Convert WebM to MP4
Drop a .webm and get an .mp4 with H.264 video and AAC audio, the combination that plays on iPhones, in Windows Media Player, in PowerPoint and in every video editor. Converted in your browser with ffmpeg, so the file never leaves your device.
Runs in your browser with ffmpeg. The file is never uploaded.
About the webm to mp4
WebM is what the browser gives you: Chrome's screen recorder, Loom and Discord clips, the MediaRecorder API and many download sites all produce it, because VP8, VP9 and Opus are royalty-free codecs the web standardised on. The trouble starts when the file leaves the browser. iPhones will not play it, Windows Media Player and PowerPoint reject it, Final Cut and Premiere need a plugin or a conversion, and most upload forms want MP4. Unlike MOV to MP4, this conversion cannot be a simple container swap: MP4 does not carry VP9 or Opus in any way players agree on, so the video has to be decoded and re-encoded to H.264 with AAC audio. This tool does exactly that with settings chosen for the typical WebM source: a quality level that is visually lossless for screen recordings and talking-head clips, even-dimension padding so odd-sized recordings do not fail, the pixel format every device accepts, and a fast-start index so the MP4 begins playing before it finishes downloading. Browser recordings sometimes have a missing duration header, which confuses many converters; ffmpeg reads them fine. Expect the encode to take about the length of the clip on a laptop, and no upload time at all.
How it works
Drop your video
MP4, MOV, WebM or MKV, up to 500MB. It is processed in your browser with ffmpeg, nothing is uploaded anywhere.
Pick the settings
Times, quality, size or speed depending on the tool. A progress bar shows how far along the export is.
Download
The result saves to your device. Free, no watermark, no signup.
Tips for best results
Things that meaningfully improve the output.
Recordings with no duration are normal
Chrome and MediaRecorder often write WebM files with no duration in the header, so the preview may show 0:00 before conversion. The output MP4 has a proper duration.
Trim first if the recording is long
WebM to MP4 always re-encodes, so time scales with length. Cut the clip in the trimmer first if only part of it matters.
Choose 1080p cap for screen recordings from 4K displays
A 4K screen capture converts four times faster at 1080p and still reads perfectly for demos and tutorials.
For editing, MP4 is the safe target
Every editor imports H.264 MP4. If the destination is Premiere, Final Cut, DaVinci or CapCut, this is the conversion you want.
Need more than webm to mp4?
renza turns photos into video with Kling, Veo and Seedance, and upscales footage to 4K. Free credits at signup, no credit card.
Create free account →Frequently asked questions
Why can I not just rename .webm to .mp4?
The extension is a label; the content is VP9 or VP8 video in a Matroska-style container. Players that do not understand it still will not play it. Real conversion re-encodes to H.264.
Does it lose quality?
It is a re-encode, so technically yes, but at the default setting the difference is not visible for screen recordings, webcam clips and most downloads.
Is my file uploaded?
No. The conversion runs entirely inside your browser using ffmpeg compiled to WebAssembly.
Does it keep the audio?
Yes. Opus or Vorbis audio is converted to AAC, which is what MP4 players expect. Silent recordings produce a silent MP4.
How long does it take?
About real time for 1080p on a laptop: a 2-minute clip takes 1-3 minutes. Phones are slower. The progress bar shows where it is.