[Matroska-devel] MVC codec in Matroska container

Steve Lhomme slhomme at matroska.org
Sat Dec 8 15:37:14 CET 2012


That sounds good to me. Hopefully there is no decoder that assumes the
size of the last PPS is the size of the remaining CodecPrivate, which
would currently work by luck. That seems unlikely though, as the same
mechanism is probably applied with MP4 as well.

So I'm for adding new info to CodecPrivate, in a backward and forward
compatible way. Which what you all proposed seem to be.

Steve

On Sat, Dec 8, 2012 at 3:31 PM, Moritz Bunkus <moritz at bunkus.org> wrote:
> Hey,
>
> On Sat, Dec 8, 2012 at 3:25 PM, Steve Lhomme <slhomme at matroska.org> wrote:
>
>> Does the current AVC codec private include size boundaries ?
>
> It does, more or less. The format is as follows:
>
> - the first six bytes contain reserved bytes and the information how
> big size fields are in this AVC track (2, 3 or 4 bytes, usually 4)
> - byte 7 contains the number of SPS units following
> - each SPS unit consists of a size field (in the length mentioned in
> step above) and the SPS content (specified by the size field directly
> preceding it)
> - afterwards another bye containing the number of PPS units following
> - each PPS unit consists of a size field (in the length mentioned in
> step above) and the SPS content (specified by the size field directly
> preceding it)
>
> So yes, conforming decoders should stop decoding after the AvcC even
> if the CodecPrivate contains more data than indicated by those 6 + 1 +
> (total size of SPS units & their size fields) + 1 + (total size of PPS
> units & their size fields).
>
> The current proposal is to add similar structures at the end: 1. size
> field (number of bytes of this size field is again equal to the length
> indicated in those very first 7 bytes); 2. four-byte
> identification/type field (something like a FourCC); 3. content
>
>> If so it could be extended.
>
> I agree, it can, and I think I prefer it slightly over a CodecPrivateEx.
>
> Kind regards,
> mosu
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-- 
Steve Lhomme
Matroska association Chairman


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