BrowserTools
Advertisement
Home / Video / Video Converter

Video Converter

Convert video between MP4, WebM, MOV, MKV, AVI and GIF locally in your browser.

Maintained by BrowserTools · Last updated 2026-06-21

Loading Video Converter… If nothing happens, please enable JavaScript.

A video converter changes a video file from one container and codec combination to another, for example turning a MOV recorded on a phone into a widely compatible MP4, or shrinking a clip into a WebM for the web. A video file has two layers that matter: the container (MP4, WebM, MOV, MKV, AVI), which is the wrapper that holds everything, and the codecs inside it (H.264, VP9, AAC, Opus), which are the algorithms that actually compress the picture and sound. Converting usually means re-encoding those streams, which is why it takes real computation rather than a simple rename.

Frequently asked questions

Is my video uploaded to a server?
No. The conversion runs entirely in your browser using a WebAssembly build of FFmpeg. Your file is read locally, processed on your device, and returned as a download. It is never sent over the network, so it is safe to use with private or confidential footage.
Which formats can I convert between?
You can convert to MP4 (H.264/AAC), WebM (VP9/Opus), MOV, MKV, AVI and animated GIF. The converter accepts most common input formats that FFmpeg can decode, including MP4, MOV, WebM, MKV, AVI, FLV, and more.
Why is conversion slower than a desktop app?
This tool uses the single-threaded WebAssembly build of FFmpeg so that it works without special cross-origin isolation headers (which would interfere with other parts of the site). Single-threaded encoding is slower than a native multi-core app. For short clips it is quick; for very large files a desktop tool will be faster.
Is there a file size limit?
There is no hard limit, but the whole file is held in browser memory during conversion, so very large videos (well over 1 GB) can exhaust available RAM and fail, especially on phones or low-memory machines. For best results convert clips up to a few hundred megabytes, or trim or compress first.
What is the difference between the container and the codec?
The container (MP4, WebM, MKV, etc.) is the wrapper file that holds the video and audio streams plus metadata. The codec (H.264, VP9, AAC, Opus) is the compression method used for each stream. A single container can hold different codecs, which is why two MP4 files can behave differently depending on what is inside them.
Which format should I choose?
Choose MP4 (H.264/AAC) for maximum compatibility across devices, browsers and social platforms. Choose WebM (VP9) for smaller files when embedding on a website. Use MOV for Apple workflows, MKV for archiving with multiple tracks, and AVI only when older software requires it.
Does converting reduce quality?
Re-encoding is lossy, so each conversion can lose a little detail, just like re-saving a JPEG. The converter uses sensible quality settings to keep the loss small and usually invisible. To minimise quality loss, avoid converting the same clip back and forth many times.
Does it work offline?
Yes, once the page and the converter engine have loaded. The first conversion downloads the FFmpeg core (about 30 MB), after which it is cached and the tool works without an internet connection until the cache is cleared.

About Video Converter

This converter runs entirely inside your browser using a WebAssembly build of FFmpeg, the same open-source engine that powers most desktop and server video tools. Your file is never uploaded: it is read from your device into the page, processed locally, and handed back as a download. That makes it safe for private recordings, unreleased footage, or anything confidential, because the video stays on your machine the whole time.

The most common reason to convert is compatibility. MP4 with H.264 video and AAC audio plays almost everywhere: phones, browsers, editors, social platforms. WebM with VP9 is smaller at the same quality and is ideal for embedding on a website. MOV is common from Apple devices, MKV is popular for archiving because it can hold many tracks, and AVI is an older format some legacy software still expects. Converting to the right target removes the dreaded codec not supported error.

Because everything happens on your own hardware with a single-threaded engine, conversion is slower than a native desktop app and very large files use a lot of memory. For short and medium clips it is fast and convenient; for multi-gigabyte files a desktop install of FFmpeg or HandBrake will be quicker. The first conversion also downloads the engine (around 30 MB), which is then cached for subsequent runs.

FFmpeg: the engine behind almost every video tool

Almost every video service you use, from streaming platforms to social apps to desktop editors, relies on FFmpeg somewhere in its pipeline. Started by Fabrice Bellard in 2000 and maintained by a large open-source community ever since, FFmpeg is a command-line powerhouse that can decode, encode, transcode, mux, demux, stream, filter and play virtually every audiovisual format ever created.

What makes this tool possible is FFmpeg compiled to WebAssembly. WebAssembly lets code originally written in C run inside the browser at near-native speed, which means the same engine that runs on servers can now run on the page you are reading, with your files never leaving your device. A few years ago, in-browser video conversion would have required uploading your file to a server farm; today it happens locally on your own hardware.

The trade-off is performance. The browser build used here is single-threaded so it stays compatible with ordinary web pages, whereas a desktop FFmpeg uses every CPU core. That is why a conversion that takes seconds on a laptop command line can take noticeably longer in the browser, the price of keeping your video completely private.

Related tools

Video Compressor

Compress and shrink video files locally in your browser, no upload, no quality wall.

Video to GIF Converter

Turn a video or clip into an animated GIF locally in your browser, with adjustable size and frame rate.
Advertisement
Advertisement
Advertisement