Video to MP4

A video file is a box holding a picture track and one or more sound tracks. MKV, MOV, WebM and MP4 are different boxes, and they can hold the same tracks. So this tool lifts each track out of your file and puts it into an MP4 unchanged, byte for byte. Nothing is decoded or compressed again, so the MP4 looks and sounds exactly like the original and is about the same size.

That also makes it fast: the work is reading the file once and writing it once. A 655 MB, 4-minute 1080p MKV becomes an MP4 in about 2 seconds on a recent laptop.

Videos whose picture is H.264, HEVC, AV1 or VP9 and whose sound is AAC, MP3, Opus, FLAC or Dolby Digital. That covers iPhone and Mac videos (MOV) and screen and game recordings from OBS (MKV), as well as MKV films in the usual formats. Videos that are already MP4s, as most Android phones save them, have nothing to convert.

WebM files can be added too, and are copied the same way, but a WebM’s VP9 picture and Opus sound play in fewer places once they are in an MP4, so this page doesn’t promise them. WebM from older browsers uses VP8 video, which an MP4 can’t carry as it is.

Each video says what it holds as soon as you add it, before you press anything. A few can’t be copied into an MP4 as they are: VP8 video from older WebM files, ProRes from editing apps, and DTS or uncompressed sound. Those say so in their row and are left alone, because changing the picture or sound itself is a bigger job this tool doesn’t do yet.

Some combinations play in fewer places: VP9 or Opus in an MP4 plays in browsers and VLC but may not in QuickTime, and HEVC may need Microsoft’s HEVC extension on Windows. The tool tells you when a video is one of them.

Every picture and sound track the MP4 can carry comes along, a film’s second language and an OBS recording’s separate microphone track included. A phone video filmed upright stays upright.

Subtitle tracks, timecode tracks and the camera data some phones record beside the video stay behind, as this tool can’t carry them into an MP4 yet. A video that has any lists them before you press Convert.

Your video is read a piece at a time and the MP4 is written to your browser’s private storage as it goes, so a long video doesn’t have to fit in memory. Chromium-based browsers such as Chrome and Edge use about 300 MB more memory while it runs, and a file twice the size needs no more. Firefox uses more, up to about 1.5 GB. We haven’t measured phones, so a very long video may be too much for one.

Your video never leaves your device: there is no server that could see it. The browser keeps the MP4 in its private storage only until you remove it; one left behind when you close the tab is cleared the next time you convert a video here.