[FFmpeg-trac] #2520(avfilter:new): Alpha channel does not work on GEQ filter on RGB mode

[FFmpeg]

#2520: Alpha channel does not work on GEQ filter on RGB mode
----------------------------------+--------------------------------------
             Reporter:  jbvsmo    |                     Type:  defect
               Status:  new       |                 Priority:  normal
            Component:  avfilter  |                  Version:  git-master
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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 Summary of the bug:
 The "alpha_expr" option of GEQ filter does not write in the alpha plane on
 RGB mode. I'm not sure if the "alpha_expr" was intended to be used in RGB
 mode, but it would be handy.

 Simple input
 {{{
 ffmpeg -i file.mp4 -vf "geq=r=p(X\,Y):alpha_expr=10" out.mp4
 }}}
 Overlayed:
 {{{
 ffmpeg -i file.mp4 -vf "geq=r=p(X\,Y):alpha_expr=10[a];
 movie=file2.mp4[b]; [b][a]overlay" out.mp4
 }}}

 There's no change in the alpha channel (I'm using the overlay filter on
 another video). if you replace "r" by "lum_expr" (using YCbCr mode instead
 of RGB), the output can be overlayed with transparency.

 Reading the code, the inputs "r", "g" and "b" cannot be used with any of
 "lum_expr", "cb_expr" and "cr_expr", but there's no checking for the usage
 of "alpha_expr" them.

 I tried forcing many input formats, including "rgba" and "yuva444p".


 Version:
 {{{
 $ ffmpeg -version
 ffmpeg version N-41713-g53efb2f
 built on Apr 30 2013 16:23:43 with gcc 4.7 (Ubuntu/Linaro 4.7.2-2ubuntu1)
 configuration: --enable-gpl --enable-libass --enable-libfaac --enable-
 libfdk-aac --enable-libmp3lame --enable-libopencore-amrnb --enable-
 libopencore-amrwb --enable-libspeex --enable-librtmp --enable-libtheora
 --enable-libvorbis --enable-libvpx --enable-x11grab --enable-libx264
 --enable-nonfree --enable-version3 --enable-libfreetype --enable-
 libvidstab
 libavutil      52. 27.101 / 52. 27.101
 libavcodec     55.  6.100 / 55.  6.100
 libavformat    55.  3.100 / 55.  3.100
 libavdevice    55.  0.100 / 55.  0.100
 libavfilter     3. 61.101 /  3. 61.101
 libswscale      2.  2.100 /  2.  2.100
 libswresample   0. 17.102 /  0. 17.102
 libpostproc    52.  3.100 / 52.  3.100
 }}}

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2520>
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