[FFmpeg-user] isolate 'voices', move them, and mix into another audio stream

[Mark Filipak]

On 01/06/2025 14.26, Paul B Mahol wrote:
>> Am 01.06.25 um 17:48 schrieb Paul B Mahol:
>>> On Sun, Jun 1, 2025 at 3:40 PM Mark Filipak <markfilipak.imdb at gmail.com>
>>> wrote:
>>>> I have two ac3 audio streams. One is 'voices+noise', the other is just
>>>> 'noise' -- no voices. I want
>>>> to take 'voices+noise', remove 'noise' leaving just 'voices', then mix
>>>> 'voices' into a latter,
>>>> clipped version, call it 'sounds'. I could do it with Audacity, but I'd
>>>> like to do it with FFmpeg,
>>>> if possible.
>>>>
>>>> I seek experienced guidance because I've never done this before and I
>> want
>>>> to use the best audio
>>>> mixer 'filter' available -- knowing what's best comes only via
>> experience.
>>>>
>>>> The full story:
>>>>
>>>> "2001, A SPACE ODYSSEY" has a tedious, 2:58.136 prelude that is just
>>>> 'noise', after which the MGM
>>>> Lion appears. When I made an mp4, I cut 'm2ts 0..178.136' out leaving
>> just
>>>> 'm2ts 178.136...', which
>>>> is now 'mp4 0...', which begins with the MGM Lion.
>>>>
>>>> When I finished, I discovered that in their comments track, Keir Dullea
>>>> and Gary Lockwood introduce
>>>> themselves during that 'noise'. Their 'voices' spans 'm2ts 0..34.034'.
>>>>
>>>> I want to take 'm2ts 0..34.034', remove the 'noise' so that only
>> 'voices'
>>>> is left, then mix 'voices'
>>>> into 'mp4 0..34.034', over the MGM Lion. There's a little more clipping
>>>> and joining to be done but I
>>>> can handle that.
>>>>
>>> Need actual files.
> 
> I need exact files that Mark have.

Why, Paul? This isn't troubleshooting. It's how-to.

I need to do this:

1) 'voices' = mix('voices+noise',invert('noise')). 'voices+noise' is an existing ac3. 'noise' is 
another ac3 that is identical but without voices. 'amix' is a mixer, but is it the best mixer? More 
important: I don't know of any audio filter that will invert().

followed by this:

2) output = mix('audio','voices'). 'audio' is an existing ac3.