RunToolRunWebM to MP4
Convert WebM files to MP4 format.
How to Convert WebM to MP4
Select a WebM file
Click the upload area or drop the .webm video — screen recordings are the most common source.
Re-encoding in your browser
The VP8/VP9 video is re-encoded as universally compatible H.264 MP4 on your device.
Download the MP4
Save a video ready for editors, phones, TVs and every sharing platform.
This one always re-encodes
WebM carries VP8, VP9 or AV1 video with Vorbis or Opus audio. MP4 in practice means H.264 with AAC. There is no overlap, so unlike a MOV to MP4 remux, the streams cannot be copied — every frame has to be decoded and encoded again.
That has two consequences worth knowing before you start. It takes real time, particularly in a browser where the encoder is single-threaded. And it costs a generation of quality, because a lossy source is being re-compressed by a different lossy codec.
The file usually gets larger
VP9 and AV1 are newer and more efficient than H.264, so the same visual quality needs fewer bits in WebM than in MP4. Converting therefore tends to produce a bigger file that looks slightly worse — a genuinely bad trade in isolation.
It is still the right move when the destination cannot handle WebM, which remains common. Video editing software, presentation tools, messaging apps, older devices and a great many upload forms accept MP4 and nothing else. You are buying compatibility, and there is no way to buy it cheaply here.
Where WebM files come from
Browser-based screen recorders, video calls, streaming downloads and open-source tools all produce WebM, because it is royalty-free and browsers encode it natively. So the format arrives most often exactly when someone has recorded something they now need to send to a colleague or upload somewhere.
If you control the recording, checking whether the tool can record MP4 directly avoids the whole conversion and the quality it costs. Converting is the fallback for files you have already got, not a step worth building into a workflow.
Transparency and running it locally
WebM supports an alpha channel and MP4 in its normal H.264 form does not. A WebM with a transparent background converts to a video with that transparency flattened, usually to black. If the transparency is the point, MP4 is the wrong destination.
Encoding runs through a WebAssembly FFmpeg build in your browser, so screen recordings of internal systems and personal calls stay on your machine. Being single-threaded, it is markedly slower than a desktop encoder — reducing resolution or trimming length before converting is the difference between a minute and a long wait.
Keeping the quality loss small
Since a re-encode is unavoidable, the aim is to spend enough bits that the second generation stays invisible. Encoding at a generous quality setting and keeping the original resolution costs some file size and preserves the detail; compressing hard to save space on top of an already-compressed source is what produces the mushy result people associate with converted video.
Screen recordings are the exception worth noting. Interface footage is mostly flat colour and sharp text, which H.264 handles less gracefully than VP9 did, so text can visibly soften. If the recording exists to demonstrate an interface, encode it generously or keep the WebM for anywhere that accepts it.