Is my video uploaded to a server?

No. ffmpeg.wasm runs entirely inside your browser using WebAssembly. Your video is never transmitted anywhere — it stays on your device throughout the entire compression process.

What is CRF and what value should I use?

CRF (Constant Rate Factor) controls the quality-to-file-size trade-off for H.264 encoding. CRF 18 is visually lossless; CRF 23 is high quality; CRF 28 is a good balance for sharing online; CRF 35+ produces very small files with noticeable quality loss. Start at 28 and adjust.

Does it work on iPhone and Android?

Yes. The tool works in Safari on iPhone and Chrome on Android without installing any app. The first run downloads the ~25 MB ffmpeg.wasm binary, which is then cached for future visits.

How much will my video file size be reduced?

Results vary by content. CRF 28 typically reduces file size by 30–60% compared to a high-bitrate original. Videos with lots of movement compress less than static scenes. Combining CRF 28 with a 720p downscale can cut file size by 70–80%.

Why is video compression slower than muting or trimming?

Compression re-encodes every single frame, which is CPU-intensive. Muting and trimming use copy-stream mode and finish in seconds. Expect roughly 1–3 minutes per minute of video on a modern laptop.

Video Compressor Online Free

Reduce video file size in your browser with ffmpeg.wasm — no upload, no watermark, no file size cap. Adjust CRF quality and optionally downscale resolution.

100% client-side · no upload

Video file (MP4, WebM, MOV, AVI, MKV…)

Settings Quality (CRF) — 18 = best quality, 40 = smallest file Max resolution (downscale only)

Load a file to begin.

How to use

Select your video file. MP4, WebM, MOV, AVI, and MKV are all accepted.
Set the CRF value — 28 is a good starting point. Lower (18–23) = higher quality, larger file. Higher (30–35) = smaller file for social sharing.
Optionally choose a max resolution to downscale (e.g. 720p for mobile uploads). Click Compress video and download the compressed MP4.

Related tools

More ways to use this tool

常见问题

Is my video uploaded to a server?: No. ffmpeg.wasm runs entirely inside your browser using WebAssembly. Your video is never transmitted anywhere — it stays on your device throughout the entire compression process.
What is CRF and what value should I use?: CRF (Constant Rate Factor) controls the quality-to-file-size trade-off for H.264 encoding. CRF 18 is visually lossless; CRF 23 is high quality; CRF 28 is a good balance for sharing online; CRF 35+ produces very small files with noticeable quality loss. Start at 28 and adjust.
Does it work on iPhone and Android?: Yes. The tool works in Safari on iPhone and Chrome on Android without installing any app. The first run downloads the ~25 MB ffmpeg.wasm binary, which is then cached for future visits.
How much will my video file size be reduced?: Results vary by content. CRF 28 typically reduces file size by 30–60% compared to a high-bitrate original. Videos with lots of movement compress less than static scenes. Combining CRF 28 with a 720p downscale can cut file size by 70–80%.
Why is video compression slower than muting or trimming?: Compression re-encodes every single frame, which is CPU-intensive. Muting and trimming use copy-stream mode and finish in seconds. Expect roughly 1–3 minutes per minute of video on a modern laptop.

Last updated: 2026-05-20 By jarvisbox