It’s been a long time since I’ve encountered major playback issues with Plex on Chromecast, but within the last few weeks or server versions I am starting to get h4 (codec not supported) errors on my ChromeCast Ultra for most video files with FLAC audio. This occurs whether the cast is initiated from Plex Web or the Android app; meanwhile, my gen 2 ChromeCast in another room is apparently unaffected and is able to play these files just fine.
I have taken pretty reasonable notes on my issue if it would be more helpful to start a new topic, but it certainly seems like Plex still isn’t detecting all of the supported codecs or formats mentioned in the developer guidelines earlier in this thread. Is there any way we could get some confirmation that Plex is still aware this is an issue?