Video Format Converter
Convert video between MP4, WebM, MKV, MOV and AVI — or pull out an audio track or an animated GIF — without uploading a single byte.
Convert with this tool
or choose a file from your device — it is processed in this tab and never uploaded
Accepted: MP4, MOV, MKV, AVI, WebM, M4V, MPEG-TS, FLV, WMV, 3GP
Files stay on your device. There is no upload, no queue and no watermark, so a conversion works even with the network switched off after the page has loaded.
Supported formats & processing
| Accepted input | MP4, MOV, MKV, AVI, WebM, M4V, MPEG-TS, FLV, WMV, 3GP |
|---|---|
| Produced output | MP4 (H.264 + AAC), WebM (VP9 + Opus), MKV, MOV, AVI, animated GIF, MP3, WAV |
| Processing | FFmpeg.wasm (video engine, downloaded on first use) |
| Upload required | No — the file is read locally and never transmitted |
How to use this tool
- Add the video fileIts size is shown immediately so you know what you are working with.
- Choose the output containerMP4 for universal compatibility, WebM for open web delivery, MKV to keep multiple streams.
- Set the quality with the CRF sliderLower numbers mean better quality and larger files. CRF 23 is a good balance.
- Adjust resolution and frame rate if neededDownscaling to 1280 px wide is usually the single biggest size saving.
- Convert, then preview and downloadThe result card compares the source and output sizes.
About this tool
Video formats are containers, and containers hold streams encoded with specific codecs. That is why a file extension alone never tells you whether a device will play something: an MP4 with H.264 video and AAC audio plays nearly everywhere, while an MP4 with ProRes video plays almost nowhere outside a Mac.
This converter gives you control of both layers. Choose the container, then choose the quality, the resolution, the frame rate and the audio bitrate. Native formats are handled with the browser's own decoders; everything else runs through the FFmpeg engine compiled to WebAssembly, which is downloaded once and then cached for the session.
Features
- MP4, WebM, MKV, MOV, AVI, GIF, MP3 and WAV output from one page
- Real H.264 and VP9 encoding through FFmpeg.wasm
- CRF quality control with a plain-language explanation of each setting
- Resolution downscaling, frame-rate conversion and audio bitrate control
- Optional trimming to a time range in the same pass
- Source and output sizes compared so the saving is visible
Frequently asked questions
Which format should I convert to?
MP4 with H.264 and AAC is the safest answer for sharing, uploading or playing on a television. WebM is better for the open web. MKV is best when you want to keep several audio or subtitle tracks together.
Why does the first conversion take longer?
The FFmpeg engine is about 25 MB of WebAssembly and JavaScript. It is downloaded on the first job and cached for the rest of the session, so subsequent conversions start immediately.
Does converting video reduce quality?
Any re-encode does, but the loss is controlled by the CRF setting. CRF 18 is close to visually lossless; CRF 28 is a good size/quality compromise. Converting without re-encoding is only possible when the codecs already match.
Can I convert a video that is larger than my available memory?
The whole file is held in memory during processing. Very large files — several gigabytes — need a desktop machine with plenty of RAM, or a desktop FFmpeg build.