Drop WebM videos to convert to MP4Add WebM videos to convert to MP4
Browser recordings as MP4, with H.264 picture and AAC sound.
or paste with CtrlCommandV WebM
Your files never leave your deviceAbout this tool
Convert WebM to an MP4 that plays everywhere
This tool converts WebM videos to MP4 right in your browser. The VP8 or VP9 picture becomes H.264 and the Opus or Vorbis sound becomes AAC, which QuickTime, iPhones, Windows players and most editors take. It uses your browser’s own encoders and takes longer than a copy. Your videos stay on your device.
Why a WebM won’t play or import
Browsers record screens, webcams and calls as WebM, with VP8 or VP9 picture and Opus or Vorbis sound. Browsers and VLC play those, but QuickTime, many editors, phones’ gallery apps and many sites want an MP4 with H.264 picture and AAC sound.
Putting the WebM’s own picture and sound into an MP4 wouldn’t fix that, because the MP4 would still hold VP9 and Opus. So this tool re-encodes them to H.264 and AAC, the pair MP4 players take, and keeps the picture’s size, its frame rate, and the sound’s channels.
It takes longer than a copy
Re-encoding decodes every frame and compresses it again, so it takes real time. A one-minute 1080p WebM took about 11 seconds at most on a recent laptop, in every browser we tried, and a longer video takes proportionally longer. The progress bar shows how far it has got, and you can cancel.
Your video is decoded and encoded a piece at a time and the MP4 is written to your browser’s private storage as it goes, so a long video doesn’t have to fit in memory. Chrome used about 331 MB more while it ran, and Firefox about 383 MB. We haven’t measured phones.
A re-encode is a new compression of the picture, not a copy: the MP4 is made at a bitrate chosen from the picture’s size and frame rate, and its size can differ from the WebM’s.
What your browser can make
H.264 and AAC are made by your browser, not by ToolHero. In our tests Chrome made both, and so did the WebKit build Safari is based on. Firefox made the H.264 but has no AAC encoder: it keeps the Opus sound as it is and says where that may not play, instead of handing back a file presented as playable everywhere.
A WebM that can’t be converted in your browser says what is missing before you press anything, for example that it can’t make AAC sound, and another browser, such as Chrome or Safari, may make it. Older WebM files with VP8 picture and Vorbis sound convert the same way.
How it works
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Step 1:Add your WebM files
Drop screen recordings or other WebM videos here, or choose them. Each one shows what it holds and what it will become.
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Step 2:Convert
Press Convert. The picture becomes H.264 and the sound AAC. A long video takes a while, and shows its progress.
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Step 3:Save the MP4
Save it to your device, or send it from the share sheet on an iPhone or iPad.
Questions, answered
Will a WebM turned into MP4 play on my iPhone or in QuickTime?
Those are the formats iPhones and QuickTime take, and the row says before you press Convert whether your browser will make both. If your browser can’t make one of them, the row says so, and the file is never presented as playable everywhere.
Why is converting a WebM slower than converting an MKV?
An MKV usually holds H.264 and AAC, which are copied into the MP4 in seconds. A WebM holds VP8 or VP9 and Opus or Vorbis, which have to be decoded and compressed again as H.264 and AAC.
Does converting a WebM to MP4 lose quality?
A little, as with any re-encode: the picture is compressed a second time. It keeps its size and frame rate, and every frame comes through.
Why can’t Firefox make the sound AAC?
Firefox has no AAC encoder, and ToolHero doesn’t ship one because AAC is patent-encumbered. The picture still becomes H.264, and the Opus sound is kept as it is, with a note on where it may not play.
More video conversions
MP4. Picture and sound copied as they are: nothing is re-encoded.
Picture and sound copied as they are: nothing is re-encoded.MP4 · copied as it is