[x264-devel] Re: Access Unit Delimiter

[Måns Rullgård]

"leon jorgunsen" <leon.jorgunsen at caramail.com> writes:

>> > I am using x264 + VLC to stream AVC video in MPEG-2 Transport
>> > Stream. x264 does not use Access Unit Delimiters (AUDs) to mark frame
>> > starts (or, at least, I have not found how to do it). However, the use
>> > of these NAL units is mandatory when embeddng AVC video streams in
>> > MPEG-2 systems (Ammendment 3 of MPEG-2 (2000)  part 1 recommendation).
>> 
>> My draft of that document doesn't mention this requirement.  Do you
>> have a later version?  Could I have a copy, please?
>> 
>
> Quoted from ISO/IEC 13818-1/2000/FDAM-3 (N5771):

Thanks, I've been sent a copy of the final draft.

> "2.14 Carriage of ITU-T Rec. H.264 | ISO/IEC 14496-10 Video
> The ITU-T Rec. H.264 | ISO/IEC 14496-10 coded data shall comply with
> the byte stream format defined in Annex B of ITU-T Rec. H.264 |
> ISO/IEC 14496-10, with the following constraints:
> * Each AVC access unit shall contain an access_unit_delimiter NAL Unit.

I've added an option for this.

> * Each byte stream NAL Unit containing the access unit delimiter
> contains one zero_byte preceding the start_code_prefix_one_3bytes,
> as required by ITU-T Rec. H.264 | ISO/IEC 14496-10.

I believe this to be the case.

> * Sequence and Picture Parameter Sets (SPS and PPS) shall be present
> within each AVC video stream carried in Transport and Program
> streams (Note that ITU-T Rec. H.264 | ISO/IEC 14496-10 allows the
> delivery of SPS and PPS by external means).

x264 always places the SPS/PPS in the video stream, AFAIK.

> * To provide display specific information such as aspect_ratio, it
> is strongly recommended that the each AVC video stream carries VUI
> messages with sufficient information to ensure that the decoded AVC
> video stream can be displayed correctly by receivers."

This is done, provided the caller supplies adequate information.

-- 
Måns Rullgård
mru at inprovide.com

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