Hi folks, really glad to see the Plex app on Sonos as it solves my two biggest gripes with the Sonos library support - 1) Sort Order tag support and 2) allowing multiple libraries (to sub-divide big collections).
I've got Plex server running on a Synology DS115, which works great from the Sonos library. But from the Plex app for Sonos, it's unable to keep a stream running. Some digging and I figured out that the app must be transcoding (which the little NAS CPU can't keep up with). My files are mostly in Apple Lossless (ALAC) or FLAC, with some in high-bitrate MP3.
The MP3 files play without issue, and with some testing the FLAC files seem to work. ALAC doesn't. All of the above are natively supported by Sonos, so no transcoding is needed - but it appears the app is doing it. I can't tell if FLAC files are being transcoded (since they seem to work and there's no status I can find that says if it's playing MP3 or FLAC).
Can someone confirm that the Sonos Plex app is playing FLAC files without transcoding? As long as that's done natively, I'll convert my ALAC files to FLAC - no problem!