Convert video between formats, without uploading it
Drop in as many files as you like, choose an output format, and press Render. The tool converts between MP4, MKV, MOV, AVI, GIF, ProRes, MXF, transport streams and two dozen other formats, and it can pull the audio out as MP3, M4A, WAV, FLAC or OGG. It is free, needs no account, adds no watermark, and has no file size limit beyond what your own machine can hold.
Nothing is uploaded. A real build of FFmpeg, compiled to WebAssembly, runs inside the tab and reads your files straight off your disk. You can confirm it by loading the page, disconnecting from the network, and converting anyway — it works offline.
Everything defaults to leaving your file alone
Resolution, frame rate, audio codec, channel count and sample rate all start on same as original, and that means the setting is genuinely not applied rather than applied with a value the tool picked. Where the container allows it, the original audio track is copied through untouched instead of being re-encoded — so converting an MKV to an MP4 does not quietly cost you a generation of audio quality.
Everything you might want to change — quality, codecs, bitrate, resolution, frame rate, trimming and raw FFmpeg arguments — is in Advanced settings, closed by default because the defaults are already the right answer for most conversions.
How it works
- Add your files. Drop them in or click to browse. The list shows each file's real resolution, length and codecs as it reads them.
- Pick an output format. The common ones are at the top of the list; professional, legacy and alpha formats are grouped below.
- Press Render. Files convert one at a time. On Chrome and Edge you can choose an output folder first and finished files are written straight into it; in other browsers each one gets a Download button.
Output formats
| Group | Formats | Best for |
|---|---|---|
| Common | MP4, MKV, MOV (all H.264), AVI, GIF | Everyday conversion, sharing and web use. MP4 with H.264 plays on essentially anything. |
| Audio only | MP3, M4A, WAV, FLAC, OGG | Pulling the sound out of a video, or converting between audio formats. |
| Alpha | MOV ProRes 4444 | Keeping transparency a file already has. It does not create transparency — for that, use the greenscreen remover, which can also export transparent WebM. |
| Professional | ProRes 422 / HQ / LT / Proxy / 4444 XQ, MXF, FFV1, HuffYUV, MJPEG, TS, M2TS | Editing masters, broadcast delivery and archival preservation. |
| Legacy | WMV, FLV, 3GP, OGV, VOB, MPG, DV | Older players, DVD authoring and hardware that will not take anything newer. |
Questions
Are my videos uploaded?
No. There is no server to upload to. The tool downloads a copy of FFmpeg the first time you convert something, and from then on all the work happens in your browser. Your files never leave the machine.
Why is it slower than FFmpeg on my desktop?
Because it is FFmpeg compiled to WebAssembly rather than native code, and a browser tab gets a fraction of the CPU a desktop build would. Expect a few times slower than native. Two things help a great deal: leave resolution and frame rate on same as original, which lets the job run on the faster multithreaded engine — it is around six times quicker — and trim long clips down to the part you actually need.
How big a file can it handle?
Up to a couple of hundred megabytes is comfortable. Larger files work but get slow, and very large ones can exhaust the memory a browser tab is allowed. Trimming is the reliable fix — it reduces both the time and the memory.
Can I export video with transparency?
If you specifically need a transparent WebM, the greenscreen remover can export one — it encodes with your browser's own video encoder rather than with FFmpeg, which is why it can.
Will it keep my audio quality?
Wherever the output container can carry the original audio track, the track is copied across untouched rather than re-encoded — the row tells you which happened. When the container cannot take it (WebM only accepts Opus and Vorbis, for instance) the audio is re-encoded with that format's standard codec. You can always force a specific one in Advanced settings. Note that changing the channel count, sample rate or bitrate makes a copy impossible, so setting any of those re-encodes the track by definition.
Does it work on a phone?
It loads and it will convert short clips, but video encoding is heavy and mobile browsers cap memory hard. A desktop browser is much better for anything longer than a few seconds.