[FFmpeg-user] How can I convert mpeg2 5.1 audio to ac3?

[Moritz Barsnick]

On Wed, Nov 05, 2014 at 14:01:37 -0500, Luke Davis wrote:
> Steve Harris has one or two LADSPA effects for working with Dolby Surround, 
> which may be what you're talking about here if I understand the most recent 
> post correctly (I have not been following the thread)
> 
> http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html#tth_sEc2.102

That's actually the exact opposite:
"It allows you to encode four channels of sound into a stereo
compatible stream that will be decoded by a Dolby1 Surround/Pro-Logic
decoder into Left, Right, Center and Surround signals."

ffmpeg already (apparently) supports this, see "-matrix_encoding",
https://www.ffmpeg.org/ffmpeg-resampler.html 

The original poster needs the opposite, a decoder: 2 channels back to
5.1 (or 4.0).

I have been at a total loss when googling. The only free software I
have found is AC3Filter, http://www.ac3filter.net/ . I actually missed
this important sound, but see it now: It's open source, and claims to
be GPL2 (plus/minus the licenses of other included code). I'm still
skimming through its code though, looking for the code which
accomplishes the up-mix.

Moritz