i konw .mpg isn’t supported, but the doc also said
You can now enable and allow non-standard codecs for WMF Media from the Plugins section of Project Settings.
https://docs.unrealengine.com/latest/images/Engine/MediaFramework/TechReference/ProjectSettings.jpg
By default, the player plugin will attempt to detect audio and video codecs that are not supported by the operating system, requiring the user to install additional codec packs.
and i found some logs:
LogWmfMedia:Verbose: Set rate from 0.000000 to 1.000000
LogWmfMedia:Verbose: Starting playback at beginning
LogWmfMedia:Verbose: Media session event: Session Rate Changed: The request is invalid in the current state.
LogWmfMedia:Verbose: Media session event: Session Started: The request is invalid in the current state.
LogMediaAssets:Verbose: MediaSoundWave resuming sink.