I have 2 Chromecast v2 at home and both are having the same issue. When trying to cast some mp4 files, the Chromecast will not play them. It will load them, display the seek bar but the whole TV stays black. Looking at PMS when casting, it shows that my Chromecast is "Direct Play" and there's no transcoding involved. I've looked at my files that are not working, and they are H264/AAC according to Plex. That should be supported in the Chromecast according to Google specs. If I play the movie on my Android phone, the PMS is transcoding the stream to my phone.
The weird this is that I have few others mp4 files that are also H264/AAC and they are working fine on both Chromecast. I am not knowledgable enough in codecs to tell you if there are other differences between the files/codecs. I just see H264/AAC in Plex on the movie details. I'm happy to look further if you have some tools for me to investigate further.
I thought that I could work around this issue by forcing transcoding to the Chromecast but that didn't work. I tried forcing using Audio Boost, Subtitles or a different Video Quality, but whatever I do the stream is still "Direct Play" to my Chromecast.
I'm running the latest version of PMS (22.214.171.12466) on Ubuntu Server (minimal setup; no GUI). My Ubuntu Server is running inside an ESXi 6.5 host. All my files are hosted on a Synology NAS.
I've been using Plex for years and been a Plex Pass member, but it is the first time that I have to troubleshoot an issue, so I don't know where to look really. If at the very least it would transcode I wouldn't see the issue, but the Chromecast v2 should be able to handle direct play of H264/AAC as far as I know.
Thanks for your help,