About Compress Video
AntiUpload's Video Compressor reduces the file size of any video without uploading it anywhere. It's the flagship in the video toolkit because compression is the highest-volume request: people record 1080p phone clips that are 100+ MB and then can't email them, share them on Discord's free tier (25 MB cap), or fit them under WhatsApp's 16 MB global limit. We use libx264 in WebAssembly with CRF (Constant Rate Factor) quality presets — same encoder Handbrake desktop uses, same quality settings the professional FFmpeg tutorials recommend, just running inside your browser instead of on a server.
Four CRF presets cover the dominant tradeoffs: Best (CRF 20, near-visually-lossless, ~40% size reduction on typical phone clips), Balanced (CRF 23, the libx264 default — works for 90% of users, ~60% size reduction), Smaller (CRF 28, noticeable but acceptable compression artifacts, ~75% reduction), and Smallest (CRF 32, obvious artifacts but the smallest file). Pair with optional resolution downscale (1080p / 720p / 480p / 360p) for compounding size savings — a 4K source compressed to Balanced + downscaled to 720p is typically 90%+ smaller than the original.
Cloud video compressors (Veed, FreeConvert, CloudConvert, VideoSmaller, Clideo) all charge for the big-file case: free tiers are 100-500 MB max, watermarked, queued, or paywalled. The economics make sense for them — server CPU isn't free. For us they don't apply: the entire encode runs on your CPU/GPU. On Chromium / Safari 17+ the upcoming WebCodecs path will route encoding through your device's hardware H.264 encoder for 5-20× speedup; for now we use FFmpeg WASM libx264 with the `ultrafast` preset and `medium` effort level as a quality-vs-speed compromise tuned for the WASM build's lack of x86 ASM acceleration.
How it works
- Drop your videoAccepts MP4, MOV, WebM, MKV, AVI, M4V, FLV. No file-size limit from us — multi-gigabyte 4K recordings work fine. The constraint is your device's available RAM.
- Pick a quality presetBest (CRF 20) preserves detail aggressively, modest savings. Balanced (CRF 23, default) — the libx264 standard, fine for 90% of uses. Smaller (CRF 28) is the sweet spot when fitting platform caps. Smallest (CRF 32) for last-resort space savings.
- Optionally downscale resolutionResolution downscale compounds with CRF for bigger savings. A 4K source at Balanced + 1080p downscale typically shrinks 70-85%. 720p downscale produces ~90% savings on 4K source.
- Optionally pick encoder effortMedium effort (default) is bench-tuned — produces smaller files at the same CRF target compared to ultrafast, at 1.4× encode time. For long clips on slow devices, switch to ultrafast and accept slightly larger output.
- Click Compress videoOutput is always MP4 (universally playable). Progress bar shows live frame= updates so you can confirm encoding is alive. Result panel shows the % size reduction.