If your default player won't open the file, it may be due to missing "codecs" (the technology that compresses the video).
: Often called the "Swiss Army Knife" of video players, it can play almost any .mp4 regardless of its internal compression. [@X_Gram_Official].mp4
: This usually means you have the audio codec but are missing the video codec (like H.264 or H.265). Switching to VLC typically fixes this. If your default player won't open the file,
: Simply double-click the file to open it in QuickTime Player or use the spacebar for a "Quick Look" preview. Switching to VLC typically fixes this
The .mp4 format is a "container" that holds video, audio, and subtitles. It is one of the most compatible formats in the world.
: If the video freezes or cuts off, the file may have downloaded incorrectly. Try downloading it again from the source. How to Create and Open an MP4 File