Format overview
What is an MP4 file?
MP4 is an ISO base media container that can store video, audio, subtitles, chapters, and metadata. The container supports several codecs; H.264 video with AAC audio remains a common compatibility baseline, while HEVC and AV1 can improve compression on newer systems.
M4V is a closely related extension often associated with Apple video. Extension changes alone do not alter the streams or remove restrictions.
Compatibility
Why MP4 is widely supported
Browsers, phones, tablets, televisions, media servers, and editing applications commonly recognize MP4. Compatibility still depends on the video profile, level, bit depth, audio codec, frame rate, and resolution.
An HEVC MP4 may fail on a device that plays H.264 MP4, and multichannel or lossless audio can be less portable than AAC. Check the complete media specification when troubleshooting.
Practical use
When should you convert to MP4?
Choose MP4 when the destination needs a compact, broadly playable file. H.264 is suitable for the widest range of devices; HEVC can reduce bitrate for newer hardware. Preserve the source resolution and frame rate unless the destination requires another value.
Do not use MP4 when you must retain Blu-ray Dolby TrueHD tracks or many subtitle and audio streams. Multi-track MKV is better suited to that archive workflow.