[MPlayer-dev-eng] Error in docs? (Preserving aspect ratio)
diego at biurrun.de
Sun May 4 23:19:11 CEST 2003
Jason Tackaberry writes:
> http://mplayerhq.hu/DOCS/encoding.html rightly suggests to crop out
> black bars in the original movie source when encoding. It then goes on
> to suggest that you should preserve the aspect ratio if you use
> libavcodec. Both excellent practices, which I follow.
> But as I was reading these docs, I noticed a problem in the proposed
> command line:
> $ mencoder sample-svcd.mpg -ovc lavc -lavcopts vcodec=mpeg4:aspect=16.0/9.0 -vop crop=714:548:0:14 -oac copy -o output.avi
> Now either there is a problem here, or I am misunderstanding something
> and as a result have messed up all my encodings. :)
> The problem, as I understand things, is that if you specify a crop
> region, you must also adjust the aspect ratio for the new size. The
> cropped region above is no longer 16/9.
> For a 16/9 DVD, the video source is usually 720x480 which gets scaled to
> 854x480. So the correct aspect ratio for the above cropped video, where
> the original is 16/9, is 714*(854/720)/548, or 1.545. The libavcodec
> option should then be aspect=1.545.
> Although I think I have a handle on this, and I think the docs are
> wrong, please do let me know if I'm misguided. :)
OK, I corrected the docs in 0_90, the web site should get updated in a
For main we should use the new autoaspect option implemented by Rich.
The correct command line should be
$ mencoder sample-svcd.mpg -ovc lavc -lavcopts vcodec=mpeg4:autoaspect
-vf crop=714:548:0:14 -oac copy -o output.avi
Rich, could you please document autoaspect in the man page?
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