Convert Video
Convert videos between MP4, WebM, MKV and other formats.
First use downloads FFmpeg (~30 MB). It's cached after that.
About this tool
The video converter transforms files between MP4, WebM, and MKV formats directly in the browser, without installing any software or uploading files to external servers. Processing runs locally using ffmpeg.wasm, keeping your videos completely private.
To convert, select the video file and choose the desired output format. MP4 uses the H.264 codec for maximum compatibility; WebM uses VP9, ideal for the web and modern browsers; MKV is a flexible container that preserves original streams without codec re-encoding. After selecting the format, click convert and wait for processing to complete.
Situations that require format conversion include: some devices and platforms only accept MP4 but your file is in WebM or MKV; specific video editors prefer certain containers; streaming platforms have their own technical requirements; or you need a more universally compatible format to send a video to someone using a limited player.
It is worth noting that conversions involving re-encoding (such as WebM to MP4) introduce some quality loss, as the video goes through a decode-then-encode cycle. Conversions using stream copy (such as to MKV) are near-instant and lossless. For general use, MP4 remains the format with the broadest universal compatibility.
Frequently asked questions
Is my video uploaded to any server during conversion?
No. All processing happens locally in the browser with ffmpeg.wasm. No data is transmitted.
Is the tool free?
Yes, completely free, no account required, no usage limits.
Does it work on mobile?
Yes, on modern browsers for Android and iOS. Larger files may take longer to process.
Which format should I choose?
MP4 is the most compatible option for most cases. WebM is ideal for the web. MKV is recommended when you want to preserve multiple audio tracks or subtitles.
Is there any quality loss during conversion?
It depends on the output format. Conversions to MP4 and WebM involve re-encoding with minimal quality loss. MKV preserves the original streams without re-encoding.