WebM to MP4 Converter
This is the honest one: a WebM holds VP8, VP9 or AV1 video with Opus audio, and none of those belong in an MP4 that other software will open. The picture has to be re-encoded, so it takes longer and costs a little quality — and the tool says so up front rather than after the wait.
What to know about WebM
An MP4 can technically hold VP9
It is legal, and some tools will write it. The file plays in Chrome and almost nowhere else — not in QuickTime, not in Premiere, not on a TV. A converter that took the fast path here would hand you a file with the right extension and the wrong contents, which is worse than a slow conversion.
What re-encoding costs
One generation of quality, and the time it takes to decode and re-encode every frame. Your browser's hardware encoder does the work, so it is far faster than a WebAssembly converter, but it is not the instant copy the other routes get.
If speed matters more than compatibility
Choose MKV instead of MP4. Matroska carries VP9 and AV1 natively, so the streams are copied and the job is instant — and VLC, mpv and most modern TV boxes will play the result.
What MP4 carries without re-encoding
These are the video codecs a MP4 can hold in a way other software will actually open. If your WebM already contains one of them, the stream is copied across untouched and nothing is re-compressed. Anything else is re-encoded to H.264.
H.264H.265
Need something smaller rather than something different? Compress it to a target size instead — that one aims at a file size you name.
Frequently asked questions
Why does this one take longer than the other converters?
Because it is the one that genuinely has to convert. A WebM holds VP8, VP9 or AV1 video, and none of those belong in an MP4 other software will open, so every frame is decoded and re-encoded to H.264. The other routes on this site mostly copy streams; this one cannot.
Can it not just repack it, like MOV to MP4?
An MP4 can technically hold VP9 — it is legal, and some converters will write it. The file plays in Chrome and almost nowhere else. Handing you that would mean a file with the right extension and the wrong contents, which is worse than a slower conversion.
How much quality do I lose?
One generation, the same as any re-encode. The encoder targets a bitrate matched to the source, so the difference is usually invisible at normal viewing sizes. If you need to keep the original quality exactly, convert to MKV instead — that copies the VP9 stream untouched.
Is it faster than other online converters?
Generally yes, because the encoding runs on your machine's own hardware video encoder rather than in a queue on someone else's server. There is also no upload, which for a large file is usually the slowest part of the alternatives.
What about the Opus audio?
It is re-encoded to AAC alongside the video. An MP4 can technically carry Opus, and support for it outside Chrome and Firefox is patchy enough that shipping it would defeat the point of converting to MP4 in the first place. AAC is what every player expects to find in an MP4, so that is what goes in.