On 2021-02-23 02:46, Gyan Doshi wrote:
On 23-02-2021 12:40 pm, Mark Filipak (ffmpeg) wrote:
On 2021-02-23 01:38, Carl Zwanzig wrote:
You missed mentioning the program clock reference (PCR) of the -ts. -And- many references to PTS
directly say that it's contained in a -ts (which if the -ts contains a -ps, is correct).
The answers are in a GIF illustration (not text) in the H.262 spec, so searching the PDF doesn't
find any hits. From the GIF,
In the encoder:
STC (System Time Clock) is 27MHz.
PTC is (STC counter value)+(fixed buffer delay) that's written into the PS at the start of each
frame. [1]
PCR (Program Clock Reference) is (STC counter value) that's written into the TS (in the muxer)
every 100ms.
In the decoder:
STC (System Time Clock) is 27MHz.
There are no counters in the decoder. There's a STC-PTS comparator to signal new frames and a
STC-PCR comparator to control the STC's phase lock loop.
[1] Why the GIF leaves out the by-300 PTS divider is a mystery, but I know it exists (i.e., PTS
resolution = 1/(27MHz/300).
Our demuxer/muxer only read the top 33-bits (so TB is set at 90kHz). The bottom 9-bits are ignored,
last time I checked. There's 6 bits of padding in between.
I can scarcely overestimate how important this is.
Please clarify: ffmpeg ignores the bottom 9 bits of the PTS?
BTW, the PTS is part of the PES_HEADER_EXTENSION. A PES_HEADER occurs in each sector (2048 bytes) of
the TS, but a PES_HEADER_EXTENSION occurs only at the beginning of each frame, so I consider PTS
part of the presentation stream, not the transport stream. Your mileage may vary and opposing
opinions are entertained (though wrong).
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