Feature Request: add support to EAC3 7.1

[ackbc]

since EAC3 is much more advanced than normal AC3 which can only do 6 channels (even Amazon online streams are all using eac3), and many films that already carry 7.1 audiotracks, if ffmpeg could support eac3 7.1 (input output) or general 7.1 that would be great, the vote for eac3 is that it can keep most (objectively) of the sound quality with lower bitrates. The only software that supports eac3 7.1 is some obsolete software only runs on Mac.. thanks a lot.

attach three samples for testing, all three are 7.1 files, the third one is in EAC3, thanks

[Balling]

Duplicate decoding is supported: #4608 and encoder -- no support #3595, patches welcome