#2520: Alpha channel does not work on GEQ filter on RGB mode
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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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