Compress an MP4
Drop in an MP4, pick a quality level, get a smaller file. No upload.
drop a video here
or click to choose
How MP4 compression works
An MP4 file is just a container holding an H.264 (or H.265) video stream and an audio stream. To make it smaller, we re-encode the video at a different quality level — higher CRF means more compression and smaller file size, with a slight tradeoff in visual quality.
How small can I make it?
- From 100% to ~50% — no visible quality change. CRF 23 (default).
- To ~25-30% — minor softness on detail. CRF 26-28.
- To ~10-15% — clearly compressed, but still watchable. CRF 30-32.
- Below 10% — visibly artifacted. Only use for previews.
Also shrinks resolution if you want
Downscaling from 4K to 1080p, or 1080p to 720p, also massively reduces file size. Combine resolution downscaling with a higher CRF for the smallest possible file.
FAQ
What's CRF?
Constant Rate Factor. It's an H.264 quality dial: 0 = lossless, 23 = default, 51 = worst possible. Each +6 roughly halves the bitrate.
Will it work for HEVC / H.265 MP4s?
The input can be HEVC; we decode whatever's in there. The output is always H.264 (libx264), which is more universal.
Does the file get uploaded anywhere?
No. Nothing is uploaded. Open your browser's network tab while you convert and you will see your file never leaves the page. Once the converter itself has downloaded, it keeps working on this device even with no connection.
What's the maximum file size?
Browser memory is the limit. WebAssembly caps at 2–4 GB per file. Most laptops handle 1080p videos under a gigabyte comfortably.
Why is it slow on my phone?
FFmpeg-WASM runs on your CPU, not hardware video encoders. Phones have less CPU, so encoding takes longer.
Can I cancel mid-encode?
Yes. The Cancel button terminates the worker immediately. You'll wait a few seconds the next time you start.