How to open .MP4 files (MPEG-4 videos) on Android, Windows and Linux

MP4 is the most common video format there is, so it’s puzzling when one refuses to play. A phone recording stuck at 0:00, a download with sound but a black screen, an .M4V from an old iTunes library: each has its own cause, and most have a fix.

For the everyday case, all you need is a player that brings its own decoders. Folders has one, built on the open-source mpv engine. It’s free and plays MP4 and M4V files on Android, Windows and Linux.

What is a .MP4 file?

MP4 is short for MPEG-4 Part 14, an international standard for a video container. A container is a box: the .mp4 extension says how the file is packed, not which codec compressed the picture. Usually that’s H.264 video with AAC audio, but newer files often use H.265 (HEVC) or AV1. An MP4 can also carry extra audio tracks, text subtitles and chapters.

The format grew out of Apple’s QuickTime format, which is why MP4 and MOV files are so alike inside. Both are made of “boxes”, including one called moov that works as the file’s index: it tells a player where every frame is.

Extension	What it is
.mp4	Standard MPEG-4 video, from phones, cameras, downloads and editing apps
.m4v	Apple’s variant of MP4, used by iTunes and some converters such as HandBrake

An M4V is built the same way as an MP4. The catch is that films and episodes bought from the iTunes Store come as M4V protected with Apple’s FairPlay DRM, and those only play in Apple’s own apps.

How to open a .MP4 file with Folders

Android

1. Install Folders from the download page and give it access to your files.
2. Find the video. Your camera’s recordings are usually in DCIM, downloads in Download, and Folders’ search finds a file by name.
3. Tap it. The video player opens and starts playing.
4. Opening from WhatsApp, Gmail or another app? Choose Open with → Folders.

The Toolbox’s Video player also lists every folder with videos, counting what you haven’t watched.

Windows and Linux

1. Install Folders and browse to the video.
2. Double-click it to play.
3. On Windows, right-click an MP4 in File Explorer and choose Open with → Folders; the installer adds it there for MP4 and M4V.

What you can do with it in Folders

• Pick up where you stopped. The player remembers your place, and the library’s round Play button resumes the last video.
• Subtitles. Use a track stored in the MP4, an .srt with the same name as the video, or one you pick. None at all? Search online… guesses the title from the file name and saves the subtitle you choose beside the video, as Movie.eng.srt for example. Delay, size and colour are adjustable.
• Audio tracks and delay, for a second language, or when lips and sound drift apart.
• Speed and a sleep timer, to slow down a tutorial or stop playback after a set time.
• Zoom. Pinch to zoom and move the picture on a phone; Ctrl and the mouse wheel on a computer.
• Picture in picture on Android, and a small always-on-top window on computers. On Android, playback controls also appear in the notification and on the lock screen.
• Decoder choice: HW, HW+ (Android only) or SW, handy when a 4K HEVC or AV1 file stutters.

Folders plays MP4s; it doesn’t cut, compress or convert them.

Other ways to open .MP4 files

• Media Player (or Films & TV) on Windows, and your phone’s gallery app on Android, play most MP4s.
• VLC: free on every system, and plays almost anything.
• A web browser: drag an MP4 into a Chrome, Edge or Firefox tab.

Problems opening a .MP4 file?

• A recording that won’t play at all. If the phone or camera died, or the app crashed, while recording, the moov index was never written. No player can open it as it is. Tools such as untrunc can often rebuild the index using a healthy video from the same device.
• Sound but no picture on Windows. The video is probably HEVC. Windows’ own players need Microsoft’s HEVC Video Extensions, a small paid add-on from the Store. Folders’ player is built on mpv, which carries its own decoders, so it doesn’t depend on that add-on.
• Choppy 4K playback on an older phone. Switch between HW and SW in the player. If it still stutters, the phone may be too slow for that file.
• An M4V that says it isn’t authorised. That’s iTunes DRM. Only Apple’s apps, signed in with the account that bought it, can play it.

Questions people ask

Why won’t my MP4 play on Android? Usually it’s an HEVC or AV1 video the built-in player can’t handle (Folders can), or a recording that was cut off, which needs a repair tool.

How do I convert M4V to MP4? A DRM-free M4V is already an MP4 inside, so renaming the extension to .mp4 often just works (Folders can rename files). For a real conversion, use HandBrake. Protected iTunes files can’t be converted.

MP4 vs MKV: what’s the difference? Both are containers. MP4 is supported almost everywhere; MKV takes more kinds of audio and subtitle tracks. See how to play MKV videos with subtitles.

Is an MP4 file safe? A real MP4 is just video. Watch out for names like movie.mp4.exe, which are programs, and for sites that say you must install a “codec” to watch something.

Also see how to open MOV files, or browse all 382 file types Folders opens.