7.1 downmix function?

[tormento]

Originally Posted by tebasuna51

Of course there are downmix functions and also upmix functions.

Did you ever try to understand how good is DEE downmix function?

[tebasuna51]

DEE ddp Downmix

7.1 -> 5.1 Something like:

FL' = 0.54*FL
FR' = 0.57*FR
FC' = 0.64*FC
LF' = 1.00*LF
SL' = 0.4*SL + 0.4*BL
SR' = 0.4*SR + 0.4*BR

7.1 -> 2.0 Something like:

FL' = 0.54*FL + 0.45*FC + 0.34*SL + 0.33*BL [1.66 clip risk]
FR' = 0.48*FR + 0.45*FC + 0.30*SR + 0.34*BR [1.57 clip risk]

5.1 -> 2.0 Something like:

FL' = 0.54*FL + 0.38*FC + 0.47*SL [1.39 clip risk]
FR' = 0.48*FR + 0.38*FC + 0.46*SR [1.32 clip risk]

[pandy]

This triggered my curiosity - isn't feasible to use SOFA filter https://ffmpeg.org/ffmpeg-filters.html#sofalizer to downmix 7.1 (up to 9 channels) to 2 channel? Of course some synthetic SOFA file can be used if HRTF is unwanted.

[richardpl]

Can use headphone filter, and also afir filter in casea impulse response files are really big.

[tebasuna51]

Originally Posted by tebasuna51

1) If your input is 7.1, first do a 7.1 -> 5.1 downmix with the compand selected (see precedent posts):
-filter_complex "asplit [f][s]; [f] pan=3.1|c0=c0|c1=c1|c2=c2|c3=c3 [r]; [s] pan=stereo|c0=0.5*c4+0.5*c6|c1=0.5*c5+0.5*c7, compand=attacks=0:decays=0:points=-90/-84|-8/-2|-6/-1|-0/-0.1, aformat=channel_layouts=stereo [d]; [r][d] amerge [a]" -map "[a]"

WARNING: when use these filters with a recent ffmpeg v5.1 there are a regression detected.

Use a ffmpeg v4.4 until the regression was solved.

[tebasuna51]

The regression detected is not fixed.

I open a new one

[Selur]

Originally Posted by tebasuna51

The regression detected is not fixed.

Confused, according to your link:

Status: new → closed

Fixed in 93a9ee7afd7bf2e019490117f1bada30724a0200

[tebasuna51]

It is not fixed, now do other remix unwanted, see the image in the new one.

[Balling]

Originally Posted by tebasuna51

It is not fixed, now do other remix unwanted, see the image in the new one.

Fixed now.

[tebasuna51]

I test the Latest Auto-Build (2023-02-20 12:35) in https://github.com/BtbN/FFmpeg-Builds/releases
Seems work correctly now:

1) 7.1 -> 5.1 downmix with the compand selected (see precedent posts):
-filter_complex "asplit [f][s]; [f] pan=3.1|c0=c0|c1=c1|c2=c2|c3=c3 [r]; [s] pan=stereo|c0=0.5*c4+0.5*c6|c1=0.5*c5+0.5*c7, compand=attacks=0:decays=0:points=-90/-84|-8/-2|-6/-1|-0/-0.1, aformat=channel_layouts=stereo [d]; [r][d] amerge [a]" -map "[a]"

There are two 'green messages':
[Parsed_pan_1 @ 000001fc795c1d80] Pure channel mapping detected: 0 1 2 3
It always appears no matter what I use:
pan=3.1|c0=c0|c1=c1|c2=c2|c3=c3
until
pan=FL+FR+FC+LFE|FL=FL|FR=FR|FC=FC|LFE=LFE

And
[Parsed_amerge_5 @ 000002ac9b81ce00] Input channel layouts overlap: output layout will be determined by the number of distinct input channels
But any attempt to specify the correct channel layout for the surround channels, instead 'stereo', like:
pan=SL+SR...,compand...
or
aformat=channel_layouts=SL+SR
abort the process.

2) I suggest use for 6.1 -> 5.1 downmix:

-filter_complex "asplit [f][s]; [f] pan=3.1|c0=c0|c1=c1|c2=c2|c3=c3 [r]; [s] pan=stereo|c0=0.412*c4+0.588*c5|c1=0.412*c4+0.588*c6, compand=attacks=0:decays=0:points=-90/-85.4|-8/-3.4|-5/-1|-0/-0.1, aformat=channel_layouts=stereo [d]; [r][d] amerge [z]" -map "[z]"

[Balling]

What do you suggest should happen with Back Centre channel? We do not support mixing that into back channels.
https://trac.ffmpeg.org/ticket/10207#comment:4

[tebasuna51]

Originally Posted by Balling

What do you suggest should happen with Back Centre channel? We do not support mixing that into back channels

Your sample is a problematic AAC 6.0 (MediaInfo and faad inform with channel layout L R C Cb Lb Rb).

qaac can't decode it: ERROR: Not available input file format

NeroAacDec decode it in wrong (I suposse) channel order (maybe FL FC FR SL BC SR) without channel mask.

faad seems decode it without channel mask with the order FL FR FC BC SL SR

ffmpeg decode it like 5.1 but with channel mask 0 in the same order than faad.

To convert that 6.0 to 5.1 I suggest try:

-filter_complex "asplit [f][s]; [f] pan=3.1|c0=c0|c1=c1|c2=c2|c3=0.0*c3 [r]; [s] pan=stereo|c0=0.412*c3+0.588*c4|c1=0.412*c3+0.588*c5, compand=attacks=0:decays=0:points=-90/-85.4|-8/-3.4|-5/-1|-0/-0.1, aformat=channel_layouts=stereo [d]; [r][d] amerge [z]" -map "[z]"

[Balling]

channel layout L R C Cb Lb Rb, yep, where Cb is back center. Wav does support that channel. https://learn.microsoft.com/en-us/wi...rmatextensible

So your command puts back center where?

[tebasuna51]

Half mixed in surround channels, make a fantom back center.