From PR #1:
Downmixing is limited to standard stereo. It is unclear whether the downmixing is done correctly -- the liba52 and VLC appear to downmix to stereo a bit differently. It sounds reasonable, albeit a little quiet.
The decoder seems to decode several 5.1 test streams. However, it does not properly handle 2.0 or 2.1 streams correctly (e.g., http://samples.mplayerhq.hu/A-codecs/AC3/monsters_inc_2.0_192.ac3, http://samples.mplayerhq.hu/A-codecs/AC3/TomorrowNeverDies-2.1-48khz-192kbit.ac3, and http://samples.mplayerhq.hu/A-codecs/AC3/a52dec-streams/thx_2_0).
From PR #1: