I posted the question on the Plex forum :
https://forums.plex.tv/discussion/17...pms-guidelines
But from what I know, Plex is serving the files as-is. The only transcoding that is happening is with regard to the requested bandwidth, compatible 2D video and audio output, depending on the client that is requesting the streaming.
I know by fact that when I play a 3D movie, I have to change the playback mode from transcode to DirectPlay, otherwise it won't work.
I will try to convert a SBS file to FS, see if I can pull this off
.