Convert video to MP4 or WebM
Turn iPhone MOV files, MKV downloads or AVI archives into MP4 that plays everywhere, or WebM for the open web. Choose a quality level and optional maximum width. Conversion runs on your device.
How to use the Video Converter
- Drop a video in any common format.
- Choose MP4 (recommended) or WebM.
- Optionally cap the width to reduce size.
- Click Convert and download.
Containers and codecs
A video file is a container (MP4, MOV, MKV, AVI, WebM) holding a video stream (H.264, HEVC, VP9, AV1…) and an audio stream (AAC, MP3, Opus…). Playback problems usually come from the codec, not the container: an MP4 with HEVC video will not play in many browsers or on Windows without an extension, while an MP4 with H.264 plays on practically everything made since 2008. This tool always re-encodes to H.264 + AAC for MP4, which is why the output is universally playable.
iPhone MOV and HEVC
iPhones record MOV files with HEVC (H.265) by default. Converting to H.264 MP4 makes them play on Windows, Android, older TVs and in web pages, at roughly 1.5–2× the file size for the same quality, or the same size at a slightly lower quality setting. If you only need Apple-to-Apple sharing, no conversion is needed.
MP4 or WebM?
MP4/H.264 is the safe choice for sharing and for any device. WebM (VP8 here, for speed) is royalty-free and well supported by browsers, useful for HTML5 video where you want an open format alongside MP4. Encoding VP8 in the browser is slower than H.264.
How it runs without uploading
This tool uses ffmpeg, the same open-source engine behind most video software, compiled to WebAssembly. The first time you use a video tool the engine (about 30 MB) is downloaded from a content delivery network and cached by your browser; after that it loads instantly, even offline. Your video is read into memory, processed by the engine inside the browser sandbox, and the result is offered as a download. Nothing is transmitted. Because it runs on one CPU core, encoding takes roughly real time to three times real time depending on your device: a 30-second clip takes 30–90 seconds, a 10-minute video may take 10–30 minutes and needs a few hundred megabytes of free memory. For long videos, trim first or use a desktop tool.
Frequently asked questions
Why is the MP4 bigger than my MOV?
The MOV probably used HEVC, which is more efficient. H.264 needs more bits for the same quality; raise the CRF value or cap the width to compensate.
Does it convert 4K?
Yes, but encoding 4K in the browser is slow; cap the width at 1920 unless you need 4K output.
Is the file uploaded?
No. Conversion runs in your browser.
Privacy
This tool runs entirely inside your browser using WebAssembly and the Canvas/File APIs. Your files are never uploaded to ToolFlint or any third party; you can verify this in your browser's network tab or by switching to airplane mode after the page loads. Read how we process files.
Last updated 2026-09-23.