[Cellar] Fwd: Update specification language: CodecPrivate element MUST be set for H264 in Matroska

[guest271314 <[e-mail]>]

---------- Forwarded message ---------
From: guest271314 <[e-mail]>
Date: Sun, Dec 27, 2020 at 8:31 AM
Subject: Re: [Cellar] Update specification language: CodecPrivate element
MUST be set for H264 in Matroska
To: Jerome Martinez <[e-mail]>


Do you mean that we should be even more clear in 2 places?
> - in CodecPrivate definition, something like CodecPrivate is mandatory
> if specified as such ("MUST") in the corresponding codec mapping
> specification.
> - in H.264 codec mapping definition, something like The CodecPrivate
> block MUST contain a AVCDecoderConfigurationRecord structure [...]


Yes. That is what the request for updating the standard/specification
states. Evidently that information (wording; language) was not clear enough
for Chrome authors when they implemented H264 encoding in Matroska
container for MediaRecorder.

Since your organization is the authority in this matter it would be helpful
to inform the Chrome authors of their omission of the CodecPrivate element
- otherwise nothing will change and users in the field will still not be
able to extract H264 tracks from the resulting Matroska file that Chrome
MediaRecorder implementation produces when mimeType is set to
'video/x-matroska;codecs=h264' or 'video/x-matroska;codecs=avc1'.

On Sun, Dec 27, 2020 at 8:15 AM Jerome Martinez <[e-mail]>
wrote:

> On 27/12/2020 16:33, guest271314 wrote:
> > Cure that by conspicuously and unambiguously including wording in the
> > standard/specification that " CodecPrivate element MUST be set for
> > H264 in Matroska".
>
> CodecPrivate in Matroska general specification is not mandatory, as this
> status depends on the coding format (mandatory for H.264, not mandatory
> for MPEG-2 etc).
>
> From
>
> https://github.com/ietf-wg-cellar/matroska-specification/blob/master/codec_specs.md#v_mpeg4isoavc
> "The Private Data contains a AVCDecoderConfigurationRecord structure,
> [...]"
> This is not the IETF "MUST" but seems clear (affirmative sentence) that
> CodecPrivate is mandatory in the case of the H.264 mapping.
>
> Do you mean that we should be even more clear in 2 places?
> - in CodecPrivate definition, something like CodecPrivate is mandatory
> if specified as such ("MUST") in the corresponding codec mapping
> specification.
> - in H.264 codec mapping definition, something like The CodecPrivate
> block MUST contain a AVCDecoderConfigurationRecord structure [...]
>
> Jérôme
>
>