38 ,  FIG. 2 , thus no output being developed on the display screen of the TV monitor  33  and on the loudspeaker  35 . 
         [0034]    If the buffers  15 ,  16  and  17  determine that the respective residual buffer data amounts  37  have reached the predetermined value, then they turn the buffer status signal  18  to READY, meaning that the residual buffer data amounts  37  are not less than the predetermined value. 
         [0035]    The system controller  19  instructs the decoders  24 ,  25  and  26  to start decoding  38  by the decoder control signal  23 . The controller  19  turns the first decoder  24  on by the decoder control signal  23  instructing the first stream  10  received as a content stream  5 - 2  on the channel # 2  to be visualized on the display screen of the TV monitor  33  and output to the loudspeaker  35 , thus enabling the first decoder  24  to output the first AV signal  27  as a decoder output signal  39 ,  FIG. 2 . 
         [0036]    On the other hand, to the second decoder  25  and the third decoder  26 , the system controller  19  provides the decoder control signal  23  instructing both of them to be turned off, i.e. disabled. Thus, both decoders  25  and  26  performs decoding internally so as to output neither the second terminal AV signal  28  nor the third terminal AV signal  29  to the driver  31 . Thence, the video signal  32  and the audio signal  34 , corresponding to the content stream  5 - 2  on the channel # 2 , will be output on the display screen of the TV monitor  33  and on the loudspeaker  35 , respectively, as depicted as a reproduction of received data  40  in  FIG. 2 . 
         [0037]    Now, the operation of selecting the channel # 3  will be carried out by using, e.g. the remote controller. This process is represented as zapping  30 , which will now be described with reference to  FIG. 2  again. In response, the controller  19  determines the bit rate of the received signal  8  and detects that the reference stream  6 - 3  on the channel # 3  exists on the third stream  12 . 
         [0038]    The controller  19  then transmits the buffer control signal  13  to clear the contents of the first buffer  15  and the second buffer  16  corresponding to the other streams. The first buffer  15  and the second buffer  16  change the buffer status signals  18  to NOT_READY. 
         [0039]    The controller  19  then outputs the channel control signal  14  to allocate the content stream  5 - 3  on the channel # 3  to the first stream  10  and to allocate a reference stream  6 - 2  on the channel # 2  to the second stream  11 . The controller  19  begins to store the content stream  5 - 3  on the channel # 3  in the first buffer  15  and to store the stream data of the reference stream  6 - 2  on the channel # 2  in the second buffer  16 . 
         [0040]    The controller  19  also turns the first decoder  24  and the second decoder  25  off by the decoder control signal  23 . The controller  19  further instructs the third decoder  26  to be turned on, the third decoder  26  corresponding to the reference stream  6 - 3  on the channel # 3 . 
         [0041]    The residual buffer data amount of the first buffer  15  is detected, and, if the residual data amount is found to be not sufficient, the video signal  32  and the audio signal  34 , corresponding to the reference stream  6 - 3  on the channel # 3 , are output on the display screen of the TV monitor  33  and the loudspeaker  35 , as from the time point of the zapping operation  30 . 
         [0042]    The residual buffer data amounts of the first buffer  15  and the second buffer  16  once become zero. Subsequently, data of the content stream  5 - 3  on the channel # 3  and the reference stream  6 - 2  on the channel # 2  are gradually stored in the first and second buffers, respectively. 
         [0043]    When it is determined that the residual buffer data amount of the first buffer  15  has reached the predetermined value, the buffer status signal  18  for the first buffer  15  changes to READY. Upon detection that the first buffer  15  is READY, the controller  19  instructs the first decoder  24 , dealing with the content stream  5 - 3  on the channel # 3 , to be turned on by the decoder control signal  23 , and turns off the second decoder  25  and the third decoder  26 . 
         [0044]    This causes the video signal  32  and the video signal  34 , corresponding to the content stream  5 - 3  on the channel # 3 , to be output on the display screen of the TV monitor  33  and on the loudspeaker  35 , respectively. 
         [0045]    The controller  19  outputs the buffer control signal  13  to clear the third buffer  17 , while outputting the channel control signal  14  to the receiver  9  to cause the reference stream  6 - 4  on the channel # 4 , as the preliminary channel, to be stored in the third buffer  17 . 
         [0046]    In the foregoing, the operation of the content receiver terminal device  36  has been described separately for viewing start and for zapping. The receiving routine of the receiver terminal device  36  will now be briefly described with reference to  FIG. 3 . 
         [0047]    This receiving routine is carried out by the controller  19 , e.g. at a predetermined time interval. When the processing enters the receiving routine, it is checked whether or not a new channel has been designated (step S 1 ). If a new channel has been designated, bit streams of higher and lower bit rates of the designated channel are received (step S 2 ). 
         [0048]    The data received are then transmitted to the buffer (step S 3 ). It is checked whether or not the designated channel and the preliminary channel are coincident with each other (step S 4 ). When the designated channel and the preliminary channel are coincident with each other, the preliminary channel data start to be decoded and reproduced (step S 5 ). When the designated channel and the preliminary channel are not coincident with each other, the preliminary channel data are not decoded or reproduced. 
         [0049]    It is then checked whether or not the residual buffer data amount is sufficient (step S 6 ). In case the residual buffer data amount is found to be insufficient, received data of the lower bit rate are decoded and reproduced (step S 7 ). The received data are reproduced in the form of preliminary reproducing or playing operation on the screen of the TV monitor  33  and by the loudspeaker  35 . In the step S 6 , if the residual buffer data amount  37  is found to be sufficient, then the received data of the higher bit rate are decoded (step S 8 ) and reproduced in the form of actual reproducing or playing operation on the screen of the TV monitor  33  and by the loudspeaker  35  (step S 9 ). 
         [0050]    In the foregoing description, a default channel is designated at the time of viewing start and bit streams of both higher and lower bit rates are captured. However, capturing the bit stream of the lower bit rate may be dispensed with. 
         [0051]    The zapping operation  30  for the channel # 3  has been described in a case where the channels # 2  and # 4  are selected as reference streams and received simultaneously. The instant illustrative embodiment uses the statistic information of transition patterns of past viewing or watching channels to settle two channels of higher transition probability or channels neighboring to the channel presently under reception as preliminary channels and to simultaneously receive the content of the lower bit rate on the so settled preliminary channels as reference streams, thereby improving zapping response characteristics. In that manner, the content receiver terminal device  36  utilizes the channel selecting histories of the users and holds the transition patterns of the past viewing channels. 
         [0052]      FIG. 4  will be used for describing the channel control operation by the system controller  19 , and specifically shows, for the case of n=5, the probabilistic distribution of the combinations of channel numbers currently viewed as a content stream and a content stream to be viewed next. For instance, the probability of transition from the channel # 3  is the channels # 4 , # 2 , # 5  and # 1  in the falling order of the probability. If the content stream is thus the channel # 3 , then the channels # 4  and # 2  are selected as the reference streams, which are adapted to be received simultaneously. 
         [0053]    In the present embodiment, the content receiver terminal device  36  simultaneously receives and decodes reference streams on two channels distinct from the content stream currently being viewed. When changing over the content stream desired to be viewed, if the reference stream corresponding to the channel desired to be viewed has already been received, this reference stream will be reproduced or played, and at the same time the content stream on that channel will be received. Thereafter, when that content stream has become playable, the channel is changed over to the content stream, which will then be reproduced. 
         [0054]    In the above-described embodiment, reference streams on two channels are received simultaneously with a designated channel. Alternatively, the system may be adapted such that a reference stream on a single channel is received simultaneously with a designated channel. 
         [0055]    In the above-described embodiment also, so far as a reference stream is received, the decoders continue in decoding operation. Alternatively, the system may be structured such that the decoders operate only during the time when a decoding output is required by the subsequent driver  31 . 
         [0056]    The entire disclosure of Japanese patent application No. 2006-205093 filed on Jul. 27, 2006, including the specification, claims, accompanying drawings and abstract of the disclosure, is incorporated herein by reference in its entirety. 
         [0057]    While the present invention has been described with reference to the particular illustrative embodiment, it is not to be restricted by the embodiment. It is to be appreciated that those skilled in the art can change or modify the embodiment without departing from the scope and spirit of the present invention.