About the Video Converter
This video converter changes a video's format between MP4, WebM, MOV and MKV without uploading it anywhere. Pick the format you need and it checks whether the picture and sound can be moved into the new container as they are; if so, conversion is almost instant and lossless. If the new format needs different codecs, such as VP9 for WebM, the video is re-encoded using your browser's built-in encoder. You can preview the result before downloading.
Updated October 2026
How to use the Video Converter
- 1Select a video.
- 2Choose MP4, WebM, MOV or MKV.
- 3Press Convert.
- 4Wait for the progress bar to finish.
- 5Preview the result and download it.
Containers and codecs
A video file is a container (MP4, WebM, MOV, MKV) holding streams encoded with codecs (H.264, HEVC, VP9, AV1 for video; AAC, Opus, MP3 for sound). Changing the container is quick when the codecs are allowed in the new one. WebM only allows VP8, VP9 and AV1 video, so an H.264 MP4 must be re-encoded to become WebM.
- MP4: H.264, HEVC, AV1 + AAC
- WebM: VP8, VP9, AV1 + Opus, Vorbis
- MOV: like MP4, Apple's format
- MKV: almost anything
How it works without uploading
Your browser has a built-in video engine (WebCodecs) that phones and computers use to play and record video. This tool uses it through Mediabunny, an open-source media library, to read your file, change it and write a new one, all inside the page. Speed depends on your device: a recent phone or laptop handles a few minutes of HD video comfortably, while long 4K files take longer.
Speed
Copy conversions take seconds even for long videos. Re-encoding takes about as long as the video plays, depending on resolution and your device.
Which format to choose
Use MP4 for sharing with anyone: phones, TVs, social networks and every browser play it. Use WebM for web pages when you want open codecs and small files. Use MOV for editing in Apple apps like iMovie and Final Cut. Use MKV for collections played in VLC, Plex or Kodi, or to keep several sound tracks and subtitles together.
Formats the converter can read
The converter reads MP4, M4V, MOV, WebM, MKV and MPEG-TS videos, and audio files too. It can't read AVI, WMV, FLV or 3GP, which browsers don't support; HandBrake and VLC are good free desktop tools for those.
When a conversion fails
If the browser can't decode or encode a codec, the tool says which track failed. HEVC (H.265) videos from iPhones, for example, decode in Safari and Edge but not in every Firefox. Trying another browser usually solves it.
Phone and computer
Convert on any modern device; Chrome and Edge support the widest range of codecs. For web video use MP4 to WebM, and the Video Compressor makes the result smaller.
Features
- MP4, WebM, MOV and MKV
- Lossless copy when possible
- Re-encodes only when needed
- Progress bar and cancel
- Preview before download
- No upload, no watermark
Frequently asked questions
Which format should I choose?
MP4 for the widest compatibility, WebM for websites, MOV for Apple editing, and MKV for media players and archiving.
Can it convert AVI or WMV?
Not yet. Browsers can't read those older formats. Convert them with desktop software such as HandBrake or VLC.
Is anything lost when converting?
If the video and sound can be moved into the new format unchanged, nothing is lost and conversion takes seconds. If not, they are re-encoded at high quality, which takes longer.
Which browsers work best?
Chrome and Edge on computers and Android support the most video formats. Safari 16.4+ and recent Firefox work too, but some codecs, such as HEVC in Firefox, may not be supported there.
Is my video uploaded?
No. It is processed on your own device with your browser's built-in video engine, so private videos never leave your phone or computer.
Will the converted video play on my phone?
MP4 and MOV play on every iPhone and Android. WebM plays in browsers and on Android; MKV needs a player app like VLC on phones.
Can I convert just the sound?
Use Extract Audio from Video to save the sound as M4A, MP3, OGG or WAV.