I also have this problem (or a similar one).
EDIT: I think I’m describing this other bug report: Chromecast No Longer Supports H264 Direct Play
Cast to device, Plex logo appears on screen
Select media to play, and it looks like it’s going to play for a split second, then goes back to the Plex logo.
If I select a TV series, it will rapidly “flip” through each episode before going back to the Plex logo.
If I look at the media server log, I see these kinda things for every item that it is attempting to play:
DEBUG - [Req#1c9f03/Transcode] Streaming Resource: Reached Decision id=26905 codes=(General=2000,Neither direct play nor conversion is available. Direct Play=3000,App cannot direct play this item. Direct play is disabled. Transcode=4002,Not enough CPU for conversion of this item.)
DEBUG - [Req#126/Transcode] Streaming Resource: Reached Decision id=12591 codes=(General=2000,Neither direct play nor conversion is available. Direct Play=3000,App cannot direct play this item. No direct play video profile exists for protocol http, with container mp4, and video codec h264. Transcode=4002,Not enough CPU for conversion of this item.)
I would expect the “not enough CPU” message for items that it needs to transcode (as Plex is running on a Raspberry Pi4), but I get the same message for media that I have successfully Chromecasted from that server many many times in the past.
