MP4 is a media container format that can hold video, audio and other timed information. It supports a range of encodings and arrangements, including forms used in streaming workflows. The extension alone therefore says little about the exact codec, resolution or audio tracks that a device will need to decode during playback.
A practical example
A phone and a television may both recognise an MP4 file, yet only the phone plays all its tracks. Their container support overlaps, but differences in the video or audio decoder can still explain the television's incomplete playback result.
A common misunderstanding
Do not equate MP4 with one video codec or with a downloaded film. It is a packaging format, and its contents and use can differ substantially between sources.
Related terms
Further reading
Stable technical definition. Editorial approach