ConvertBox Logo
ConvertBox

Compress Video

Reduce MP4, MOV, AVI, and WebM video file sizes online for free. Adjust compression quality and compress video directly in your browser — no upload needed.

How to Use

  1. Select the video file to compress
  2. Set the desired quality
  3. Click "Compress Video" button
  4. The compressed video will be downloaded automatically
  5. Verify the output file in your device's download folder.
  6. You can adjust settings and process new files immediately without any restrictions.

All processing is done in your browser, and files are never sent to a server.

Frequently Asked Questions

CRF (Constant Rate Factor) controls video quality. Lower values mean higher quality but larger files. Values between 23-28 are recommended for most uses.
Depending on the CRF setting, you can achieve 30-80% file size reduction.
No, compression reduces file size by adjusting quality parameters, not resolution.
If compression fails: (1) use a file under 500MB, (2) try a lower quality setting (higher CRF = faster processing), (3) convert to MP4 first, (4) refresh the page and retry.
No. All operations are processed entirely inside your browser's local sandbox using client-side APIs (like WebAssembly, pdf-lib, or HTML5 Canvas). Your files and data never leave your device.
The tool is completely free with no usage limits. However, since processing occurs in your browser's memory, we recommend keeping file sizes under 50MB (especially for heavy files like PDFs or videos) to ensure stability.
No. All tools on ConvertBox are 100% free. We do not insert watermarks, limit features, or require any registration or payment.
Yes. Once the page and its local library dependencies are loaded in your browser, the conversion logic runs completely offline without needing an active internet connection.

Related tools

Convert Video

Convert video files online in your browser. Convert MP4, MOV, WebM, AVI, and MKV formats locally via FFmpeg.wasm. Free, secure, and no watermark.

MP4MOVWebM
Get Started

Trim Video

Trim and cut MP4, MOV, and other video files to any segment online for free. Set precise start and end times, preview in browser, and download instantly.

MP4MOVWebM
Get Started

Video → GIF

Convert video clips into animated GIFs in the browser with trimming, size, and frame-rate controls, keeping source files on your device.

MP4 → GIF
Get Started
NEW

Screen Recorder

Record your screen, tab, or webcam directly in the browser. Save as WebM or convert to MP4, capture audio, no installation or signup required.

Get Started

Extract Audio

Extract audio from MP4, MOV, AVI, and other video files for free. Save as MP3. No upload needed — all processing happens locally in your browser.

Video → MP3
Get Started
NEW

Add Subtitle

Burn SRT/VTT subtitles into your video or embed them as a soft track. Runs entirely in your browser — files never leave your device.

SRTVTT
Get Started