Cannot play MP4 (H264, AAC) in web players (error s3014/s3015)

[alekdavis]

Server Version#: 1.19.3.2852
Player Version#: 4.34.2

I saw a similar issue posted in the Synology (Plex Media Server, Synology DS918+, streaming ALAC on Safari, Error code: s3014 (Media)) and Linux (Plex web app error s3014/5/6 ONLY with AAC 5.1 audio - #15 by kernelfergus) subgroups, but these were old posts with no resolution that would apply to a Windows server. In my case, it is the same issue: an MP4 plays fine in the desktop app, but not in the browsers (Chrome or Edge), which return error:

An error occurred trying to play “My media file”.
Error code: s3014 (Media)

I optimized the file (using Original Quality setting), but it would not play either (it would show error s3015). Any ideas what to do?

[alekdavis]

It looks like I was able to fix it by going into the Plex Web - Debug settings, and unchecking both the Direct Play and Direct Stream options (need to restart PMS, too). Kind of defeats the whole no-transcoding thing but at least now I can play the videos. The problem is that it’s a client-side setting, so if anyone from my circle (friends, family) has this issue, I’d need to walk them through the workaround.