Re: [FFmpeg-devel] Captions SCC

From: Devin Heitmueller <devin.heitmueller@ltnglobal.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] Captions SCC
Date: Fri, 7 Feb 2025 13:05:22 -0500
Message-ID: <CAHGibzEn5eofMBxVw80NfgwyyqidWi4fDuDWWP+gN82qvHEOjg@mail.gmail.com> (raw)
In-Reply-To: <CANJxsBnD7R29NeTHT4DTsk2eJmrsVa-FzP0uQ015QkYyp8OEKw@mail.gmail.com>

On Fri, Feb 7, 2025 at 11:42 AM Devlist Archive <devlist@rlb.org> wrote:
> As such, I may be able to work out an edit workflow by using RCWT to make a
> .bin file, using ccextractor to make an mcc file and importing into an edit
> suite for transcode.  The part I will still be missing is something to take
> the .ssc file output from Premiere and put it back in the .mp4 container.
> Embedding seems to be present for some forms of subtitles, but not for a
> proper captions file generated by MacCaption or Captionmaker which is
> software I am trying to avoid having to buy as I would much rather those
> funds go towards development.  One solution I guess would be to just
> require sidecar files for playout which I would prefer not to require.  I
> can look into those solutions off list.  MCC files or other formats that
> support 708 are the ideal, but 608 is all that is required.

For what it's worth, ffmpeg does have an MCC demuxer, but not a muxer.
Writing one though would be pretty easy (it's a relatively simple
format).  Probably the bigger issue is that internally ffmpeg tends to
strip out all the 708 when using the "subcc" mechanism, only
preserving the 608 tuples.

I've actually got code in the tree to handle framerate changes for
captions (the cc_fifo mechanism).  It works for CC within video
streams (e.g. user_data or SEI), but isn't implemented in the case
where you have C608 packets.  It might be possible to insert the
"cc_repack" filter and framerate conversion in the first part of the
command before sending the CC data to before handing off the data to
the subcc output.  That said, I've never tried it and would probably
have to play around with it to get the syntax right.

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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