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Video Compressor

Your videos never leave your device

How to Compress a Video Online

  1. 1

    Select your video

    Click the upload area or drag and drop your video file. MP4, WebM, MOV, AVI, and MKV are all supported.

  2. 2

    Choose a quality level

    Use the quality slider to balance file size against visual quality. The default setting of 70% works well for most videos shared online.

  3. 3

    Click "Compress Video"

    Processing runs in your browser using WebAssembly. A progress bar shows you how far along it is. No upload needed — everything stays on your device.

  4. 4

    Download your compressed video

    Once finished, you'll see the original and compressed file sizes with the percentage reduction. Preview the result, then download the compressed MP4.

Understanding Video Compression

Video compression works by removing data that the human eye is unlikely to notice. Modern codecs like H.264 (the codec this tool uses) analyse each frame and store only the differences between frames rather than every pixel from scratch — a technique called inter-frame prediction.

The quality slider controls the Constant Rate Factor (CRF) — a parameter that tells the encoder how aggressively to compress. Lower quality means a higher CRF value, which discards more detail to achieve smaller file sizes. Higher quality means a lower CRF, preserving more detail at the cost of a larger file.

The CRF scale used here runs from 18 (near-lossless, quality 100%) to 35 (heavy compression, quality 0%). For most web-shared content, a CRF of 23–28 (quality 60–80%) produces results indistinguishable from the original at a fraction of the file size.

Frequently Asked Questions

Is my video uploaded to a server?
No. ClipIV runs entirely in your browser using WebAssembly technology. Your video file never leaves your device — no upload, no server processing, no storage. Everything happens locally.
How much can I compress a video?
It depends on the source material and the quality setting you choose. Typical reductions range from 30% to 80%. Videos encoded at high bitrates see the most dramatic savings. Moving the slider towards "Smallest file" increases compression — experiment to find the right balance for your needs.
Will the video quality be affected?
Yes — compression always involves a trade-off between file size and visual quality. The quality slider lets you control this balance. At 70% (the default) most viewers will not notice any difference for web playback. For archival purposes or professional use, consider keeping quality at 85% or above.
What formats are supported?
You can upload MP4, WebM, MOV, AVI, and MKV files. The compressed output is always an MP4 (H.264 video + AAC audio), which has the widest compatibility across devices and browsers.
Is there a file size limit?
There is no hard server limit because your file never leaves your device. Very large files (2 GB+) may be slow to process depending on your computer's CPU. We recommend compressing files under 1 GB for the best experience.