I have saved MP3s stored in my vault - the actual files are the correct size. I have created a link in a page - the Obsidian player does load - but the total time for the video shows 0:00/0:00. If I go to the actual file, I can right-click and play via iOS Music (using Mac OS desktop). So the file does exist and is not corrupted.
Most likely this is related to the encoding used within the MP3 file. MP3 files can contain various encoding for the music/video they’re holding, and not all are supported in all players (an Obsidian is a player in this regard).
So you need to change the encoding to something Obsidian accepts.