Re: [FFmpeg-devel] Captions SCC

[Soft Works <softworkz-at-hotmail.com@ffmpeg.org>]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> Devlist Archive
> Sent: Friday, February 7, 2025 6:13 AM
> To: FFmpeg development discussions and patches <ffmpeg-
> devel@ffmpeg.org>
> Subject: Re: [FFmpeg-devel] Captions SCC
> 
> On Thu, Feb 6, 2025 at 4:57 AM Jack Lau <jacklau1222gm@gmail.com>
> wrote:
> 
> >
> >
> > > I have been absent from the list for a few years, so I would
> appreciate
> > it
> > > if someone could catch me up a bit.  I am needing to extract and
> embed
> > scc
> > > files with 608 captions.  I am pleased to see that transcoding
> without
> > > frame rate changes now preserves 608 intact, and there appear to
> be
> > > extraction and embed functions but they do seem to have bugs for
> my files
> > > at 1080p2997.  Are there any developers willing to take on a paid
> project
> > > to fix whatever is the issue?  Here are the commands I am working
> with.
> > >
> > > Embed:
> > > "C:\FFmpeg\ffmpeg7.1_2024-12-14\ffmpeg.exe" -i
> > > "C:\Users\Captions\AIM-2301_premiereDF.mp4" -i
> > > "C:\Captions\AIM-2301_premiereDF.mp4.scc" -map 0:v -map 0:a -map
> 1 -c:v
> > > copy -c:a copy -c:s mov_text -metadata:s:s:0 language=eng
> > > "C:\Captions\AIM-2301_premiereDFcopy.mp4"
> > >
> > > Extract:
> > > "C:\FFmpeg\ffmpeg7.1_2024-12-14\ffmpeg.exe" -f lavfi -i
> > >
> > "movie=\'C:\\Captions\\AIM-
> 2301_premiereDF_ffmpegEmbedscc.mp4\'"[out+subcc]
> > > -map 0:1 -c:s copy "C:\Captions\AIM-
> 2301_premiereDF_ffmpegEmbedscc.scc”
> > >
> >
> >
> > Hi,
> >
> > I’ve reviewed the issue with embedding and extracting 608 SCC
> captions at
> > 1080p2997 resolution and identified a few areas that might help
> resolve the
> > character duplication and data spill. Here's a summary of my
> findings:
> >
> > The current command uses -c:s mov_text, but SCC files may work
> better with
> > -c:s scc to preserve the format correctly.
> > The current command uses a filtergraph that might not map correctly
> for
> > SCC extraction. Instead, try simplifying the extraction command: -
> map 0:s:0
> > -c:s copy
> > Frame Rate Issues: Ensure the video frame rate and the SCC file
> frame rate
> > match. You might want to force a specific frame rate (e.g., -r
> 29.97).
> >
> > Let me know if you have further questions.
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel@ffmpeg.org
> > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

> Hi Jack,
> 
> Thanks for the suggestions.  Could you please tell me where I can get
> a
> build of ffmpeg that will work with the -c:s scc command?  That
> encoder
> doesn't seem to be in the release version I am working with.
> 
> It is slightly unclear to me how your suggestion for the extract
> command
> suggestion should be implemented.  All of my media files I am working
> with
> now are the same frame rate, but forcing a frame rate prior to
> embedding is
> probably a good idea.  I had assumed there were still bugs in the
> code for
> this, but it would be nice if extraction/embedding could work without
> having to  change more.
> 
> Zach


Hi Zack,

that message from "Jack" had confused me for a moment, but on re-reading it appears to be an AI response.
The content is total nonsense. There is no "SCC" encoder in ffmpeg, and if there was one, it wouldn't help much because the CC data needs to get into the video frames - so that it exists as input to the video encoder.
For the same reason, it is also not possible to add CCs at the muxer level. It always requires video encoding because the data needs to get into the video stream itself, so there's no way to get data from an SCC file into a video stream currently.

The only way in the ffmpeg architecture to get CC data encoded would be at the filtering level. The Subtitle Filtering patchset that I have submitted a while ago has a "splitcc" filter which has video as input and a video plus a subtitle pin/pad at the output side.
What would be needed is a reverse pendant like a "mergecc" filter with video and subtitles input - plus a CEA-608/708 encoder.

softworkz



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