While trying to use pan to subtract two channels (actually to see whether a two-channel file I have is effectively mono), I noticed that "pan=mono|c0=-0.5*c0+0.5*c1" would work, while "pan=mono|c0=0.5*c0-0.5*c1" would cause the parser to choke, expecting a '+'.
Using this (second) patch, you could now not only "check" for channel differences, but also eliminate centered stereo signals, like an "out of phase stereo" ("karaoke") filter. Meanwhile I also noticed that "pan=mono|c0<-0.49*c0+0.51*c1" would be incorrectly amplified by a factor of 50 (= 1/(-0.49+0.51)), which can lead to clipping with any non-related inputs, as the negative gain factor actually only inverts the input's phase, not its level. This is fixed in the first patch. Moritz Barsnick (2): lavfi/pan: renormalize negative gain coefficients properly lavfi/pan: allow negative gain parameters also for other inputs than the first named doc/filters.texi | 2 +- libavfilter/af_pan.c | 10 ++++++---- 2 files changed, 7 insertions(+), 5 deletions(-) -- 2.7.4 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel