[FFmpeg-devel] Status and Plans for Subtitle Filters

[Paul B Mahol]

On 2/14/20, Soft Works <softworkz at hotmail.com> wrote:
> Hi,
>
> I am looking for some guidance regarding future plans about processing
> subtitle streams in filter graphs.
>
> Please correct me where I'm wrong - this is the situation as I've understood
> it so far:
>
> - Currently, ffmpeg filter graphs do not support processing subtitle streams
> - This is why filters like 'subtitles' and 'ass' need to open, read and
> parse the media file a second time  in parallel instead of just taking the
> subtitle events from ffmpeg'demuxing
> - For graphical subtitles, there exists the so-called 'sub2video' workaround
> which is injecting the the graphical subtitle overlay images into the video
> filtergraph by declaring them as video
> - The 'sub2video' was meant to exist until filtering would support subtitle
> streams
> - A while ago, Clement Boesch submitted a patch for adding subtitle streams
> to filtergraph processing
> (https://patchwork.ffmpeg.org/project/ffmpeg/patch/20161102220934.26010-1-u@pkh.me/)
> - I read through all the discussion about it, but nothing happened
> afterwards and I couldn't find any indication about why it didn't get merged
>
>
> I'm asking because I'm intending to implement a subtitle filter that
> operates on in-stream data rather than a separate input and that will render
> text on transparent frames for later overlay.
>
> The possible options that I have identified so far for creating that kind of
> "subtitle rendering filter" would be:
>
> - Create a video source filter and implement some hack to get the subtitle
> data from the decoder to that filter - or...
> - Jump on the sub2video implementation and extend it to render overlay
> images  in case of text subtitles - or...
> - check out the situation with regards to adding subtitle filter support in
> ffmpeg and ask about plans for this
>
> That's where I stand right now. Does  it even make sense, the way I
> summarized it?`

Very nice summarization.
Main developer working on this is very busy.
Your best bet is to start from his branch and continue work on it.

>
> Thank you very much,
>
> softworkz
>
>
>
> .
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