[FFmpeg-devel] [RFC] Google Summer of Code 2013

Reimar Döffinger Reimar.Doeffinger at gmx.de
Thu Mar 7 10:23:43 CET 2013

Kieran Kunhya <kierank at ob-encoder.com> wrote:

>> A big task that might be too difficult is full support for closed
>captioning e.g. from ATSC broadcasts.
>> Problems include: data is stored inside video frames (need a way to
>extract it) and it needs to be reordered in the same way as the video
>frames itself.
>> Also the CC stuff has quite a few advanced features, so a decoder is
>non-trivial (writing a decoder for the CC streams from WTV allows
>skipping the how to extract/reorder issues sinc that's already done for
>that format).
>> Teletext is another feature we do not yet support, and should be a
>bit simpler.
>If this side of the fence ends up merging the AVBuffer stuff, CC
>reordering should be easy since it'll just come out attached to every
>frame (though there would need to be code somewhere to merge CCs from
>two fields or two sets would need exporting).
>How you'd decode it in FFmpeg using the current API, I don't know.

So in other words it's completely useless because it won't actually work?
Splitting it at the decoder sure is a possibility of you can't be bothered to come up with a proper solution that actually is convenient and fits into the API.
Of course it means only programs that add special code for our will support it.
And WTV will end up giving you the same subtitle stream twice.

>Teletext is a lot of work; one might be able to get just the subtitles
>part working I guess.

Uh, what part of it is a lot of work?
The format is not that complex, less than ATSC captions.
Selecting a page could be done as a decoder option at first.
Supporting analog teletext could also be separate.

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