Patent Publication Number: US-10334293-B2

Title: Multiplexing apparatus, receiving apparatus, multiplexing method, and delay adjustment method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional Application of U.S. patent application Ser. No. 15/269,515, filed Sep. 19, 2016, which is a Continuation Application of PCT Application No. PCT/JP2015/054335, filed Feb. 17, 2015 and based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-060756, filed Mar. 24, 2014, the entire contents of both which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a multiplexing apparatus and a receiving apparatus used in a broadcasting system that transmits data using MMT (MPEG Multimedia Transport), and a multiplexing method and a delay adjustment method used by these apparatuses. 
     BACKGROUND 
     In current broadcasting systems, the MPEG-2 TS (Moving Picture Experts Group-2 Transport Stream) and RTP (Real-time Transport Stream) media transport schemes are widely used. There are various limits to these schemes when making broadcasting and communication cooperate. MMT (MPEG Multimedia Transport) that is a new media transport scheme assuming use of various networks using MPEG has been proposed. 
     In a broadcasting system that employs MMT, a receiving apparatus receives an MMT stream transmitted from transmission equipment. The transmission equipment includes, for example, a video sending apparatus, an encoding apparatus, a multiplexing apparatus, and a transmitting apparatus. The multiplexing apparatus multiplexes MMT packets output from the encoding apparatus. The transmitting apparatus transmits the multiplexed MMT packet as an MMT stream. When outputting an MMT packet to the transmitting apparatus, the multiplexing apparatus adds a time stamp representing an output time Tt to the MMT packet. Note that a time stamp representing a presentation time Tp of an MPU (Media Processing Unit) formed from the payload of the MMT packet is added to an SI (Service Information) packet included in the MMT packet. 
     The receiving apparatus receives the transmitted MMT stream. At this time, because of the influence of the transmission channel, the MMT stream received by the receiving apparatus has a delay Ad with respect to the output time Tt at which the multiplexing apparatus outputs the MMT packet. The receiving apparatus compares the time of reception of the MMT stream with the time stamp added to the MMT packet, thereby grasping the transmission delay Δd. The receiving apparatus starts displaying the MMT stream at time Tp+Δd obtained by adding the transmission delay Δd to the presentation time Tp represented by the time stamp added to the SI packet. 
     However, a delay may be caused by the multiplexing processing of the multiplexing apparatus, or the like. If the MMT packet cannot arrive at the presentation time Tp+Δd due to the delay caused by the multiplexing processing or the like, that is, in a buffer underflow state, display of the MMT stream cannot be started. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the functional arrangement of a broadcasting system provided with a multiplexing apparatus and a receiving apparatus according to the first embodiment. 
         FIG. 2  is a syntax chart showing an example of an MPU_timestamp_descriptor added to an MMT packet output from the multiplexing apparatus shown in  FIG. 1 . 
         FIG. 3  is a block diagram showing the functional arrangement of the multiplexing apparatus shown in  FIG. 1 . 
         FIG. 4  is a flowchart performed when the multiplexing apparatus shown in  FIG. 3  updates the output time and writes the delay amount of the presentation time. 
         FIG. 5  is a block diagram showing the functional arrangement of the receiving apparatus shown in  FIG. 1 . 
         FIG. 6  is a flowchart performed when the receiving apparatus shown in  FIG. 5  sets the adjustment amount of the presentation time of a video. 
         FIG. 7  is a schematic diagram showing a packet output time, a packet reception time, and a presentation time. 
         FIG. 8  is a syntax chart showing another example of the “MPU_timestamp_descriptor” shown in  FIG. 2 . 
         FIG. 9  is a syntax chart showing an example of an MPU presentation time offset descriptor in a case in which the MPU_timestamp_descriptor includes the information shown in  FIG. 8 . 
         FIG. 10  is a syntax chart showing another example of the MPU presentation time offset descriptor shown in  FIG. 9 . 
         FIG. 11  is a syntax chart showing an MP table that stores the MPU_timestamp_descriptor or the MPU presentation time offset descriptor. 
         FIG. 12  is a block diagram showing the functional arrangement of a broadcasting system provided with a receiving apparatus according to the second embodiment. 
         FIG. 13  is a block diagram showing the functional arrangement of the receiving apparatus shown in  FIG. 12 . 
         FIG. 14  is a flowchart performed when the receiving apparatus shown in  FIG. 13  sets the adjustment amount of the presentation time of a video. 
         FIG. 15  is a schematic diagram showing the packet output times, the packet reception times, and the presentation times of MMT packets output from pieces of transmission equipment shown in  FIG. 12 . 
         FIG. 16  is a block diagram showing another functional arrangement of the receiving apparatus shown in  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to an embodiment, a multiplexing apparatus includes processing circuitry. The processing circuitry multiplexes a plurality of MMT packets including at least one MMT packet to which first output time information representing a first output time at which the MMT packet is output from another apparatus and presentation time information representing a presentation time at which an accessible data unit formed from a payload is displayed are added. The processing circuitry rewrites the first output time information to second output time information representing a second output time at which the MMT packet is output. The processing circuitry adds a time necessary to multiplex the plurality of MMT packets to the presentation time represented by the presentation time information as a delay time, and outputs the MMT packet multiplexed by the packet multiplexing unit. 
     The embodiments will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a block diagram showing an example of the functional arrangement of a broadcasting system provided with a multiplexing apparatus and a receiving apparatus according to the first embodiment. The broadcasting system shown in  FIG. 1  includes transmission equipment  10  and a receiving apparatus  20 . The transmission equipment  10  transmits an MMT (MPEG Multimedia Transport) stream. The transmitted MMT stream arrives at the receiving apparatus  20  via a transmission channel such as a broadcasting network. The receiving apparatus  20  receives the MMT stream. 
     The transmission equipment  10  includes a video sending apparatus  11 , an encoding apparatus  12 , a multiplexing apparatus  13 , and a transmitting apparatus  14 . 
     The video sending apparatus  11  includes, for example, a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array) that executes predetermined processing under the control of the CPU, and a storage memory used to store data. Note that the video sending apparatus  11  may include an LSI (Large-Scale Integration) in place of the FPGA. The video sending apparatus  11  may execute predetermined processing by software processing of the CPU. The video sending apparatus  11  indicates, for example, an image capturing apparatus such as a camera and a server for archiving video/audio data. The video sending apparatus  11  outputs the video/audio data to the encoding apparatus  12 . 
     The encoding apparatus  12  includes, for example, a CPU, an FPGA that executes predetermined processing under the control of the CPU, and the like. Note that the encoding apparatus  12  may include an LSI in place of the FPGA. The encoding apparatus  12  may execute predetermined processing by software processing of the CPU. The encoding apparatus  12  encodes the video/audio data supplied from the video sending apparatus  11  in accordance with a protocol corresponding to MMT, thereby converting the video/audio data into an MMT packet. 
     The MMT packet includes a packet including video/audio data and an SI (Service Information) packet. The SI packet includes MMT configuration information. The MMT configuration information is information about the configuration of an MMT packet including the configuration of program information and video/audio data. A time stamp representing a presentation time Tp of an MPU (Media Processing Unit) formed from the payload of the MMT packet is added to the SI packet. The encoding apparatus  12  outputs the MMT packet to the multiplexing apparatus  13 . The encoding apparatus  12  adds a time stamp representing an output time Tt 1  to the MMT packet to be output. 
     A “MPU_timestamp_descriptor” representing the presentation time Tp is defined as in, for example,  FIG. 2 . The “MPU_timestamp_descriptor” shown in  FIG. 2  is provided with a syntax element capable of writing a delay amount to be described later, for example, 
     “mpu_presentation_time_offset”. 
     The multiplexing apparatus  13  includes, for example, a CPU, an FPGA that executes predetermined processing under the control of the CPU, and the like. The multiplexing apparatus  13  implements functions shown in  FIG. 3  by causing the CPU to execute functions designed by the FPGA.  FIG. 3  is a block diagram showing an example of the functional arrangement of the multiplexing apparatus  13  shown in  FIG. 1 . The multiplexing apparatus  13  shown in  FIG. 3  implements the functions of a packet multiplexing unit  131 , a sending time setting unit  132 , and a delay amount setting unit  133 . Note that the multiplexing apparatus  13  may include an LSI in place of the FPGA, thereby implementing the functions shown in  FIG. 3 . The multiplexing apparatus  13  may implement the functions shown in  FIG. 3  by software processing of the CPU. 
     The packet multiplexing unit  131  multiplexes MMT packets output from the encoding apparatus  12 . Note that in  FIG. 1 , the multiplexing apparatus  13  is configured to multiplex MMT packets output from the single encoding apparatus  12 . However, the multiplexing apparatus  13  may receive a plurality of MMT packets output from encoding apparatuses of different media. 
     The sending time setting unit  132  acquires an output time Tt 2  to output the multiplexed MMT packet to the transmitting apparatus  14  in accordance with the NTP (Network Time Protocol). The sending time setting unit  132  rewrites the output time Tt 1  written to the time stamp of the MMT packet multiplexed by the packet multiplexing unit  131  to the acquired output time Tt 2 . 
     The delay amount setting unit  133  records a delay amount Δt unique to the multiplexing apparatus  13  in advance. The delay amount Δt is, for example, a time needed for the multiplexing processing of the packet multiplexing unit  131 . The delay amount setting unit  133  adds the delay amount Δt to “mpu_presentation_time_offset” of the “MPU_timestamp_descriptor” of the SI packet. Accordingly, the presentation time changes to Tp+Δt. 
     Note that the delay amount setting unit  133  may calculate a delay caused by transmission from the encoding apparatus  12  to the multiplexing apparatus  13  and add the delay to the delay amount Δt. At this time, the packet multiplexing unit  131  acquires the reception time of the multiplexed MMT packet in accordance with the NTP. The delay amount setting unit  133  compares the time of reception of the MMT packet with the output time Tt 1 , thereby acquiring a transmission delay Δt′. The delay amount setting unit  133  writes a delay amount that is the sum of the delay amount Δt and the transmission delay Δt′ to “mpu_presentation_time_offset” of the “MPU_timestamp_descriptor” of the SI packet, and executes the following processing. 
     The transmitting apparatus  14  includes, for example, a CPU, an FPGA that executes predetermined processing under the control of the CPU, and the like. Note that the transmitting apparatus  14  may include an LSI in place of the FPGA. The transmitting apparatus  14  may execute predetermined processing by software processing of the CPU. The transmitting apparatus  14  performs transmission processing for the MMT packet output from the multiplexing apparatus  13 . The transmitting apparatus  14  transmits the MMT packet that has undergone the transmission processing as an MMT stream. 
       FIG. 4  is a flowchart performed when the multiplexing apparatus  13  shown in  FIG. 3  updates the output time and writes the delay amount of the presentation time. First, the packet multiplexing unit  131  receives MMT packets output from the encoding apparatus  12  (step S 41 ). The packet multiplexing unit  131  multiplexes the MMT packets (step S 42 ). 
     Next, the sending time setting unit  132  rewrites the output time Tt 1  written to the time stamp to the output time Tt 2  at which the sending time setting unit  132  outputs the MMT packet (step S 43 ). The delay amount setting unit  133  adds the delay amount Δt unique to the multiplexing apparatus  13  to “mpu_presentation_time_offset” of the “MPU_timestamp_descriptor” of the SI packet (step S 44 ). 
     The receiving apparatus  20  includes, for example, a CPU, an FPGA that executes predetermined processing under the control of the CPU, a storage memory used to store data, and the like. The receiving apparatus  20  implements functions shown in  FIG. 5  by causing the CPU to execute functions designed by the FPGA.  FIG. 5  is a block diagram showing an example of the functional arrangement of the receiving apparatus  20  shown in  FIG. 1 . The receiving apparatus  20  shown in  FIG. 5  implements the functions of a receiving unit  21 , a packet parsing control unit  22 , a packet header parsing unit  23 , an MMT-SI parsing unit  24 , a delay amount acquisition unit  25 , a presentation time control unit  26 , a payload extraction unit  27 , a buffer  28 , a decoder  29 , and a display unit  210 . Note that the receiving apparatus  20  may include an LSI in place of the FPGA, thereby implementing the functions shown in  FIG. 5 . The receiving apparatus  20  may implement the functions shown in  FIG. 5  by software processing of the CPU. 
     The receiving unit  21  receives an MMT stream that arrives via a transmission channel. The receiving unit  21  outputs the received MMT stream to the packet parsing control unit  22 . The receiving unit  21  also outputs the data of the received MMT stream to the packet header parsing unit  23 , the MMT-SI parsing unit  24 , or the payload extraction unit  27  in accordance with a control signal from the packet parsing control unit  22 . 
     That is, when a control signal representing that the data of the received MMT stream is the header of an MMT packet is received from the packet parsing control unit  22 , the receiving unit  21  outputs the data of the received MMT stream to the packet header parsing unit  23 . When a control signal representing that the MMT packet included in the received MMT stream is an SI packet is received from the packet parsing control unit  22 , the receiving unit  21  outputs the data of the received MMT stream to the MMT-SI parsing unit  24 . When a control signal representing that the MMT packet included in the received MMT stream is a packet including video/audio data is received from the packet parsing control unit  22 , the receiving unit  21  outputs the data of the received MMT stream to the payload extraction unit  27 . 
     The packet parsing control unit  22  controls the receiving unit  21 , the packet header parsing unit  23 , the MMT-SI parsing unit  24 , and the payload extraction unit  27  in accordance with the data structure of the received MMT stream. 
     That is, the packet parsing control unit  22  analyzes the received MMT stream, and upon determining that the received data is the header of an MMT packet, outputs, to the receiving unit  21 , a control signal representing that the data of the received MMT stream is the header of an MMT packet. The packet parsing control unit  22  outputs an instruction to the packet header parsing unit  23  to start analysis of supplied data. 
     If the packet header parsing unit  23  determines that the header is the header of an SI packet, the packet parsing control unit  22  outputs, to the receiving unit  21 , a control signal representing that the MMT packet included in the received MMT stream is an SI packet. The packet parsing control unit  22  outputs an instruction to the MMT-SI parsing unit  24  to start analysis of supplied data. The MMT-SI parsing unit  24  returns MMT configuration information that is information about the configuration of the MMT packet. 
     If the packet header parsing unit  23  determines that the header is the header of a packet including video/audio data, the packet parsing control unit  22  outputs, to the receiving unit  21 , a control signal representing that the MMT packet included in the received MMT stream is a packet including video/audio data. The packet parsing control unit  22  outputs an instruction to the payload extraction unit  27  to start extracting a payload from the MMT packet using the MMT configuration information interpreted by the MMT-SI parsing unit  24 . 
     Upon receiving an analysis start instruction from the packet parsing control unit  22 , the packet header parsing unit  23  analyzes the data of the header of the MMT packet output from the receiving unit  21 . Upon determining by the header analysis that the header is the header of an SI packet, the packet header parsing unit  23  outputs, to the packet parsing control unit  22 , a notification representing that the header is the header of an SI packet. Upon determining by the header analysis that the header is the header of a packet including video/audio data, the packet header parsing unit  23  outputs, to the packet parsing control unit  22 , a notification representing that the header is the header of a packet including video/audio data. 
     Upon receiving an analysis start instruction from the packet parsing control unit  22 , the MMT-SI parsing unit  24  analyzes the data of the SI packet output from the receiving unit  21 . The MMT-SI parsing unit  24  analyzes the data, thereby interpreting the MMT configuration information. The MMT-SI parsing unit  24  outputs the interpreted MMT configuration information to the packet parsing control unit  22 . 
     The delay amount acquisition unit  25  reads the presentation time Tp+Δt and the output time Tt 2  from the time stamp added to the SI packet. The delay amount acquisition unit  25  compares the output time Tt 2  with the reception time of the MMT packet acquired based on the NTP, and calculates a delay time Δd by the transmission channel. The delay amount acquisition unit  25  outputs Δt+Δd to the presentation time control unit  26  as the adjustment amount of the presentation time. 
     The presentation time control unit  26  controls the decoder  29  to start display at the time Tp+Δt+Δd considering the adjustment amount acquired by the delay amount acquisition unit  25 . 
     Upon receiving an extraction start instruction from the packet parsing control unit  22 , the payload extraction unit  27  analyzes the data of the packet including video/audio data output from the receiving unit  21  by referring to the MMT configuration information. The payload extraction unit  27  analyzes the data of the packet, thereby extracting the video/audio data (payload) from the packet. The payload extraction unit  27  causes the buffer  28  to hold the extracted payload. 
     Upon receiving a display start instruction from the presentation time control unit  26 , the decoder  29  reads the payload from the buffer  28 , and decodes the read payload. The decoder  29  causes the display unit  210  to display the decoded data. 
       FIG. 6  is a flowchart performed when the receiving apparatus  20  shown in  FIG. 5  sets the adjustment amount of the presentation time of a video. First, the receiving unit  21  receives an MMT stream that arrives via a transmission channel (step S 61 ). The receiving unit  21  outputs the data of the received MMT stream to the packet parsing control unit  22 . 
     The packet parsing control unit  22  analyzes the data of the received MMT stream, and determines that the data is the header of an MMT packet (step S 62 ). Upon determining that the received data is the header of an MMT packet, the packet parsing control unit  22  outputs a control signal representing that the received data is the header of an MMT packet to the receiving unit  21 , and also outputs an instruction to the packet header parsing unit  23  to start analysis of supplied data (step S 63 ). 
     The packet header parsing unit  23  receives the data of the header from the receiving unit  21 , and analyzes the received header (step S 64 ). Upon determining that the packet to which the received header is added is an SI packet, the packet header parsing unit  23  outputs a notification representing it to the packet parsing control unit  22  (step S 65 ). If the packet header parsing unit  23  determines that the header is the header of an SI packet, the packet parsing control unit  22  outputs, to the receiving unit  21 , a control signal representing that the packet included in the received MMT stream is an SI packet, and also outputs an instruction to the MMT-SI parsing unit  24  to start analysis of supplied data (step S 66 ). 
     Upon receiving the analysis start instruction from the packet parsing control unit  22 , the MMT-SI parsing unit  24  analyzes the data of the SI packet output from the receiving unit  21  (step S 67 ). The MMT-SI parsing unit  24  analyzes the data, thereby interpreting the MMT configuration information. 
     The delay amount acquisition unit  25  reads the presentation time Tp+Δt and the output time Tt 2  from the time stamp added to the SI packet. The delay amount acquisition unit  25  compares the output time Tt 2  with the reception time of the MMT packet acquired based on the NTP, and calculates the delay time Δd by the transmission channel. The delay amount acquisition unit  25  calculates Δt+Δd as the adjustment amount of the presentation time (step S 68 ). 
       FIG. 7  is a schematic diagram showing a packet output time, a packet reception time, and a presentation time. Referring to  FIG. 7 , an open rectangle indicates an MMT packet in a case in which the delay amount Δt is not generated, and a hatched rectangle indicates an MMT packet in a case in which the delay amount Δt is generated. Note that packet reorder is not considered in  FIG. 7 . As is apparent from  FIG. 7 , if a delay is generated by multiplexing processing, the receiving apparatus  20  delays the presentation time by the delay amount. That is, the receiving apparatus  20  can avoid a buffer underflow. 
     As described above, in the first embodiment, the multiplexing apparatus  13  includes the delay amount Δt associated with the multiplexing processing of the multiplexing apparatus  13  in the time stamp representing the presentation time Tp of the SI packet. The multiplexing apparatus  13  transmits the SI packet whose presentation time Tp includes the delay amount Δt to the receiving apparatus  20 . The multiplexing apparatus  13  can thus notify the receiving apparatus  20  of the delay amount Δt associated with the multiplexing processing. 
     Hence, the multiplexing apparatus  13  according to the first embodiment can cause the receiving apparatus  20  to display the MMT stream without causing a buffer underflow even if a processing delay occurs in the multiplexing apparatus  13 . 
     In the first embodiment, the receiving apparatus  20  causes the delay amount acquisition unit  25  to read the presentation time Tp+Δt and the output time Tt 2  from the time stamp added to the SI packet. The delay amount acquisition unit  25  compares the output time Tt 2  with the reception time of the MMT packet, and calculates the delay time Δd by the transmission channel. The delay amount acquisition unit  25  calculates Δt+Δd as the adjustment amount of the presentation time. The display unit  210  displays the video at the time Tp+Δt+Δd including the adjustment amount. The receiving apparatus  20  can thus display the video at the time including the transmission delay Δd and the delay Δt by the multiplexing processing of the multiplexing apparatus. 
     Hence, the receiving apparatus  20  according to the first embodiment can display the MMT stream without causing a buffer underflow even if a processing delay occurs in the multiplexing apparatus  13 . 
     Note that in the first embodiment, an example in which the encoding apparatus  12  defines the “MPU_timestamp_descriptor” shown in  FIG. 2  has been described. However, the present invention is not limited to this. For example, the encoding apparatus  12  need not provide “mpu_presentation_time_offset” in the descriptor. At this time, the multiplexing apparatus  13  writes the presentation time including the delay amount to “mpu_presentation_time”. 
     Instead of defining “mpu_presentation_time_offset”, a descriptor having, as elements, “mpu_presentation_time” representing the presentation time including the delay amount and “mpu_presentation_time_original” representing a presentation time that does not include the delay amount may be defined. At this time, the multiplexing apparatus  13  writes the presentation time before the delay amount is added to “mpu_presentation_time” and the presentation time including the delay amount to 
     “mpu_presentation_time_original”. 
     The encoding apparatus  12  may define a descriptor “mpu_presentation_time_offset_descriptor”, instead of expanding “mpu_presentation_time_offset” in “MPU_Timestamp_descriptor” shown in  FIG. 2 . In this case, the multiplexing apparatus  13  writes information about the delay amount to “mpu_presentation_time_offset_descriptor”. 
     More specifically, if “MPU_timestamp_descriptor” includes only the presentation time information of the MPU, as shown in  FIG. 8 , “MPU_presentation_time_offset_descriptor” shown in  FIG. 9  is used, and “mpu_presentation_time_offset” is transmitted to the receiving apparatus  20 . Note that the number X of bits of “mpu_presentation_time_offset” is 64 bits (32 integer second bits and 32 fraction second bits) at maximum, as in “mpu_presentation_time”. However, if the maximum value of the offset value can be defined in advance because of operation restrictions, for example, a total of 32 bits including 16 integer second bits and 16 fraction second bits may be set. If the maximum value of the offset value is smaller than 1 sec, only 16 or 32 fraction second bits may be set. 
     The data structure of “MPU_presentation_time_offset_descriptor” is not limited to the structure shown in  FIG. 9 . For example, since “mpu_presentation_time_offset” is assumed to rarely frequently change, a data structure configured to send only one offset, as shown in  FIG. 10 , may be used. The data structures shown in  FIGS. 9 and 10  may be provided with a reserved field in consideration of future expandability. 
       FIG. 11  is a syntax chart showing the data structure of “MP_table” that stores “MPU_Timestamp_descriptor”. “MPU_Timestamp_descriptor” is stored in “asset_descriptors_byte”. 
     “MPU_presentation_time_offset_descriptor” may also be stored in “asset_descriptors_byte”. If the offset value does not change for each asset such as a video or audio, “MPU_timestamp_descriptor” and “MPU_presentation_time_offset_descriptor” may be stored in “MP_table_descriptors_byte”. 
     The encoding apparatus  12  may write time information such as the presentation time not to the descriptor but to an application layer of a level higher than the MMT packet. In this case, the delay amount setting unit  133  of the multiplexing apparatus  13  adds an offset including the delay amount by multiplexing processing in the application layer. In this case, the receiving apparatus  20  further includes, for example, a UDP (User Datagram Protocol) parsing unit that interprets the contents of the upper application layer. 
     In the first embodiment, a case in which the receiving apparatus  20  provides the decoder  29  at the subsequent stage of the buffer  28  has been described as an example. However, the present invention is not limited to this. For example, the decoder  29  may be provided at the preceding stage of the buffer  28 . At this time, the buffer  28  holds video/audio data decoded by the decoder  29 . The presentation time control unit  26  controls the buffer  28  such that the video/audio data held by the buffer  28  is output at the time Tp+Δt+Δd. When the decoder  29  is provided at the subsequent stage of the buffer  28 , the capacity of the buffer  28  can be suppressed small. 
     Second Embodiment 
       FIG. 12  is a block diagram showing an example of the functional arrangement of a broadcasting system provided with a receiving apparatus according to the second embodiment. The broadcasting system shown in  FIG. 12  includes pieces of transmission equipment  10 - 1  and  10 - 2  and a receiving apparatus  30 . Each of the pieces of transmission equipment  10 - 1  and  10 - 2  transmits an MMT stream. The transmitted MMT stream arrives at the receiving apparatus  30  via a transmission channel such as a broadcasting network. The receiving apparatus  30  receives the MMT stream. 
     Note that the arrangement of the pieces of transmission equipment  10 - 1  and  10 - 2  is the same as that of the transmission equipment  10  according to the first embodiment. However, multiplexing processing by a multiplexing apparatus  13 - 1  of the transmission equipment  10 - 1  is executed by a delay amount of 0, and multiplexing processing by a multiplexing apparatus  13 - 2  of the transmission equipment  10 - 2  is executed by a delay amount Δt for the descriptive convenience. 
     Accordingly, the output time represented by a time stamp added to an MMT packet output from the multiplexing apparatus  13 - 1  is Tt 1 , and the presentation time represented by a time stamp added to an SI packet is Tp. On the other hand, the output time represented by a time stamp added to an MMT packet output from the multiplexing apparatus  13 - 2  is Tt 2  (that is, Tt 1 +Δt), and the presentation time represented by a time stamp added to an SI packet is Tp+Δt. 
     The receiving apparatus  30  includes, for example, a CPU, an FPGA that executes predetermined processing under the control of the CPU, a storage memory used to store data, and the like. The receiving apparatus  30  implements functions shown in  FIG. 13  by causing the CPU to execute functions designed by the FPGA.  FIG. 13  is a block diagram showing an example of the functional arrangement of the receiving apparatus  30  shown in  FIG. 12 . The receiving apparatus  30  shown in  FIG. 13  implements the functions of receiving units  21 - 1  and  21 - 2 , packet parsing control units  22 - 1  and  22 - 2 , packet header parsing units  23 - 1  and  23 - 2 , MMT-SI parsing units  24 - 1  and  24 - 2 , delay amount acquisition units  25 - 1  and  25 - 2 , presentation time control units  31 - 1  and  31 - 2 , payload extraction units  27 - 1  and  27 - 2 , buffers  28 - 1  and  28 - 2 , decoders  29 - 1  and  29 - 2 , and a display unit  210 . Note that the receiving apparatus  30  may include an LSI in place of the FPGA, thereby implementing the functions shown in  FIG. 13 . The receiving apparatus  30  may implement the functions shown in  FIG. 13  by software processing of the CPU. 
     The delay amount acquisition unit  25 - 1  acquires a delay amount from the SI packet included in the MMT packet output from the transmission equipment  10 - 1 . That is, the delay amount acquisition unit  25 - 1  reads the presentation time Tp and the output time Tt 1  from the time stamp added to the SI packet. The delay amount acquisition unit  25 - 1  compares the output time Tt 1  with the reception time of the MMT packet acquired based on the NTP, and calculates a delay time Δd 1  by the transmission channel. The delay amount acquisition unit  25 - 1  outputs Δd 1  to the presentation time control units  31 - 1  and  31 - 2  as the adjustment amount of the presentation time. 
     The delay amount acquisition unit  25 - 2  acquires a delay amount from the SI packet included in the MMT packet output from the transmission equipment  10 - 2 . That is, the delay amount acquisition unit  25 - 2  reads the presentation time Tp+Δt and the output time Tt 2  from the time stamp added to the SI packet. The delay amount acquisition unit  25 - 2  compares the output time Tt 2  with the reception time of the MMT packet acquired based on the NTP, and calculates a delay time Δd 2  by the transmission channel. The delay amount acquisition unit  25 - 2  outputs Δt+Δd 2  to the presentation time control units  31 - 1  and  31 - 2  as the adjustment amount of the presentation time. 
     The presentation time control unit  31 - 1  receives the adjustment amounts of the presentation time output from the delay amount acquisition units  25 - 1  and  25 - 2 . The presentation time control unit  31 - 1  compares the acquired adjustment amounts, and selects the maximum adjustment amount. The presentation time control unit  31 - 1  controls the decoder  29 - 1  to start display at time considering the selected adjustment amount. 
     That is, the presentation time control unit  31 - 1  compares the adjustment amount Δd 1  output from the delay amount acquisition unit  25 - 1  with the adjustment amount Δt+Δd 2  output from the delay amount acquisition unit  25 - 2 , and determines that the adjustment amount Δt+Δd 2  is larger. The presentation time control unit  31 - 1  selects the adjustment amount Δt+Δd 2 . The presentation time control unit  31 - 1  controls the decoder  29 - 1  to start display at time Tp+Δt+Δd 2  considering the selected adjustment amount. 
     The presentation time control unit  31 - 2  receives the adjustment amounts of the presentation time output from the delay amount acquisition units  25 - 1  and  25 - 2 . The presentation time control unit  31 - 2  compares the acquired adjustment amounts, and selects the maximum adjustment amount. The presentation time control unit  31 - 2  controls the decoder  29 - 2  to start display at time considering the selected adjustment amount. 
     That is, the presentation time control unit  31 - 2  compares the adjustment amount Δd 1  output from the delay amount acquisition unit  25 - 1  with the adjustment amount Δt+Δd 2  output from the delay amount acquisition unit  25 - 2 , and determines that the adjustment amount Δt+Δd 2  is larger. The presentation time control unit  31 - 1  selects the adjustment amount Δt+Δd 2 . The presentation time control unit  31 - 2  controls the decoder  29 - 2  to start display at time Tp+Δt+Δd 2  considering the decided adjustment amount. 
       FIG. 14  is a flowchart performed when the receiving apparatus  30  shown in  FIG. 13  sets the adjustment amount of the presentation time of a video. The receiving units  21 - 1  and  21 - 2 , the packet parsing control units  22 - 1  and  22 - 2 , the packet header parsing units  23 - 1  and  23 - 2 , and the MMT-SI parsing units  24 - 1  and  24 - 2  execute the processes of steps S 61  to S 67  shown in  FIG. 6 . 
     After step S 67 , the delay amount acquisition unit  25 - 1  reads the presentation time Tp and the output time Tt 1  from the time stamp added to the SI packet. The delay amount acquisition unit  25 - 1  calculates the delay time Δd 1  by the transmission channel from the output time Tt 1  and the reception time of the MMT packet. The delay amount acquisition unit  25 - 1  obtains Δd 1  as the adjustment amount of the presentation time. The delay amount acquisition unit  25 - 2  reads the presentation time Tp+Δt and the output time Tt 2  from the time stamp added to the SI packet. The delay amount acquisition unit  25 - 2  calculates the delay time Δd 2  by the transmission channel from the output time Tt 2  and the reception time of the MMT packet. The delay amount acquisition unit  25 - 2  obtains Δt+Δd 2  as the adjustment amount of the presentation time (step S 141 ). 
     The presentation time control units  31 - 1  and  31 - 2  compare the adjustment amount Δd 1  calculated by the delay amount acquisition unit  25 - 1  with the adjustment amount Δt+Δd 2  calculated by the delay amount acquisition unit  25 - 2 , and selects the adjustment amount Δ 6 +Δd 2  of the larger delay amount as the adjustment amount of the presentation time (step S 142 ). 
       FIG. 15  is a schematic view showing the packet output times, the packet reception times, and the presentation times of MMT packets output from the pieces of transmission equipment  10 - 1  and  10 - 2  shown in  FIG. 12 . Referring to  FIG. 15 , an open rectangle indicates an MMT packet output from the transmission equipment  10 - 1 , and a hatched rectangle indicates an MMT packet output from the transmission equipment  10 - 2 . Note that packet reorder is not considered in  FIG. 15 . As is apparent from  FIG. 15 , if there is a difference between times needed for multiplexing processing between the transmission equipment  10 - 1  and the transmission equipment  10 - 2 , the receiving apparatus  30  adjusts the presentation time of the shorter delay time to the presentation time of the longer delay time. That is, the receiving apparatus  30  can adjust the presentation time of the output MMT packet to the time Tp+Δt+Δd 2 . 
     As described above, in the second embodiment, the multiplexing apparatus  13 - 2  includes the delay amount Δt associated with the multiplexing processing of the multiplexing apparatus  13 - 2  in the time stamp representing the presentation time Tp of the SI packet. The multiplexing apparatus  13 - 2  transmits the SI packet whose presentation time Tp includes the delay amount Δt to the receiving apparatus  30 . The multiplexing apparatus  13 - 2  can thus notify the receiving apparatus  30  of the delay amount Δt associated with the multiplexing processing. 
     In the second embodiment, the receiving apparatus  30  causes the delay amount acquisition unit  25 - 1  to calculate Δd 1  as the adjustment amount of the presentation time from the presentation time Tp and the output time Tt 1  represented by the time stamp added to the SI packet. The delay amount acquisition unit  25 - 2  calculates Δt+Δd 2  as the adjustment amount of the presentation time from the presentation time Tp+Δt and the output time Tt 2  represented by the time stamp added to the SI packet. The presentation time control units  31 - 1  and  31 - 2  compare the adjustment amount Δd 1  output from the delay amount acquisition unit  25 - 1  with the adjustment amount Δt+Δd 2  output from the delay amount acquisition unit  25 - 2 , and decides the adjustment amount Δt+Δd 2  of the larger delay amount as the adjustment amount of the receiving apparatus  30 . 
     As shown in the second embodiment, in a case in which a plurality of pieces of transmission equipment exist, even if the delay amount caused by the multiplexing processing is added to the time stamp for each multiplexing apparatus provided in the transmission equipment, the delay amounts are different. For this reason, even if the receiving apparatus can adjust the delay amount, the presentation times cannot be synchronized between the pieces of transmission equipment as long as the delay amount is independently processed for each transmission equipment. According to the second embodiment, the presentation time control units  31 - 1  and  31 - 2  compare the delay amount of the MMT stream transmitted from the transmission equipment  10 - 1  with the delay amount of the MMT stream transmitted from the transmission equipment  10 - 2 , and control the decoders  29 - 1  and  29 - 2  using the larger one of the delay amounts. Hence, the receiving apparatus  30  can adjust the delay amounts even if there exist a plurality of pieces of transmission equipment. 
     Hence, the receiving apparatus  30  according to the second embodiment can display the MMT streams output from the pieces of transmission equipment  10 - 1  and  10 - 2  in synchronism even if the multiplexing apparatuses  13 - 1  and  13 - 2  have different processing delays. 
     Note that in the second embodiment, an example in which the receiving apparatus  30  has the arrangement shown in  FIG. 13  has been described. However, the present invention is not limited to this. For example, the receiving apparatus  30  may implement components shown in  FIG. 16  by causing the CPU to execute functions designed by the FPGA. According to  FIG. 16 , the receiving apparatus  30  implements the functions of the receiving units  21 - 1  and  21 - 2 , the packet parsing control units  22 - 1  and  22 - 2 , the packet header parsing units  23 - 1  and  23 - 2 , the MMT-SI parsing units  24 - 1  and  24 - 2 , the delay amount acquisition units  25 - 1  and  25 - 2 , a comparison unit  32 , a presentation time control unit  33 , the payload extraction units  27 - 1  and  27 - 2 , the buffers  28 - 1  and  28 - 2 , the decoders  29 - 1  and  29 - 2 , and the display unit  210 . 
     The comparison unit  32  receives the adjustment amounts of the presentation time output from the delay amount acquisition units  25 - 1  and  25 - 2 . The comparison unit  32  compares the acquired adjustment amounts, and selects the maximum adjustment amount. The comparison unit  32  outputs the selected adjustment amount to the presentation time control unit  33 . 
     The presentation time control unit  33  controls the decoders  29 - 1  and  29 - 2  to start display at time considering the adjustment amount selected by the comparison unit  32 . 
     In the second embodiment, a case in which the receiving apparatus  30  provides the decoders  29 - 1  and  29 - 2  at the subsequent stages of the buffers  28 - 1  and  28 - 2  has been described as an example. However, the present invention is not limited to this. For example, the decoders  29 - 1  and  29 - 2  may be provided at the preceding stages of the buffers  28 - 1  and  28 - 2 . At this time, the buffers  28 - 1  and  28 - 2  hold video/audio data decoded by the decoders  29 - 1  and  29 - 2 . The presentation time control units  31 - 1  and  31 - 2  control the buffers  28 - 1  and  28 - 2  such that the video/audio data held by the buffers  28 - 1  and  28 - 2  are output at the time Tp+Δt+Δd 2  of the larger delay amount. When the decoders  29 - 1  and  29 - 2  are provided at the subsequent stages of the buffers  28 - 1  and  28 - 2 , the capacities of the buffers  28 - 1  and  28 - 2  can be suppressed small. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of examples only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The appended claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.