Substitute center channel in ac3 5.1 file

[lenberg]

Hi all!
Is it possible to substitute the center channel of a ac3 5.1 file, using another ac3 file that contains (only) the center channel that I want?
All the ac3 files have the same parameters, sample rate... The process should be lossless.

Thank you in advance for all the help

[sneaker]

I think it's not possible because AC3 channels use channel coupling and a shared bit pool. (Unless both encodes don't make any use of it? So basically only if a very bad/basic encoder was used.)

You can get basically lossless if you use a lossless output codec like FLAC.
https://trac.ffmpeg.org/wiki/AudioChannelManipulation

[lenberg]

Thank you. Bummer!
So what would you recommend to achieve minimal loss of quality?

Those 2 ac3 files come from a conversion from original DTS audio.

So far what I wanted to do was:
DTS file 1-> AC3 file 1
DTS file 2-> AC3 file 2
And then "merge" the channel from AC3 file 1 in AC3 file 2

But if there's another way to do it I am all ears! The resulting file HAS TO BE AC3.
Maybe converting DTS to PCM or WAV during the first conversion (where I apply some changes with ffmpeg) and then importing all the channels in Audacity, remove the channels I don't want, apply a filter on 1 of the channels and export to AC3.

[pandy]

Lossless probably not... ffmpeg may do this as already pointed by sneaker https://forum.videohelp.com/threads/390478-Substitute-center-channel-in-ac3-5-1-file#post2530998 - you need to be sure that both sources has same duration - if not then all things become more complex and way more lossy than regular channel manipulation.

[lenberg]

Yes, they have the same duration
Thank you