As title, Wish update!
Why?
MPV is not used in the iOS Plex client.
MPV is not used in the Plex Web app.
MPV is usually updated if it’s technically feasible in both “Plex HTPC” and “Plex for Windows/Mac/Linux”.
First of all, I understand you are confused . Now, I have some problems playing some videos on plex PC and ios Plex, but it is good on Android. I think it is because the PC and ios use mpv, while Android uses exoplayer v2. Then I test the latest version of mpv on my PC, and find that the video play normally, so I like to let plex update mpv
Here is the scrrenshot which capture in IOS plex:
And here is the test video:
https://drive.google.com/file/d/191nfyduymD3n1h6lMEQoOwNNXtpQ3a8r


