[FFmpeg-devel] Captions SCC

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Tom
> Vaughan
> Sent: Friday, February 7, 2025 7:36 PM
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] Captions SCC
>
> Soft Works said... "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."

Hi Tom,

> You're confusing subtitles with closed captions. 

No.

> Subtitles are text that is composited into the video.

No.

> CEA-708 closed captions are
> carried as metadata in SEI NAL units, muxed into the elementary video
> stream.

I wouldn't call this "muxing" but that's not worth a debate.
(you might want to spend a thought on why it's called "elementary stream")


I said "it is also not possible to add CCs at the muxer level".

By that I mean "muxing" in ffmpeg terminology which is unambiguous.

sw


> 
> On 2/6/25, 11:48 PM, "ffmpeg-devel on behalf of Soft Works" <ffmpeg-
> devel-bounces at ffmpeg.org <mailto:ffmpeg-devel-bounces at ffmpeg.org> on
> behalf of softworkz-at-hotmail.com at ffmpeg.org <mailto:softworkz-at-
> hotmail.com at ffmpeg.org>> wrote:
> 
> 
> > -----Original Message-----
> > From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org <mailto:ffmpeg-
> devel-bounces at ffmpeg.org>> On Behalf Of
> > Devlist Archive
> > Sent: Friday, February 7, 2025 6:13 AM
> > To: FFmpeg development discussions and patches <ffmpeg-
> > devel at ffmpeg.org <mailto:devel at ffmpeg.org>>
> > Subject: Re: [FFmpeg-devel] Captions SCC
> >
> 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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