MP4Box - GPAC 26.08

MP4Box is the free command-line tool for building, splitting, joining and repackaging MP4 files without re-encoding them.

It comes as part of GPAC, an open-source multimedia framework developed at Telecom Paris, and runs on Windows, macOS, Linux and Android.

There is no window to click around in, so expect to type a command or two - the useful ones are listed further down this page.

What MP4Box Actually Does - in Plain Terms

An MP4 file is a box that holds separate tracks: video, one or more audio tracks, subtitles and chapter markers. MP4Box opens that box and rearranges what is inside it, without touching the picture or sound themselves.

That is why it is fast and why there is no quality loss. A job that takes an encoder an hour, such as adding a subtitle track or swapping an audio language, takes MP4Box a few seconds.

• Mux and demux. Combine separate video, audio and subtitle files into one MP4, or pull a single track back out of one.
• Split and join. Cut a file into parts by size or duration, or stitch several parts back together.
• Fix files for the web. Interleave a file and move its index to the front, so it starts playing in a browser before it has fully downloaded.
• Prepare streaming. Package files for DASH and HLS adaptive streaming, the format video sites use to switch quality on the fly.
• Encrypt and tag. Add Common Encryption for protected streaming, and write metadata such as titles and language codes.
• Package images. Build HEIF and AVIF image files, the same family as the HEIC photos an iPhone takes.

It reads MP4, MOV, 3GP and raw streams such as H.264, H.265, AV1, AAC and AC3, plus SRT and other subtitle formats. On Windows, HEIC files it creates need HEIF Image Extensions to open in Photos.

The Commands Most People Need

Open a Command Prompt or terminal in the folder with your files and type one of these. Replace the file names with your own.

Track numbers come from the -info output, so run that first. Commands without -new change the original file, so keep a copy until you are happy with the result.

For every option, the official MP4Box documentation is kept up to date by the GPAC team.

Which Download You Need

The MP4Box download page carries the full GPAC installer for each platform. On Windows, take the 64-bit installer unless you are on a 32-bit system; it installs MP4Box along with the rest of GPAC.

The installers are GPAC's automated builds of its latest code, which the developers test on every build and describe as safe for most users. There is also a portable 7z of MP4Box on its own, for when you do not want to install anything.

Two community front-ends, Mp4-Mux-Tool and My MP4Box GUI, are on the same page for people who would rather click than type. Both are old and no longer updated, so they cover the basic muxing jobs but not the newer options.

Who Should Look Elsewhere

The tell is whether you want the file smaller or in a different format. MP4Box never re-encodes, so it cannot shrink a video, change its resolution or convert it to another codec.

Tools That Pair Well With It

MediaInfo shows the codec, bitrate and language of every track before you start, which saves guesswork about what to add or remove.

Subtitle Edit fixes timing and converts subtitle formats before you mux them in. Once a file is built, VLC Media Player is the quickest way to check every track plays.

If Windows' own apps refuse to play an H.265 file you have packaged, the HEVC Video Extension adds the missing decoder. The Video Encoders category has the rest of the encoding side.

Quick questions

Download MP4Box - GPAC 26.07 and see how it handles your files, or tell us how you got on if you have used it before.