Am using Windows 10 v20H2 build 19042.928 and Audacity 2.4.2
Is there any way to make Audacity open THD+AC3 files directly?
(one way is to convert THD+AC3 to FLAC using eac3to, as Audacity opens FLAC files)
When Audacity is asked to save an 8-ch audio file to AC3 (which normally handles only 6-ch), it simply discards the extra 2 channels or lets you assign them manually. What is the correct way to downmix 8-ch audio to 6-ch AC3?
This sort of thing is difficult for open source software as there is a very real risk of falling foul of patent laws.
TrueHD is patented by Dolby.
Last time I looked, FFmpeg had an experimental, reverse engineered TrueHD codec. I don’t know what the current status of that codec is, and given that it may infringe on Dolby’s patents it may not be enabled in the FFmpeg library that you are using.
If you have a TrueHD encoder that works, then perhaps you could export as 8 channel WAV or 8 channel FLAC and then use your encoder to create an 8 channel TrueHD AC3.