MP4 Compressor
Reduce MP4 video file size in your browser. Higher CRF = smaller file with more compression.
Drop or click to select (mp4, m4v)
First run downloads ~30MB ffmpeg engine; subsequent runs are instant. Everything stays in your browser.
About this tool
MP4 is the most compatible video container on the web — it plays in every browser, every phone, and every video editor. Most MP4s use H.264 video, which compresses well but can still produce huge files for long clips or high resolutions. This MP4 Compressor uses the in-browser build of ffmpeg to re-encode H.264 video at a lower bitrate, shrinking the file without changing the format.
Compression happens locally in your browser through WebAssembly. Your clip is never uploaded, which is important for confidential footage, internal training videos, and personal memories alike. You can either pick a CRF (Constant Rate Factor) for quality-targeted compression or specify an exact target MB to hit upload caps.
For very long or 4K source clips, expect compression to take several minutes — your CPU is doing real video encoding work, not a server's.
Why use it
- 100% in-browser — no upload, no server, no signup.
- Powered by ffmpeg.wasm — the same engine pros use.
- Set a target file size in MB to hit upload limits exactly.
- Free with no watermark.
How to use it
- 1Drop an MP4 or M4V file
Drag the clip into the upload box. Files of any length are supported, limited only by your device's RAM.
- 2Choose CRF or target size
CRF 23 is the visually neutral default. Lower CRF = higher quality and bigger file. Or enable target size and enter the exact MB you need.
- 3Wait for the encode and download
A progress bar shows you the percentage complete. When it finishes, download the new MP4.
Common use cases
- Sending video clips through email or messaging apps with size limits.
- Uploading lecture recordings to learning platforms with caps.
- Reducing screen recordings before sharing with clients.
- Saving cloud storage space on a phone camera roll.
- Compressing drone or GoPro footage for sharing.
- Preparing clips for social media that re-compress aggressively.
Tips for best results
The ffmpeg engine (~30 MB) downloads and caches the first time you use it. After that it stays ready for instant runs.
Dropping a 4K clip to 1080p often halves the file before you even touch the bitrate.
If only the first 30 seconds matter, cutting the rest of the clip is the cheapest way to shrink the file.
Frequently asked questions
How does CRF work?
CRF (Constant Rate Factor) controls quality vs size. 18 is visually lossless, 23 is a sensible default, 28 is small with light artifacts.
Why is the first run slow?
We download the ffmpeg engine (~30 MB) the first time. After that it's cached.