Kompresor Video — Darmowe narzędzie online

Free video compressor — reduce video file size in your browser

Narzędzieolis Video Compressor reduces video file sizes entirely in your browser using the MediaRecorder API. Choose quality and resolution settings, and the tool re-encodes your video at a lower bitrate. Nie uploads, no server processing, no account needed. Your video stays on your device throughout the entire process.

How browser-based video compression works

The compression process works in four stages. First, your video file is loaded into an HTML5 video element. Second, as the video plays, each frame is drawn to an off-screen Canvas at your target resolution. Third, the Canvas stream and the original audio track are combined and fed into the browser's MediaRecorder API, which re-encodes the content at a controlled bitrate. Fourth, the recorded chunks are assembled into a downloadable WebM file.

This approach leverages the hardware-accelerated video codecs built into your browser (VP8 or VP9 in Chrome/Firefox, H.264 in Safari), ensuring reasonable compression speed without any external dependencies or plugins.

Quality vs. file size trade-offs

• Low quality — Aggressively reduces bitrate. Best for archival, previews, or content where visual quality is not critical. Expect 70-90% file size reduction.
• Medium quality — Balanced compression suitable for web sharing, social media, and email attachments. Expect 40-60% file size reduction.
• High quality — Minimal quality loss. Best for footage you want to keep looking sharp. Expect 20-40% file size reduction.

Resolution impact on file size

Reducing resolution has the biggest impact on file size. A 1080p video downscaled to 720p contains 44% fewer pixels per frame, which translates to roughly proportional file size savings on top of bitrate reduction. For social media sharing (WhatsApp, Instagram DMs, Discord), 720p is usually more than sufficient. For professional use, keep the original resolution and focus on bitrate optimization.

Why WebM output?

The browser's MediaRecorder API natively supports VP8/VP9 encoding (which produces WebM files) in Chrome, Firefox, and Edge. MP4 encoding (H.264) is available in Safari but not yet widely supported in MediaRecorder across all browsers. WebM is supported for playback in all modern browsers, WhatsApp, Telegram, Discord, and most video platforms. If you specifically need MP4, the WebM output can be quickly converted using FFmpeg (ffmpeg -i input.webm output.mp4) or any online video converter.

Limitations to keep in mind

• Processing time — compression happens in near-real-time. A 10-minute video takes approximately 10 minutes to process.
• Browser memory — very large files (1 GB+) may exhaust browser memory. Close other tabs to free up resources.
• Audio quality — audio is re-encoded along with video. For audio-critical content, consider using dedicated audio tools.
• Codec support — older browsers may not support VP9. The tool falls back to VP8 automatically.

When to use desktop tools instead

For batch processing, H.264/H.265 output, fine-grained bitrate control, or videos longer than 30 minutes, desktop tools like HandBrake (free, open source) or FFmpeg (command line) are more appropriate. They offer hardware acceleration, two-pass encoding, and access to all major codecs. This browser-based tool is optimized for quick, single-file compressions where privacy and convenience are priorities.