Transmission apparatus, transmission method, reception apparatus, and reception method

1. A transmission apparatus comprising:

a video encoder that generates a video stream formed with a video packet having coded image data in a payload;

a subtitle encoder that generates a subtitle stream formed with a subtitle packet having subtitle information in a payload;

a multiplexer that generates a multiplexed stream including the video stream and the subtitle stream; and

a transmission device that transmits the multiplexed stream,

wherein the subtitle encoder is configured to

obtain a timestamp from the video packet as a target timestamp of a random access position,

obtain a subtitle timestamp on a basis of the target timestamp,

perform accuracy conversion on a stored subtitle start time, and

insert the subtitle timestamp and a converted timestamp resulting from the accuracy conversion into a timestamp insertion position of a header of the subtitle packet, and

wherein the multiplexer arranges the subtitle packet at a random access position, on the basis of the subtitle timestamp.

2. The transmission apparatus according to claim 1 , wherein the subtitle encoder inserts the converted timestamp as a unique timestamp indicating a display time of a subtitle into one of the header and a payload of the subtitle packet.

3. The transmission apparatus according to claim 2 ,

wherein the multiplexer inserts identification information indicating that the unique timestamp has been inserted into the subtitle packet, into the multiplexed stream.

4. The transmission apparatus according to claim 3 , wherein information indicating an insertion position is added to the identification information.

5. The transmission apparatus according to claim 1 ,

wherein the subtitle information is text information of a subtitle of a predetermined format having display timing information.

6. The transmission apparatus according to claim 5 ,

wherein the text information of the subtitle of the predetermined format is one of Timed Text Markup Language (TTML) and a derived format of the TTML.

7. The transmission apparatus according to claim 1 ,

wherein each of the video packet and the subtitle packet is a PES packet, and

the multiplexed stream is an MPEG2 transport stream.

8. A transmission method comprising:

generating, by a video encoder, a video stream formed with a video packet having coded image data in a payload;

generating, by a subtitle encoder, a subtitle stream formed with a subtitle packet having subtitle information in a payload;

generating, by a multiplexer, a multiplexed stream including the video stream and the subtitle stream; and

transmitting, by a transmission device, the multiplexed stream by a transmission unit,

wherein the subtitle encoder is configured to

obtain a timestamp from the video packet as a target timestamp of a random access position,

obtains a subtitle timestamp on a basis of the target timestamp,

perform accuracy conversion on a stored subtitle start time, and

insert the subtitle timestamp and a converted timestamp resulting from the accuracy conversion into a timestamp insertion position of a header of the subtitle packet,

wherein the multiplexer arranges the subtitle packet at a random access position, on the basis of the subtitle timestamp.

9. A reception apparatus comprising a receiver that receives a multiplexed stream including a video stream formed with a video packet having coded image data in a payload and including a subtitle stream formed with a subtitle packet having subtitle information in a payload,

the subtitle packet being arranged at a random access position in the received multiplexed stream, wherein the random access position is based on a target timestamp obtained from the video packet of the video stream,

the reception apparatus further comprising processing circuitry that retrieves the subtitle packet from the multiplexed stream together with the video packet at the random access position and that performs subtitle display processing.

10. The reception apparatus according to claim 9 ,

wherein the converted timestamp having a value equal to or close to a value as a value of a timestamp inserted into a timestamp insertion position of a header of the video packet at the random access position, is inserted into a timestamp insertion position of the header of the subtitle packet,

a second timestamp indicating a display time of the subtitle is inserted into one of the header and the payload of the subtitle packet, and

the processing circuitry performs, in a normal reproduction mode, subtitle display processing with reference to the second timestamp.

11. The reception apparatus according to claim 10 ,

wherein identification information indicating that the second timestamp has been inserted into the subtitle packet is inserted into the multiplexed stream, and

the processing circuitry extracts the second timestamp from the subtitle packet on the basis of the identification information and uses the second timestamp.

12. A reception method comprising a reception step of receiving, by a receiver, a multiplexed stream including a video stream formed with a video packet having coded image data in a payload and including a subtitle stream formed with a subtitle packet having subtitle information in a payload,

the subtitle packet being arranged at a random access position in the multiplexed stream, wherein the random access position is based on a target timestamp obtained from the video packet of the video stream,

the reception method further comprising retrieving the subtitle packet from the multiplexed stream together with the video packet at the random access position and performing subtitle display processing by processing circuitry.