Video Converter: MP4, WebM, MOV in Browser
Convert MP4, WebM, and MOV video files in your browser using ffmpeg.wasm. No upload needed.
Upload a video in any common format, pick a target container (MP4, WebM, or MOV), and convert in one click. The encode runs entirely via ffmpeg.wasm inside your browser tab, so the file never leaves your device. MP4 and MOV output uses H.264 video with AAC audio. WebM output uses VP9 with Opus audio, which is slower but produces files optimized for web playback.
Video Converter uses ffmpeg.wasm, the WebAssembly build of FFmpeg, to transcode between MP4, WebM, and MOV without sending your file to a server. MP4 and MOV output encodes video with libx264 at CRF 23 (high quality) and audio with AAC at 128 kbps, which gives a widely compatible result across browsers, phones, and desktop players. The two differ only in container format: MOV is Apple's QuickTime wrapper and plays natively on macOS and iOS, while MP4 uses the ISOBMFF container and is accepted by nearly every player and platform.
WebM output uses the VP9 codec for video and Opus for audio. VP9 achieves good compression at lower bitrates, making WebM files well-suited for web delivery, but the VP9 encoder running in WebAssembly is significantly slower than libx264. The realtime deadline and cpu-used=5 flags trade a little compression efficiency for speed, but converting a long clip to WebM may still take several minutes on a typical laptop. A progress indicator tracks the encode. For time-sensitive work, MP4 is the faster choice.
The tool detects the source file extension and shows it next to the filename. After conversion the result size is displayed alongside the source size. The download filename matches the original name with the new extension. Object URLs are revoked when a new file is loaded and when the component unmounts.
- 1
Upload a video
Click Choose file and pick any MP4, MOV, WebM, MKV, or AVI file. A preview plays inline and the source format is shown.
- 2
Pick a target format
Select MP4, WebM, or MOV from the output format dropdown. A note appears when WebM is selected to warn that VP9 encoding takes longer.
- 3
Convert and download
Click Convert video. FFmpeg.wasm loads on first use, encodes the file locally, and presents a preview and download link when done.
Convert MOV to MP4 for sharing
QuickTime MOV files from an iPhone or Mac often fail to play on Windows or Android. Convert to MP4 for universal compatibility.
Prepare a video for a web page
Convert an MP4 to WebM to add a second source in a video element, so browsers that prefer WebM can use the smaller VP9-encoded file.
Convert WebM to MP4 for editing
Screen recordings and browser-captured clips are often saved as WebM. Convert to MP4 before importing into video editors that do not support WebM.
Get a MOV file from an MP4
Some Apple workflows and Final Cut Pro projects expect MOV containers. Convert an MP4 to MOV without re-uploading to an online service.
Is my video uploaded to a server?
No. The file is read into ffmpeg.wasm's in-memory filesystem and processed entirely by WebAssembly running in your browser tab. No data is sent over the network.
What is the difference between MP4, WebM, and MOV?
MP4 (ISOBMFF) is the most universally compatible container and plays on nearly every device and platform. WebM uses VP9 video and Opus audio, which are royalty-free codecs optimized for web delivery. MOV is Apple's QuickTime container and is the native format on macOS and iOS. All three here use the same H.264 video (for MP4/MOV) or VP9 (for WebM).
Why is WebM conversion so much slower?
H.264 (libx264) encodes very efficiently in WebAssembly. VP9 (libvpx-vp9) is a more complex codec and its WASM build runs several times slower. The realtime and cpu-used flags reduce quality slightly to keep conversion times tolerable, but a long clip may still take a few minutes.
Why is the first conversion slower than subsequent ones?
FFmpeg.wasm is roughly 30 MB. It downloads on the first run of the session and is cached by the browser for later conversions, so subsequent runs skip the download step.
What input formats are supported?
MP4, MOV, WebM, MKV, and AVI are the most commonly tested inputs. FFmpeg can read many more formats, but support depends on the demuxers and decoders compiled into the WASM core build.