Many professionals playblast to a high-quality .avi or .webm format and then use Clipchamp or Handbrake to convert it to a standard H.264 MP4 for sharing.
If your video won't load, it is likely a missing system-level codec rather than a Maya bug. Maya.mp4
If you need to import an MP4 into Maya to use as a background for tracing movements: Many professionals playblast to a high-quality
Before working with heavy video files, ensure Autosave is enabled under Windows > Settings/Preferences > Preferences > Files/Projects to prevent data loss if a codec causes a crash. MP4 files use temporal compression, which makes "scrubbing"
MP4 files use temporal compression, which makes "scrubbing" (dragging) through the timeline laggy or inaccurate as Maya tries to calculate compressed frames.
By default, Maya often only supports .avi (Windows) or .mov (Mac) for playblasts. How to Get an MP4:
Use a tool like FFmpeg or Shutter Encoder to export your MP4 as a series of images.