Video Compress
Reduce video file size with presets for web, email, social, and archive — or fine-tune with CRF control.
Key facts about Video Compress
| Two modes | quality-first here (CRF 15-40 and presets) and limit-first on the compress-video-for-Discord page, where a byte ceiling becomes a two-pass bitrate budget |
|---|---|
| Why CRF cannot promise a size | CRF holds quality constant and lets the bitrate follow the content — the same CRF 28 gives a few MB of a talking head and tens of MB of gameplay |
| Target-mode formula | target bytes x 8 / 1000 / duration, times 0.94 for container overhead, minus the audio bitrate; 10 MB over 15 s leaves 5,160 kbps of video |
| Codecs | MP4 and MOV use H.264 (libx264) with AAC; WebM uses VP8 (libvpx) with Opus |
| VP9 is never used | it is compiled into the pinned single-threaded ffmpeg core but fails at runtime on it, writing empty or header-only files |
| Where the work happens | ffmpeg compiled to WebAssembly, in a worker in this tab; the ~32 MB core is fetched once from the public jsDelivr CDN and then cached |
| Input ceiling | 200 MB — the whole clip lives in one WebAssembly heap during a re-encode |
What happens to your file
Your video is not uploaded. ffmpeg compiled to WebAssembly runs in a worker inside this tab and reads and writes an in-memory filesystem that only this page can see. The one thing that leaves the browser is the engine: on the first encode of a session the page fetches ffmpeg-core.js and a roughly 32 MB ffmpeg-core.wasm from cdn.jsdelivr.net/npm/@ffmpeg/core@0.12.10. That request contains no part of your file. After it is cached, encoding makes no network requests at all, and the result is a blob: URL discarded when the tab closes.
About this tool
- 1
Upload video
Select a video file (MP4, WebM, MOV, AVI, MKV).
- 2
Choose quality preset
Low = smallest file, Medium = balanced, High = best quality.
- 3
Compress
ffmpeg.wasm re-encodes the clip inside this tab — H.264 for MP4/MOV, VP8 for WebM. Nothing is uploaded.
- 4
Download
Save the compressed video and see the size reduction percentage.
- Medium quality typically reduces file size by 40-60% with minimal visible difference.
- Videos with static scenes (talking head, slides) compress much more than action footage.
- The CRF (Constant Rate Factor) value controls quality: lower = better quality, larger file.
- Always preview the compressed video before deleting the original.
- Quality presets
- Size comparison
- Percentage saved
- Progress tracking
- Multiple formats
- Reduce video size for email attachments.
- Optimize videos for web hosting and streaming.
- Compress screen recordings that are unnecessarily large.
- Prepare videos for messaging apps with size limits.
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