Re: [FFmpeg-devel] what AVCodecID to use for copying full vanc data between .mxf and .mcc

["Tomas Härdin" <git@haerdin.se>]

tis 2025-07-22 klockan 13:56 -0700 skrev Jacob Lifshay:
> On July 22, 2025 5:21:24 AM PDT, "Tomas Härdin" <git@haerdin.se> 
> > * combining 436M and video essence to a full frame for playout
> iirc ffmpeg architecturally doesn't support merging a 608 stream into
> video side data since bitstream filters only have one input and
> avframe filters don't support subtitles. I've had to work around that
> with custom code in casparcg. 436m data is similar.

Perhaps I should have made it clear that I'm just spitballing what kind
of workflows we should keep in mind with this stuff. I'm not suggesting
we need to add support for everything right away. Just that we should
take steps toward a sane architecture for all this stuff. I'm not sure
what that would be though
> > 

> > > * add a new AVCodecID for mxf vbi_vanc_smpte_436M
> > > * change the muxers/demuxers to be able to use
> > > AV_CODEC_ID_SMPTE_KLV
> > > or AV_CODEC_ID_SMPTE_2038 (they hold the full vanc packets,
> > > right?)
> > 
> > Having key and length as part of the "essence" for these types of
> > streams sounds wrong and cursed. Shouldn't we do the same thing we
> > do
> > for audio and video, and convert either to some common format?
> 
> sure, for now I've picked 436m as the common format and left other
> vanc formats <-> 436m bitstream filters for others to implement.
> 
> > Otherwise, wouldn't we need to write BSFs for the outer product of
> > every type of ANC "codec"?
> 
> technically you can chain bsfs using av_bsf_list_finalize so we just
> have to support every anc codec <-> 436m. so when those eventually
> get implemented by someone else you can do AV_CODEC_ID_SMPTE_KLV ->
> AV_CODEC_ID_SMPTE_2038 via using 436m as an intermediate format.

Oh yeah that could work, assuming 436m is the most capable. Which it
is, last time I looked, since it support HANC and both 8-bit and 1-bit
data. It might require the right UL in mxfenc as you say

/Tomas
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