[FFmpeg-devel] Re: [PATCH] av1_in_ts_v2 (PR #21307)

[James Almer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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On 1/12/2026 1:31 PM, Nicolas Gaullier via ffmpeg-devel wrote:
> On 12/28/25 19:45, Jun Zhao via ffmpeg-devel wrote:
>> PR #21307 opened by Jun Zhao (mypopydev)
>> URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21307
>> Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21307.patch
>>
>> Add functions to parse AV1 OBUs in MPEG-TS start code format
>> (0x000001 prefix). This is needed for AV1 streams from MPEG-TS
>> containers per AOM AV1 in MPEG-2 TS specification.
> 
> I have some questions around aligned PES and start codes; please correct 
> me if I am wrong.
> 
> Start codes: it seems to me current PR autodetects start codes, which 
> means if a stream miss them, it would still be successfully decoded. 
> This is possible because, additionally, AV1 requires aligned PES (which 

Where does the spec say that?

> is unusual for h2645 typically). Being able to handle non-conformant 
> files is nice until there are no downsides. The situation is maybe a 
> little bit tricky here since this format is not widespread, you may want 
> to be more carefull, check interoperability etc., and maybe you want to 
> be warned that "this file may not be supported outside of ffmpeg" ? It 

Why would we warn that? Demuxing has no need for any kind of warning 
like that. We're reading a file and trying to make sense of its 
contents. What other readers can or can't do is irrelevant.

> seems there is no "issue" in the other way (a stream which is not pes- 
> aligned would not be decodable since there is no "find_frame_end" in the 
> parser to split the packets), but anyway maybe it could be 

I already wrote an implementation for Temporal Unit assembly in 
av1_parser, but I'm waiting until all is said and done, and probably an 
actual sample is provided.

> an interesting opportunity to introduce pes alignment support in 
> mpegts ? If I understand correctly, it would allow disabling packet 
> repacking in some use cases (j2k for example: I just had a quick look 
> today since mpegts mandates pes alignment for it too).
> 
> Nicolas
> 
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