Re: [FFmpeg-devel] [RFC]x264 avcc and related issue

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Zhao Zhili:
> There are multiple encoders which can output bitstream in avcc/hvcc format,
> e.g, x264, x265 and videotoolbox. This can improve performance depends on
> container format (no more ff_avc_parse_nal_units_buf).
> 
> The problem is these encoders output parameter sets directly, not contained
> in a complete AVC/HEVC configuration box. But muxers only expect
> extradata in
> annexb format, or a complete AVC/HEVC configuration box, not support such
> length+sps+length+pps format. The following command will output a broken
> file:
> 
> ./ffmpeg -i input.mp4 -an -c:v libx264 -x264-params annexb=0 broken.mp4
> 
> I want to fix this issue and improve the performance at the same time.
> 
> There are multiple options that I don't know how to make a choice.
> 
> 1. At the muxer level? It's easy and ugly. And there are corner case
> like 00 00 01 xx can be start code of annexb and size of avcc at the
> same time.
> 
> 2. A new bsf? It looks less useful outside of libavcodec. And encoder
> can't enable a bsf automatically.
> 
> 3. A specific helper like h26x_vcc.h? Can it be more general?
> 
> Any more suggestions?
> 

If we support a new packetization (even if it only affects extradata),
we would need to support it everywhere -- decoders and muxers, too. I
don't see an advantage or a need for a new packetization, as AFAIK all
containers with ISOBMFF packetization also use the ISOMBFF configuration
box. So I am against 1. and 2.
Implementing this inside lavc seems like the best approach; I don't know
whether a common helper for this will be useful: While these lists
certainly have a common pattern, there are subtle changes between them
which will probably make a common helper unsuitable.

- Andreas

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