[Ffmpeg-devel] [PATCH] ffmpeg.c: resample when wanted

[Tomi Ollila]

Hi

A few days ago I tried to crop and rescale one 4:3 recording to 16:9
format. The original material had resolution 720x576 and I gave options
-croptop 92 -cropbotton 52 -s 720x576  to ffmpeg to do the job.

To my suprise this was no-op. No cropping and no scaling (I've been
succesful with this earlyer, but my input material must have been
704x576...)

After many iterations and so (option tuning, reordering, many ffmpeg 
recompilations) which none helped I browsed through ffmpeg.c source;
and there it was:

--8<----8<--
                } else if ((codec->width == icodec->width + 
                                (frame_padleft + frame_padright)) &&
                        (codec->height == icodec->height +
                                (frame_padtop + frame_padbottom))) {
                    ost->video_resample = 0;
                    ost->video_crop = 0;
                    ost->video_pad = 1;
--8<----8<--

Original 720x576, requested 720x576, all paddingss 0: that matched, it just
ignored the fact that I wanted to crop it and then rescale (resample)
back to the original resolution (with aspect 16:9).

--

I've created patch that fixes this. The initial thought is that 
if after cropping and padding the source the resolution won't be
the target one resampling is needed. If not, it is checked whether
padding and/or cropping is requested.

I also wrote a test script to test all these cases, which are:

1) no resampling nor cropping nor padding
2) crop
3) pad
4) crop and pad (which doesn't work (no change there)) (*)
5) resample
6) resample, crop
7) resample, pad
8) resample, crop, pad

All tests (except that 4) produced expected results (though I 
did not check whether padding were done before or after resampling...)

The (gzipped) patch (against cvs 2005/09/10) is attached at the end 
of this mail. It is also available at

http://www.iki.fi/too/ffmpeg-reqcropad.patch

The test script is available at

http://www.iki.fi/too/ffmpeg-reqcropad-test-20050910.sh


(*) test case 4 above: with my limited knowledge I don't know
    what to do with this. The unpatched code just ignored one
    or either case. Here instead of outputting junk around the
    pictures there are 3 options: 1) ignore either crop or pad,
    2) forbid giving both options (when not resamping(!?)) and
    3) fix the issue. (or 4: don't do anything and confuse users
    that do such peculiar things ;))


Anyway, I wish you see the patch good to be applied.

Tomi

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