Re: [FFmpeg-devel] Captions SCC

From: Jack Lau <jacklau1222gm@gmail.com>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] Captions SCC
Date: Thu, 6 Feb 2025 20:57:12 +0800
Message-ID: <96807479-FC34-4BBB-8421-6F242CDDBD4D@gmail.com> (raw)
In-Reply-To: <CANJxsBnbiNqVFmWCFoewud9urmnKjpGN-EADUHRMR+i44+dpQQ@mail.gmail.com>

> 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.
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