Why won't my WebM play on an iPhone or in my editor?

WebM uses codecs that iPhones, QuickTime, and many editors don't support. The MP4 from this page uses H.264 video, which they all open.

Is WebM to MP4 lossless?

No. The video is re-encoded to H.264 at a high quality, so the picture changes slightly and the file can be larger than the WebM.

WebM to MP4

Convert a WebM video to MP4 for phones, editors, and social apps. Processing stays on your device.

Files stay on your device

Drop a file to convert

See its format, then choose an output.

Any media file this browser’s engine can read.

How to convert WebM to MP4 online

Open a WebM, such as a screen recording or a downloaded clip, and export an MP4 that iPhones, editors, and social apps open. The WebM to MP4 converter re-encodes the VP8, VP9, or AV1 video to H.264 and the audio to AAC in your browser, without uploading the file.

Step 1
Choose your WebM
Pick a file or drop it into the converter above.
Step 2
Keep MP4
MP4 is selected; choose another format if you need one.
Step 3
Download the MP4
Save the H.264 MP4 when it is ready.

What to expect

Supported inputs: WebM videos, including browser screen recordings, and other readable video files.
What happens: Video is re-encoded to H.264 and Opus or Vorbis audio to AAC, the codecs MP4 players expect. H.264 video and AAC audio already in the file are copied.
Limits: Re-encoding takes longer than copying and depends on your device. Firefox can't encode AAC, so its MP4s carry Opus audio instead.

Private by design

Your video stays on your device

Mastershot processes your file locally in this browser. It does not need to be uploaded to a server, and you do not need an account to use the tool.

No upload
No signup
No watermark