How this tool works
The video is decoded and encoded again into the format you choose, then written into the matching container. MP4 with H.264 plays everywhere and is the safe choice for uploads. WebM with VP9 is smaller at the same quality. Nothing is uploaded — the work happens on your own device, through the same hardware encoder it uses to record.
Every format is tested against your browser before it is offered, and anything it cannot write is shown as unavailable rather than being offered and failing at the end of a long encode. That check matters more here than anywhere else, because codec support depends on the browser, the operating system and sometimes the graphics drivers, so a fixed list would be wrong for a good share of visitors.
Choosing a format
- MP4 with H.264 for anything you are sending someone: it plays on every device, every browser and every platform, and it is what upload forms expect. When there is no specific reason to choose otherwise, this is the answer.
- WebM with VP9 for the web, and for sound on Firefox or Linux: it is meaningfully smaller at the same quality. It is also the only way to produce a file with audio in Firefox or on desktop Linux, because those cannot encode the AAC that MP4 requires — WebM uses Opus instead, which they can.
- Converting does not restore quality: each pass decodes what is there and encodes it again, so artefacts already in the file are preserved rather than removed. Convert once, from the best source you have.
- Some formats cannot be read at all: MKV, AVI and ProRes will not open, because browsers cannot decode them. That is a limit on the input rather than the output, and it applies to every video tool here.