Quote:
Originally Posted by qyot27
I don't know if/how well FFmpeg can handle LFE mixing. Most of the time when I process my (4K or not) Blu-ray rips for watching on my desktop, I use eac3to to downmix and mix the LFE channel into the stereo signal (then encode the result to Opus and remux with the original video stream) so that when watching it back with mpv it doesn't cause nasty clipping when I try to use any volume boosting.
Of course, if you've got the right speaker setup, this is probably a completely moot point, but it is something to consider if not.
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Usually LFE is ignored during downmixing (Dolby recommendation - personally i think this is due high risk of over-ranging but sane amount of LFE should be fine). Personally i use private down-mix:
for more than 5.1 to 5.1 scheme (critical feedback appreciated - didn't found anything on this topic - also Dolby documentation not very helpful)
Quote:
"pan=5.1(side)|FL<1.414FL+FLC|FR<1.414FR+FRC|FC<2.828FC+FLC+FRC|LFE=LFE|SL<SL+BL|SR<SR+BR,aresample=resampler=soxr sr=48000:cutoff=0.990:dither_method=0"
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or quite classic 5.1 (compatible with 5.1 side and rear) to 2.0 downmixing (additional dynamic normalizer and resampler to 48k active)
Quote:
"pan=stereo|FL < FL+1.414FC+0.5BL+0.5SL+0.25LFE|FR < FR+1.414FC+0.5BR+0.5SR+0.25LFE,dynaudnorm=p=1/sqrt(2):m=100:s=20,aresample=resampler=soxrsr=48000:cutoff=0.990 recision=20"
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or quite interesting HRTF based downmixed (main intention is headphone listening for example on your portable audio device
7.1 to 2.0@HRTF:
Quote:
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"[0:a:0]aformat=channel_layouts=7.1,aresample=resampler=soxrsr=48000:cutoff=0.990:dither_method=0,asplit[71][sofai];[sofai]sofalizer=sofa=dodeca_and_7channel_3DSL_HRTF.sofa:gain=11:lfegain=9[sofao]"
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File 'dodeca_and_7channel_3DSL_HRTF.sofa' is a HRTF coefficient set available for example in VLC distribution