[FFmpeg-user] combining concat filter with closed caption extraction

[Leo Butler]

Nicolas George <george at nsup.org> writes:

> Leo Butler via ffmpeg-user (12020-06-10):
>> ffmpeg -i C.mkv -f lavfi 'movie=C.mkv[out0+subcc]' -map 0 -map 1:s D.mkv
>
> You are missing a -i in this command line.
>
>> Question: Is there a way to reduce this to one pass?
>
> With the -i, it becomes obvious: 'movie=C.mkv[out0+subcc]' is just
> another input, like B.ts.
>
> Regards,

Sorry, yes there is a syntax error in my question, but no, that is
irrelevant to my question. Let me repeat the question (with the syntax
error corrected):

  Currently, the only way I know to extract/insert closed captions as a
  subtitle stream is in 2 passes. Something like
  
  ffmpeg -i A.ts -i B.ts -filter_complex '[0:0][0:1][1:0][1:1]
  concat=n=2:v=1:a=1' C.mkv
  
  ffmpeg -i C.mkv -f lavfi -i 'movie=C.mkv[out0+subcc]' -map 0 -map 1:s D.mkv
  
  (In practice, A.ts and B.ts are segments from the same file).
  
  Question: Is there a way to reduce this to one pass?
  
  I am using a recent version of ffmpeg compiled from the git repository.

To be more explicit:

Rather than creating the file C.mkv in the first pass, can the lavfi
filter use the video output stream of the concat filter directly?

Leo