The presentation timestamp (PTS) is the timestamp metadata field in the MPEG transport stream or stream of MPEG programs used to achieve a separate stream-based synchronization of the program (eg Video, Audio, Text) when presented to the viewer. PTS is given in units related to the program's overall reference clock, Reference Program Clock (PCR) or System Clock Reference (SCR), which is also transmitted in the flow of transport or program flow.
Present time stamps have 90kHz resolution, perfect for presentation synchronization tasks. PCR or SCR has 27MHz resolution suitable for clock synchronization of whole set-top box with existing in ordinary remote encoder, including TV signal driving such as frame and time line synchronization, color sub-carrier, etc.
The decomposition of the base N stream is synchronized by adjusting the flow coding to the general master time base rather than by adjusting the one-stream encoding to match one stream. The master time base can be either an N clock decoder, a data source clock, or possibly several external clocks.
The flow of transport can contain several programs and each program can have its own time base. The time base of different programs in the transport flow may be different. Since the PTS applies to the decomposition of each base stream, they are inside the PES packet layer of both transport flow and program flow. End-to-end sync occurs when the encoder stores a time stamp at the time of capture, when the time stamp is propagated with the encoded data associated to the decoder, and when the decoder uses the timestamp to schedule the presentation.
The synchronization of the decoding system with the channel is achieved through the use of SCR in the program stream and by its analogue, PCR, in the transport flow. SCR and PCR are timestamps that encode time from the bit stream itself, and are derived from the same time base used for the PTS values ​​of the audio and video of the same program. Since each program can have its own time base, there is a separate PCR column for each program in the transport stream that contains multiple programs. In some cases it is possible for programs to share PCR fields.
Video Presentation timestamp
See also
- Pack base flow
- Audio to video sync
Maps Presentation timestamp
References
Source of the article : Wikipedia
0 Comments