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

[Devin Heitmueller <devin.heitmueller@ltnglobal.com>]

Hi Jake,


On Tue, Jul 8, 2025 at 12:12 AM Jacob Lifshay
<programmerjake-at-gmail.com@ffmpeg.org> wrote:
>
> I'm currently writing a .mcc muxer, it currently translates from eia-608/708 to full vanc packets before outputting a .mcc file:
> https://github.com/programmerjake/FFmpeg/tree/add-mcc-mux

I took a quick look at your branch.  So this is a good start, IMHO...

Note that I took a look at the MCC demuxer last year, and it's got a
bunch of issues where the parsing makes a bunch of assumptions (e.g.
doesn't filter out other VANC types which might be present in an MCC
such as AFD).  And it only extracts 608 (i.e. doesn't handle 708).
I'm mentioning this should you try using the MCC demuxer while
developing a muxer.  The demuxer would need some love before I would
trust it for anything in production.

> I want to add the ability to the mxf and mcc muxers/demuxers to keep the full vanc data when doing stream copies, what do you think is the best way to do that?
>
> * 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?)

I would stay away from KLV entirely.

The SMPTE 2038 standard does support all VANC data types, but support
in ffmpeg really is only oriented around passthrough (i.e. routing
2038 packets from an input TS to an output TS).  It currently doesn't
attempt to decode the 2038 payloads into something easier to work
with.  I've built stuff like bitstream filters that take in 2038
packets and use libklvanc to parse out the individual VANC sections,
but none of that is upstream (happy to send you links to where it can
be found in my public GitHub repo).  In other words, you might have
difficulty working with the structures if you have to deserialize them
and reserialize them when passing them between modules (although
libklvanc does technically support both).

> * use the mxf vbi_vanc_smpte_436M stream as is -- AV_CODEC_ID_NONE and with vbi_vanc_smpte_436M in the metadata

I can't speak to whether this would be a good idea.

> additionally, it'd be nice to be able to output a eia-608/708 stream to mxf, so that would either need a codec/filter of some sort to translate to full vanc data in whatever format the mxf muxer ends up supporting, or to have that translation built-in to the mxf muxer, like it is built-in to the mxf demuxer (with eia608_extract).

I've done this sort of thing with bitstream filters.  The BSF takes in
2038, extracts the 608, and outputs 608 packets.  You could do
something comparable for MXF.  Also, I set up the muxers to
automatically insert the BSF if needed, which makes it painless for
the user.

The 608/708 stuff is kind of a mess in terms of what is in those
payloads.  Some modules will expect 608 only, others will contain
tuples that include 708.  And there continues to be no easy way to go
back and forth between 608 packets and SEI data embedded within the
video stream (in either direction:  SEI to 608 packet streams, or 608
packet streams into SEI).

Devin

-- 
Devin Heitmueller, Senior Software Engineer
LTN Global Communications
o: +1 (301) 363-1001
w: https://ltnglobal.com  e: devin.heitmueller@ltnglobal.com
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