How to change a video's format for free: MOV, MKV and WebM to MP4

A video format is a wrapper, not the video itself

When you ask how to change a video file's format, the extension at the end of the name, .mp4, .mov, .webm or .mkv, is the container. It is a wrapper that holds the picture, the sound and a little timing information. The picture inside is compressed with a codec such as H.264, H.265, VP9 or AV1, and the sound with a codec such as AAC or Opus.

That difference explains why some conversions take two seconds and others take minutes. If the new container can hold the streams already in your file, the converter can move them across unchanged. If it cannot, the streams must be re-encoded, which takes real processing time and loses a small amount of detail.

The video converter is built around this idea. It shows you, before you press the button, which streams will be copied and which will be re-encoded, so you know what to expect.

What the converter opens and saves

It opens MP4, MOV, M4V, WebM, MKV and MPEG-TS files, including H.265 phone videos. It saves:

• MP4, the safe default. Phones, TVs, browsers, social networks and editing apps accept H.264 MP4.
• WebM, built for websites. VP9 video with Opus audio makes small files for HTML5 players, but Apple editing apps will not import it.
• MOV, Apple's container, preferred by Final Cut Pro, iMovie and QuickTime.
• MKV, a flexible container that accepts almost any codec. Good for archiving, though many phones and editors cannot open it.
• MP3, WAV or M4A, if you only want the soundtrack.

When it has to re-encode, it uses H.264 and AAC for MP4, MOV and MKV, and VP9 and Opus for WebM. For other audio formats or a choice of bitrates, use Extract Audio or the audio converter. The steps are in extracting audio from a video.

Convert a video to MP4 in four steps

1. Open the converter and choose your file, or drop it on the page. You will see its format, codecs, resolution and frame rate.
2. Pick MP4 as the new format.
3. Choose the quality. Same as original is the fastest.
4. Convert, preview the result on the page, and download it.

It runs entirely in your browser, so the video is never uploaded. There is no watermark, no sign-up and no fixed size limit, although very large videos are more comfortable on a computer than on a phone.

MOV to MP4, MKV to MP4, WebM to MP4

MOV to MP4

iPhone and Mac videos are usually MOV. If the video inside is H.264, converting to MP4 with Same as original only rewraps it, so it finishes in seconds with no quality loss. Recent iPhones record H.265 (HEVC) in MOV. Same as original keeps that H.265 stream, which is fast and lossless, but some older Windows computers and TVs cannot play it. If that is a problem, choose High quality to produce H.264 that plays everywhere. That step needs a browser that can decode H.265, such as Safari, or Chrome and Edge on recent Macs and Windows computers.

MKV to MP4

MKV often holds H.264 or H.265 video with AAC audio, which MP4 can carry, so the streams can be copied and the conversion is quick. If an MKV contains codecs MP4 cannot hold, those streams are re-encoded, and the summary tells you which.

WebM to MP4

WebM files use VP8 or VP9 video and Opus audio, which MP4 players do not expect. The converter re-encodes them to H.264 and AAC, and that takes noticeably longer than a MOV conversion because your device is doing real encoding work. It is normal.

MP4 to MP4

Converting an MP4 to an MP4 sounds odd, but people do it to change codec or reduce size. Use High quality to re-encode to H.264, or the video compressor if the goal is a smaller file.

Same as original, High quality or Balanced

Same as original copies every stream the new format can hold, and re-encodes only what it must. If only the video does not fit, only the video is re-encoded, at a bitrate matched to the source so it keeps its look.

High quality re-encodes everything into the format's standard codecs. Use it when a device refuses to play a file, or to turn H.265 into H.264. Balanced does the same at a lower bitrate, giving a much smaller file, which suits clips you are about to share.

What about DAT and other unusual files?

Searches like DAT to MP4 are common, but a .dat file is not one specific format. It is a generic extension used for video from old DVDs and VCDs, for data files, and for many other things. The converter does not open DAT files, so do not expect it to. If you have a .dat that is really video, a desktop media player can usually tell you what is inside it, and then you can pick the right tool for that format.

The same honesty applies to AVI, WMV, FLV and other older formats: the video converter handles MP4, MOV, M4V, WebM, MKV and MPEG-TS. If your file is in another format, a desktop converter such as a command-line tool or a media player's export function is the right route.

Also note that this is a file converter, not a downloader. It converts files you already have on your device. It cannot fetch a video from a web address.

After converting

• Too big to send? Run the result through the video compressor, or read how to compress a video without losing visible quality.
• Only need part of it? The video trimmer cuts it first, and converting a shorter file is faster. More small edits are in editing videos for free in your browser.
• Want a looping image for a chat or a document? Video to GIF has controls for frame rate, size and loop, and making a GIF from a video explains the settings.
• Not sure what is inside the file? Video Info lists its codecs, resolution and bitrate. Posting it to a social app? Why video looks worse after uploading covers what to check first.

Portrait videos and rotation

Portrait phone videos stay upright. MP4 and MOV keep the rotation flag as it is, while WebM and MKV cannot store it, so the picture is re-encoded the right way up. If a video still plays sideways, the rotate tool fixes that.