Why does my WebM show 0:00 duration?

Browser recorders write the file while recording and never go back to fill in the length. The converted MP4 has correct duration and seeking.

Is the conversion lossy?

Yes, VP9 to H.264 is a re-encode. At High quality it is visually transparent for screen content.

Can I keep the transparent background of a WebM?

MP4/H.264 does not support alpha. Use GIF or keep WebM for transparency.

Video Converters

WebM to MP4

Web-based recorders save WebM, which iMovie, Premiere, phones and many upload forms refuse. Convert to a standard H.264 MP4.

Runs in your browser when it can; large or unusual files use our EU server and are deleted within 1 hour.

Drop WebM files here

or click to browse · paste from clipboard · up to 4000 MB each

Select files

Options

Quality

Resolution

Frame rate

Why convert WebM to MP4

WebM uses VP8/VP9 video and Opus audio — great for browsers, unsupported almost everywhere else. Unlike MOV or MKV, a WebM has to be re-encoded to become an MP4, which this tool does with the browser’s hardware-accelerated encoder.

Screen recordings from the MediaRecorder API often lack a duration header and can appear as “0:00” in players; the conversion fixes the metadata so the MP4 seeks and shows its length correctly.

How it works

Drop WebM file onto the box above, click it to browse, or paste from the clipboard.
Adjust the options if you need to — the defaults suit most cases.
Press Convert. Small files are handled on your device; larger ones are sent to our server with a progress bar.
Download the MP4 — individually or all at once.

About the formats

WebM · WebM video · .webm

The royalty-free web video format (VP8/VP9/AV1 video, Vorbis/Opus audio) produced by browser screen recorders, Discord and many online tools.

WebM is based on Matroska and plays in every browser, but not in iMovie, Premiere or on most phones without conversion.
Browser recording APIs output WebM, which is why screen recordings from web apps come as .webm.
WebM to MP4 requires re-encoding the video, because MP4 does not carry VP9 widely.

MP4 · MPEG-4 Part 14 video · .mp4

The video format that works everywhere: phones, TVs, browsers, social networks. Normally H.264 video with AAC audio.

MP4 is a container; the codec inside (H.264, HEVC/H.265, AV1) decides what can play it.
H.264 MP4 is the safe choice for uploads and sharing; HEVC MP4 from newer iPhones needs extra codecs on Windows.
The “moov atom” placement decides whether a browser can start playing before the whole file downloads.

Related conversions

MP4 to WebMOn-deviceMP4 to smaller WebM (VP9/Opus) for websites.MKV to MP4PopularMKV to MP4 by remuxing, lossless and fast.Compress VideoPopularMake a video small enough for email, WhatsApp or uploads.MP4 to GIFPopularOn-deviceVideo clip to an animated GIF with trim and size controls.Video ConverterAny video format to any other, with codec options.MOV to MP4PopulariPhone/Mac MOV to MP4, usually without re-encoding.

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