Re: [Cellar] AV1 mapping Matroska

2018-07-02 12:34 GMT+02:00 Michael Niedermayer <michael@niedermayer.cc>:
> Hi
>
> On Mon, Jul 02, 2018 at 09:47:45AM +0200, Moritz Bunkus wrote:
>> Hey,
>>
>> > Looking at the term "coded video sequence" (CVS) in other codecs (H.264
>> > and H.265) it seems it's a common term. And for those codec one Segment
>> > correspond to one CVS, with the parameters of that CVS stored in the
>> > CodecPrivate (SPS + PPS for H.264 for example). So we should probably go
>> > in that simple way.
>>
>> I have quite a lot of h.264 samples here, mainly M2TS from DVB, where
>> SPS/PPS change mid-stream, often multiple times. For such files the first
>> occurrences of SPS/PPS make up the AvcC in CodecPrivate, but all key frames
>> are still prefixed with the currently active SPS/PPS — because that's the
>> only way to signal that stuff has actually changed.
>
> IMHO All SPS/PPS should be in the "global header" (CodecPrivate) which the
> global header applies to, not just the first.
> This way an application can know all resolutions, aspect ratios and so on
> from just the header without the need to scan through all random access
> points.

My understanding is that it's how it's done in MP4:

"Each AVC sample entry, which contains the AVC video stream decoder
specific information, includes a group of SPSs and PPSs. This group of
parameter sets functions much like a codebook. Each parameter set has
an identifier, and each slice references the parameter set it was
coded against using the parameter set's identifier."

I have to check but I don't think Sequence Headers OBUs have
identifiers like that in AV1.

By the way, this is one mapping for V_AV1. There could be other AV1
mapping in Matroska where there is no CodecPrivate and there could be
multiple coded video sequences in it. But it would require the use of
CodecState and CueCodecState which is currently not an option for
WebM. So for now I will concentrate on a single coded video sequence.
And if needed in the future we can do a different one.

> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Those who are too smart to engage in politics are punished by being
> governed by those who are dumber. -- Plato
>
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-- 
Steve Lhomme
Matroska association Chairman