The default file extension for MP4 is '.mp4'. Since the format and contents of the file varies, so does the file extensions:
MP4 doesn’t have a specific file extension. Over the years, MP4 has gained popularity due to its efficiency when compressed and portability when shared and streamed online. This makes MP4 a much more versatile file format as opposed to something like MP3. It can carry video, audio, subtitle, and other metadata within a single file. MP4 stands for MPEG-4 which comes from Apple’s QuickTime MOV format and can store more than audio. MP4 is essentially a container format that stores the data of a file, instead of the code.
