Convert WebM to MP4

Where WebM files come from

Web pages that record video in Chrome, Edge or Firefox have long saved it as WebM, so the files usually come from something that ran in a browser: an online screen recorder, a webcam or microphone test, a meeting or interview tool that records in the page, or a web app with a download button for its recordings. Browser extensions that record a tab or the whole screen often save WebM as well, and some sites offer their clips in it.

Google introduced WebM in 2010 as an open format for the web, releasing the VP8 codec openly at the same time so any browser could support it without license fees. It holds VP8, VP9 or AV1 video and Opus or Vorbis sound. Browsers, Android and VLC play it; many video editors, iPhones, TVs and upload forms do not, which is when an MP4 is needed.

Copy or convert: As it is versus High

MP4 is allowed to hold VP9 and AV1, so As it is moves those pictures across untouched, instantly and with no loss. The result is a genuine MP4, but programs and devices that ask for MP4 usually expect H.264 inside, and many will still refuse it. With High you get an H.264 picture and AAC sound in every case, the safe combination. Choose As it is only when you know your player handles VP9 or AV1. Not sure which codec a file has? Its row names it before you convert.

Settings for screen recordings

A screen recording is mostly sharp text and still areas. High keeps small writing crisp; Balanced, at about half the size, is fine for a webcam talking head. Under More settings:

• Frames a second: 30 or even 15 is plenty for slides and software walkthroughs and makes a lighter file. Octoolo only ever lowers it.
• Size: a recording of a large monitor can come down to 1080p or 720p.
• Channels: Mono suits a single voice.
• Keep the sound: switch it off for a silent MP4 when the recording only picked up hum.

To cut the dead seconds at the start and end, convert first and then trim the MP4 in the Video Editor. Still to record? Octoolo's own screen recorder saves MP4 from the start, so there is nothing to convert afterwards.

What size to expect

VP9 and AV1 squeeze more picture into each megabyte than H.264 does, so at High a VP9 or AV1 WebM usually becomes a somewhat larger MP4. VP8 is about as efficient as H.264, and sizes stay close. High never makes a file needlessly bigger than its original, and Small is there for recordings that only need watching once, such as a bug report. The sound changes too: High gives AAC 256 kbps for stereo and 128 for mono, usually more than a browser spent on it, while Balanced and Small use less.

Re-encoding is the slow part. NVIDIA, AMD and Intel graphics chips take it on when they have a video encoder; on a PC without one, Windows' encoder or the processor steps in. One such conversion runs at a time, and the list shows its speed and the time it has left.