MP4 Converter
FFmpeg Online — Run FFmpegin Your Browser
Turn MOV, MKV, WebM and other videos into MP4, or an MP4 into MP3, GIF and more, right in your browser. Nothing is uploaded.
Convert, compress, trim, and process video & audio locally. Files never leave your device. No signup. The real FFmpeg.- 100% private — nothing is uploaded
- Free, no account
- Real FFmpeg — any command runs
MP4 Converter — tool
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What this does
Turn MOV, MKV, WebM and other videos into MP4, or an MP4 into MP3, GIF and more, right in your browser. Nothing is uploaded. It runs the real FFmpeg, compiled to WebAssembly, right inside your browser — nothing is installed, no account is needed, and your files are never uploaded to a server.
The FFmpeg command
This is the exact command the tool runs for you. Copy it to run the same conversion with FFmpeg on your own machine.
ffmpeg -i input.mov -c:v libx264 -preset veryfast -pix_fmt yuv420p -movflags +faststart -crf 23 -c:a aac -b:a 128k output.mp4Convert any video to MP4
Add a video in almost any format (MOV from an iPhone, MKV, WebM, AVI, WMV, MPEG, TS, M4V, 3GP or FLV) and get an MP4 that plays on Windows, Mac, Android, iPhone, every browser and every social site.
The MP4 uses H.264 video and AAC audio, the most widely supported combination, set to the yuv420p pixel format so it doesn't show up green in some players.
Instant when possible
Many MOV, MKV and M4V files already hold video and audio that MP4 supports (H.264 video with AAC or MP3 audio). When the tool detects that, it offers to repackage the file into an MP4 without re-encoding: near-instant, at full original quality.
Otherwise it re-encodes the video. That runs in your browser, so a long video takes a while; the progress bar shows how far along it is.
Converting an MP4 to another format
Already have an MP4? Choose another conversion in the tool, or open one of the MP4 conversions listed on this page: MP4 to MP3, GIF, WAV, M4A, WebM, MOV or WebP.
Choosing the quality
When re-encoding, the Quality (CRF) slider trades size for quality. Lower numbers mean better quality and bigger files: 18 looks practically identical to the original, 23 (the default) is a good balance, and 28 to 30 gives much smaller files that look softer.
Same commands. No limits.
Test in your browser free — run at scale on Rendi's FFmpeg API. n8n, Zapier & Make integrations.
Frequently asked
Which videos can I convert to MP4?
Most common formats: MOV, MKV, WebM, AVI, WMV, MPEG, TS, M4V, 3GP, FLV and more. It's the real FFmpeg running in your browser, so it reads the same files the FFmpeg command line does. For an animated GIF, use the GIF to MP4 converter on this site.
Can I convert an MP4 to MP3 or GIF?
Yes. Choose that conversion in the tool, or open MP4 to MP3 or MP4 to GIF from the list on this page. Both run in your browser like everything else here.
Will converting to MP4 lose quality?
Not when the tool can repackage the file: the video and audio are copied as they are. When it has to re-encode, the default setting looks very close to the original; move the Quality slider to 18 if you want it practically identical.
How long does the conversion take?
Repackaging takes seconds even for large files. Re-encoding is slower in a browser than in a desktop app, so a long, high-resolution video can take several minutes.
Is this MP4 converter free?
Yes. There is no account, no sign-up and no limit on how many files you convert. Nothing is installed either: it runs in your browser.
Is it really private?
Yes. FFmpeg runs entirely in your browser via WebAssembly. Your files are never uploaded, streamed, or seen by any server — including ours.
What's the file size limit?
Around 2 GB, and it's a browser limit rather than ours. WebAssembly can only address so much memory, so the whole job has to fit in the tab. Lightweight operations that copy streams instead of re-encoding (trimming, remuxing, stripping the audio track) work on files right up near that ceiling, because the file is read in place instead of being copied into memory. Full re-encodes need room for the input, the output, and working memory at once, so their practical ceiling is lower — lower still on phones. For anything bigger, the exact same command runs with no size limit on the Rendi API.
Does it work on my phone?
Yes. It's a web page, so it opens in Safari or Chrome on a phone the same way it does on a laptop: nothing to install, and your files still never leave the device. The layout is built for touch, and the Run button stays pinned to the bottom of the screen while you work. What changes on a phone is memory — there's much less of it, so the size limits are halved: the tool stops at files over about 1 GB, and it refuses re-encodes over 500 MB instead of letting the tab crash mid-run. Trimming, remuxing and extracting audio stay cheap, so those are the jobs a phone handles best. For a long video or a heavy encode, send the same command to the Rendi API; that works from a phone just as well.
Why does my MP4 look green in some players?
That's a pixel-format mismatch. When a video isn't encoded as yuv420p, some players and browsers can't display it and fall back to green or garbled frames. Every MP4 our tools re-encode already sets -pix_fmt yuv420p, so you won't hit this here — and operations that copy the video stream untouched keep whatever format already played. If you write your own command in the terminal, add -pix_fmt yuv420p and it'll play everywhere.