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Convert WebM to MP4

Convert WebM screen recordings and downloads into H.264 MP4 videos that play on iPhone, Windows and in editing apps; the video is converted on your device.

Drop videos to convertMP4, MOV, MKV, WebM, AVI and more · up to 3 files at once free
Choose videosProcessed on your device — never uploaded
Runs in your browser · no uploadHow it works

How to use WebM to MP4

  1. 1

    Drop the WebM files

    Add up to 3 .webm videos — browser screen recordings, Loom or Google Meet exports, web downloads — up to 500 MB and 10 minutes each.

  2. 2

    Pick a quality

    High keeps the look of the original; Balanced and Small give lighter files. Lower the resolution for long screen recordings.

  3. 3

    Convert to MP4

    Every frame is re-encoded to H.264 and the sound to AAC; the progress bar shows the time left.

  4. 4

    Download

    Save name.mp4 for iPhone, PowerPoint, WhatsApp or any editor.

Limits and Pro

Up to 3 WebM files per batch, each up to 500 MB and 10 minutes long.

Pro converts up to 500 WebM recordings per batch, each up to 4 GB and 10 hours. See Pro

About WebM to MP4

WebM is the web's open video format, built on Google's VP8, VP9 or AV1 video codecs and Opus or Vorbis audio. Browsers produce it whenever they record — screen recorders, the MediaRecorder API, many meeting and voice tools — and YouTube and other sites serve it. Outside the browser it is less welcome: iPhone Photos and QuickTime, PowerPoint, many Windows apps, WhatsApp, Instagram uploads and older TVs expect MP4 with H.264.

That is why this page doesn't just rewrap the streams. A WebM's VP9 video could be copied into an MP4 box, but the result still wouldn't play on an iPhone, so the video is decoded and re-encoded as H.264 and the Opus or Vorbis sound becomes AAC at 160 kbps. Your browser's hardware encoder does the work through WebCodecs when it can, which is often faster than real time; otherwise ffmpeg.wasm takes over, slower but able to read any WebM. Recordings made by MediaRecorder often lack a duration in the file header; the converter measures it so progress and the result are correct.

A re-encode can't add quality. Screen recordings with small text look best at the High setting and their original resolution; for long recordings, 720p keeps text readable at a much smaller size. Transparent WebM video (VP9 with alpha) loses its transparency, since H.264 MP4 has none. Only the first video and audio track are converted.

Privacy

WebM decoding and H.264 encoding happen in this tab, either with WebCodecs through mediabunny or with ffmpeg.wasm in a Web Worker. Screen recordings often show private information, and none of it is uploaded; only the 31 MB ffmpeg engine may be fetched from jsDelivr, without any of your data.

WebM to MP4: frequently asked questions

Why does WebM to MP4 take longer than MOV to MP4?
Because the video has to be re-encoded. MOV files from phones already contain H.264 or HEVC, which MP4 players understand, so they are only repackaged. WebM uses VP8, VP9 or AV1, which iPhones and many apps can't play from an MP4, so every frame is decoded and compressed again as H.264. With hardware encoding a minute of HD video typically takes well under a minute.
Will my screen recording stay sharp?
Keep the High quality setting and the original resolution, and text and interface details stay crisp. Only reduce the resolution for long recordings you need to share quickly: 720p is still readable for most interfaces, while 480p blurs small text noticeably.
Can I play the MP4 on an iPhone and in PowerPoint?
Yes, that's the point of converting. The result uses H.264 video and AAC audio, the combination iPhone, iPad, Mac, Windows Media Player, PowerPoint, Keynote, WhatsApp and all social networks support. Insert it into a slide or AirDrop it to a phone and it plays without any extra codec.
My WebM shows no length in other players. Will the MP4?
Yes. Files recorded in a browser are written while recording, so their header often has no total duration and players can't show a progress bar or seek. The converter works out the real length while reading the file, and the MP4 it writes has a proper duration and an index at the start, so it seeks instantly and streams from the first second.
What happens to transparency in a WebM?
It is lost. Some animated stickers and overlays are VP9 WebM with an alpha channel, but H.264 MP4 has no transparency, so the see-through areas become a solid colour, usually black. If you need the transparency, keep the WebM for websites and apps that support it, and convert only copies meant for phones, slides or chats.

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