Updated July 2026
About this tool
WebM is the open, web-first container behind most browser screen recordings — Chrome's recording APIs, OBS, Loom and Discord clips all produce it. It pairs VP8 or VP9 video with Opus or Vorbis audio: excellent codecs for the web, but ones Apple's QuickTime, older iPhones and editors like Premiere often refuse to open.
Unlike our MOV and MKV converters, this one is a true transcode rather than a remux: VP8/VP9 video is re-encoded to H.264 and the audio to AAC, because VP9-inside-MP4 playback support is too patchy to rely on. Re-encoding is CPU-bound, so speed depends on the clip length and your device — but the result is an H.264/AAC MP4 that plays practically everywhere, from Windows and Android to iPhones and editing software.
Conversion runs in a Web Worker in your browser — videos are never uploaded.
Frequently asked questions
Why do WebM files need re-encoding instead of a lossless remux?
Because of codecs, not containers. WebM holds VP8 or VP9 video, and while VP9 can technically sit inside MP4, very few players accept that combination. To produce an MP4 that actually plays everywhere, the video is transcoded to H.264 and the audio to AAC — a real re-encode, unlike our MOV/MKV remux path.
Will the converted MP4 lose quality?
Slightly, in theory. Transcoding is a generational re-encode, but the tool uses a high-quality H.264 setting, so the difference is rarely visible. If the output looks soft, your source was likely low-bitrate to begin with — screen recordings compress very well and typically look identical.
Why won't my WebM open in QuickTime, iPhone or Premiere?
WebM is a web-first format used by Chrome screen recorders, OBS, Loom and Discord clips. Apple software and many editors never licensed or shipped VP8/VP9 support, so the file is rejected even though it isn't corrupted. Converting to H.264 MP4 fixes playback everywhere.
Is my video uploaded during conversion?
No. Everything runs locally in your browser using its built-in codecs (WebCodecs) — the file never leaves your device. Conversion speed therefore depends on your hardware and the video length, not on an upload queue; there are no server-side size limits either.