Convert WebM to MP4
100% private — runs on your device, never uploaded. Works offline once loaded.
WebM is the format the web hands you — a saved video from a browser, a screen recording from a web app, a clip pulled out of a page — and it is built on VP8 or VP9 video with Vorbis or Opus sound. None of those are codecs MP4 can carry, so unlike MOV or MKV this conversion genuinely re-encodes: the picture is rebuilt as H.264 and the sound as AAC. That is the price of a file that will open in Premiere, play on an iPhone, and upload to platforms that quietly reject WebM. Pick High quality if the clip matters, since re-encoding always costs a little.
Frequently asked questions
Why is WebM to MP4 slower than MKV to MP4?
Because it cannot be a rewrap. VP8 and VP9 are not codecs MP4 carries, so every frame has to be decoded and encoded again.
Will it look worse?
Slightly, in principle — it is a second generation of lossy encoding. At High quality the difference is not visible in normal viewing.
Is anything uploaded?
No. FFmpeg runs inside the page, so the video stays on your device.
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