Video Converter
Convert videos between MP4, WebM, MKV, MOV and MP3 entirely in your browser.
Maintained by Aygul Dovletova
How to Use the Online Video Converter
- Drop or pick a video - MP4, WebM, MOV, MKV or any format the browser can decode. Files stay on your device, nothing is uploaded.
- Choose a target format - MP4, WebM, MKV, MOV or MP3 audio-only. The converter detects your source format and picks the fastest path automatically.
- Pick a quality preset - Default produces a smaller, share-friendly file. High keeps more visual detail at the cost of size.
- Click Convert - ffmpeg.wasm runs the encode locally. You can cancel mid-conversion and the worker is terminated within two seconds.
- Preview and download - the result plays inline. Use the Download button to save the converted file.
What This Tool Does
This is a free, browser-based video converter that swaps formats between MP4, WebM, MKV, MOV and MP3 without uploading the source file. The conversion runs entirely on your machine using a WebAssembly build of ffmpeg, so private screencasts, work demos, family videos and anything under NDA stay private.
It is built for the everyday cases that drive most search traffic: convert MP4 to WebM for the web, convert MOV to MP4 for iPhone clips that other devices refuse to play, convert MP4 to MP3 to extract audio, and convert MKV to MP4 for the same playback issue. It is not a transcoding farm and it is not a replacement for desktop ffmpeg, but for short clips up to a few hundred megabytes it does the job in your browser tab.
Why Convert Video Format in the Browser
Most online video format converters upload your video to a third-party server, run the encode there, and email or display a download link. That is a bad default for screen recordings of internal tools, presentations under NDA, family photos or any clip you would not want sitting on someone else's disk. A browser-based converter avoids that risk: the binary never leaves your computer and there is nothing for a third party to keep, lose or leak.
The trade-off is that ffmpeg.wasm is bigger than a server-side ffmpeg - the worker plus core assets are roughly 30 MB on first load. Modern browsers cache the assets, so the second visit is near-instant. For most short clips the encode itself completes in under a minute on a recent laptop. For long clips, a desktop tool will still be faster.
Supported Formats and How They Are Encoded
- MP4 (H.264 + AAC) - the default playback format almost everywhere. Re-encoded with libx264 (preset veryfast, CRF 23 default / 18 high) and AAC audio.
- WebM (VP9 + Opus) - the open web format. Re-encoded with libvpx-vp9 at 1 Mbps default / 2 Mbps high and Opus audio. Slower than MP4 due to VP9 cost; we use the realtime deadline to keep encode time reasonable.
- MKV (H.264) - Matroska container. When the source is already H.264 family (MP4, MOV, MKV) we stream-copy the video track without re-encoding, which is fast and lossless.
- MOV (H.264) - QuickTime container. Same stream-copy fast path as MKV when the source is H.264 family.
- MP3 (audio only) - extract the audio track and encode it with libmp3lame at 192 kbps default / 320 kbps high. The video track is dropped.
Convert MP4 to WebM, MP4 to MP3, MOV to MP4 and More
The most common conversions and how the tool handles them:
- MP4 to WebM - re-encode to VP9. Useful for embedding video on the web where Chromium browsers prefer WebM and you want a smaller file than a baseline MP4.
- MP4 to MP3 - drop the video, encode audio to MP3. The fastest path of all conversions since there is no video re-encode.
- MOV to MP4 - container change inside the H.264 family. Stream-copy is used so this completes in seconds even for large files.
- MKV to MP4 - same stream-copy fast path, useful for files that did not come from an iPhone but still need MP4 for playback.
- WebM to MP4 - re-encode video from VP9 to H.264. The slowest path because both legs are heavy codecs, but the result plays everywhere.
- MP4 to MOV - stream-copy container change for iPhone or QuickTime workflows.
How the Conversion Works Under the Hood
For an MP4 to MP3 audio extraction the tool runs ffmpeg -i input.mp4 -vn -acodec libmp3lame -b:a 192k output.mp3. For a MOV to MP4 container change it runs ffmpeg -i input.mov -c copy output.mp4 which is essentially a remux and finishes almost instantly. For an MP4 to WebM full re-encode it uses ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 1M -c:a libopus -b:a 128k -deadline realtime -cpu-used 5 output.webm.
The tool detects the source format from the file extension and selects the right pipeline automatically. You see the result of that choice in the helper text above the Convert button so it is obvious whether the conversion will be a fast remux or a full re-encode.
Use Cases for the Free Online Video Converter
- iPhone users - convert MOV recordings to MP4 so Windows, Android and the wider web play them without a separate codec install.
- Web teams - convert MP4 clips to WebM for HTML5 video tags, smaller payloads on Chromium browsers and broader codec coverage.
- Audio podcasters - extract audio from a video shoot or screen recording as MP3 ready for editing in Audacity, Audition or your DAW of choice.
- Educators and trainers - convert long-form lecture recordings between containers for upload to LMS platforms with codec restrictions.
- Engineering teams - turn an MKV screen recording into an MP4 for ticket attachments and Slack messages without uploading to a third party.
- Streamers and content creators - quick remuxes between MOV, MP4 and MKV to fit the upload requirements of YouTube, Twitter, TikTok and Discord.
- Privacy-conscious users - any conversion that touches sensitive footage stays on your device. No third party ever sees the file.
Tips for a Smaller, Cleaner Converted Video
- Pick the Default quality preset unless you really need to preserve every detail. The High preset roughly doubles file size.
- For sharing in chat apps, MP4 with default quality is almost always the right answer. WebM is smaller but not all clients play it.
- If you only need the audio, pick MP3 directly. It is much faster than converting to a video format first and then extracting audio.
- Trim the source video first if you only need part of it. The Video Trimmer tool on this site is built for exactly that.
- Avoid format-converting twice in a row. Each lossy re-encode loses quality. Pick the final target up front.
Privacy and Browser Support
The tool runs in a cross-origin-isolated context (COOP/COEP enabled site-wide) so the multithread build of ffmpeg.wasm can use SharedArrayBuffer. That means it works in recent Chrome, Edge and Firefox on desktop, and on Android. Older Safari versions, mobile Safari without iOS 16.4+ and embedded webviews may not enable cross-origin isolation; in those cases the tool surfaces a clear "Browser not supported" message instead of silently failing.
Your video file is read into memory with ArrayBuffer, written into the ffmpeg virtual filesystem, processed and then deleted. The output Blob and its blob: URL are scoped to the page and revoked when you reset the tool or navigate away. None of the data leaves your browser at any point.
Frequently Asked Questions
How do I convert MP4 to WebM online for free?
Open this page, drop your MP4 into the upload box, pick WebM as the target format and click Convert. The video format converter runs entirely in your browser - the file never uploads to a server. Default quality produces a smaller share-friendly WebM. Use High if you are publishing the result and need extra detail.
How do I convert MP4 to MP3 to extract audio?
Drop your MP4 file, choose MP3 as the target format and click Convert. Only the audio track is encoded - the video is discarded - so this is the fastest path of all the conversions on offer. The default 192 kbps preset is fine for podcasts and voice. The High preset bumps to 320 kbps for music.
How do I convert MOV to MP4 from an iPhone recording?
Drop the MOV file and pick MP4 as the target format. Because both formats are H.264 family, the converter stream-copies the video track without re-encoding, which finishes in seconds and keeps the original quality. Use this path whenever you need iPhone footage to play on Windows, Android or older Macs.
Is the online video converter really free with no upload?
Yes. Conversion runs locally with ffmpeg.wasm, a WebAssembly build of ffmpeg. There is no signup, no watermark, no daily limit and no upload. Open DevTools - Network while you convert and you will see only the initial page load and ffmpeg core assets. Your video bytes stay on your device.
What is the maximum video file size I can convert?
The tool caps the input at 500 MB to stay within the WebAssembly memory budget that browsers reliably support. For longer or larger clips, trim the video first or wait for the Tier-3 backend coming with the monorepo refactor. In practice, screen recordings under five minutes at 1080p sit well within the limit.
Why is the WebM conversion slower than MP4?
VP9 is a much heavier video codec than H.264. We pick the realtime deadline and a faster cpu-used setting to keep encode time bearable, but for the same input WebM still takes two to four times longer than MP4. If you do not specifically need WebM, pick MP4 - the result plays in more places and finishes faster.
Why is the first conversion slow?
The first time you open the tool, your browser downloads the ffmpeg.wasm core (about 30 MB) and the worker script. After that the assets are cached on disk. Subsequent visits start almost instantly. The encode itself runs on a worker thread so the page stays responsive.
Why does the browser say "not supported"?
ffmpeg.wasm threads need a cross-origin-isolated context, which requires the page to be served with COOP and COEP HTTP headers. Most modern desktop browsers and recent mobile Safari handle this correctly, but extension webviews and very old browsers may not. If you see the unsupported message, try the same link in a recent Chrome, Edge or Firefox window.
Can I cancel a long conversion?
Yes. Click Cancel during the encode and the ffmpeg worker is terminated within about two seconds. The page returns to the file-selected state so you can adjust settings and retry without re-picking the file.
Why does converting between MP4, MOV and MKV finish so fast?
Those three formats are all H.264 family containers in the typical case. The converter detects this and uses ffmpeg stream-copy (-c copy) which remuxes the existing video track into the new container without re-encoding. Apart from a tiny disk write the operation is essentially free.