[Ffmpeg-devel] interlace, duration and vhooks

Måns Rullgård mru
Tue Jul 26 15:09:21 CEST 2005

Marcus Engene said:
> Running
>  ffmpeg -v 2 -i file1
> I get one duration of a file but if I convert the file to
> another format
>  ffmpeg -v 2 -i file2
> the duration seems not always to be correct?
> I had one thing in mind to get around this; I convert files
> to another format and what if I use a vhook that just counts
> the frames and on exit writes # of frames to a file? Eg:
>  ffmpeg -i infile -vhook '/.../counthook.so -f /.../apa.txt' outfile
> If this is alright, I will get a problem with interlace vs progressive.
> The fps output says the number of frames, not fields, and as it looks
> now, vhooks cannot say if they're processing a full frame or an
> interlaced frame (field?)?

The decoders always return complete frames.  For interlaced content, each
frame has the top and bottom fields interlaced.  At least for frame
coded pictures this is true.  I don't think I've ever come across any
field coded material, so I'm not certain how that is dealt with.

> Would it be a lot of work to add in the probe output from ffmpeg that
> a file is interlaced?

There is no reliable way to determine whether a file is interlaced, so it
is more or less impossible.

M?ns Rullg?rd
mru at inprovide.com

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