I have a Sony KDL-55NX810 TV that is connected to a Pioneer VSX-1122-K (a fairly capable AVR) and then through the network to a Mezzmo media server. The TV is connected to the receiver with an HDMI cable for video (ARC turned off) and an optical cable for audio.

I ripped a DVD to an ISO and then encoded it to a MP4 with AC3 audio using HandBrake.

When I play the MP4 through Mezzmo, the receiver only says it is processing stereo sound (on its display). When I play a burned DVD from the ISO (on an old DVD player that is HDMI-ed to the receiver), it plays with surround sound, as expected.

I did nothing special for the Mezzmo installation.

I have experienced this same issue with a Plex media server and the audio coming through HDMI ARC and the TV optical output (trying to isolate if it's the HDMI out from the TV or something else).

Any ideas on how to get surround sound out of this setup for Mezzmo-served media?

Many thanks.