[FFmpeg-devel] libavfilter scale problem

[Vitor Sessak]

slippyr4 wrote:
> Hi All,
> 
> I'm having an issue with libavfilter, in particular the scale filter, when
> used in a chain with other filters.
> 
> I have built the latest ffmpeg+libavfilter as of today (libavfilter r5620,
> which uses ffmpeg r21854 and libswscale r30520), and built ffmpeg with
> --enable-memalign-hack --enable-shared --disable-static --enable-gpl
> --enable-avfilter --enable-libmp3lame
> 
> Firstly, I have created a 1920x1080 resolution test source with the
> following:-
> ffmpeg -r 5 -s hd1080 -i %03d.jpg 1920x1080.mp4
> 
> I want to create a chain of filters which will have the effect of rotating
> anticlockwise by 90 degrees and then scaling so that the video is sized
> 810x1920.
> 
> However,
> *ffmpeg -i 1920x1080.mp4 -vfilters "transpose,scale=810:1920"
> transposescale.mp4*
> produces an output in which the top half of the frame is correct, but the
> bottom half is solid green.
> 
> However, if i do the equivalent transformation in two stages:-
> *ffmpeg -i 1920x1080.mp4 -vfilters "transpose" transpose.mp4
> ffmpeg -i  transpose.mp4 -vfilters "scale=810x1920" transpose_then_scale.mp4
> *then the output is correct.
> 
> Is there some intricacy of the scale filter that i've not taken account of,
> or is this a bug?

It is a bug. Can you check if my latest commit to libavfilter repo fixed it?

-Vitor