Why does compression take a long time?

Video compression is computationally intensive. FFmpeg runs in a WebAssembly thread in your browser, which is slower than native desktop encoding. A 100MB video may take 1–5 minutes depending on your device. Two-pass mode (Target Size) takes twice as long.

What output format does the tool produce?

All output is MP4 with H.264 or VP9 video and AAC audio. MP4 plays on every device and browser without compatibility issues.

Is my video uploaded to a server?

No. Everything runs locally in your browser using WebAssembly (FFmpeg.wasm). Your video never leaves your device.

What is CRF and what number should I choose?

CRF (Constant Rate Factor) controls quality. Lower numbers mean better quality and larger files. CRF 18 is visually lossless, CRF 26 is the default balanced setting, and CRF 35 produces small files with noticeable quality reduction. For most sharing purposes, CRF 24–28 works well.

Images Tool Box

Compression

Video Compressor Online Free

Reduce video file size directly in your browser — no server upload, no software install. Choose Auto mode for quick results, or dial in CRF quality, target a specific file size in MB, or downscale resolution. Supports MP4, MOV, AVI, WebM, and MKV.