Video Compression takes large files from a phone, a camera or a screen recording down to a size that can be sent in WeChat, uploaded to cloud storage or attached to an email. It is the “Video compression” tab of the audio/video workbench and re-encodes with H.264 through ffmpeg in the browser; whatever the source container is (MOV, MKV or AVI), the output is always MP4 (H.264 + AAC), named <original-name>_compressed.mp4.

It shares the same encoder as Video Format Converter. The difference is that the three presets here bundle CRF (constant rate factor — the higher the number, the harder the compression and the worse the picture), a resolution cap and an audio bitrate: HD priority is CRF 21 at the original resolution with 128 kbps audio; Balanced is CRF 26 capped at 720p with 128 kbps audio; Extreme compression is CRF 31 capped at 480p with 96 kbps audio. Resolution is only ever reduced, never enlarged, so a 720p source under Balanced will not be stretched.

1. 01Add the file— drag a video into the audio/video workbench, select it in the file list on the left and switch to the “Video compression” tab. The panel below shows the original size and the detected overall bitrate for comparison.
2. 02Pick a tier— click “HD priority”, “Balanced” or “Extreme compression”; if none of them fits, click “Custom parameters…” and drag CRF yourself (18–34), choose a resolution cap (original / 1080p / 720p / 480p) and an encoding speed preset.
3. 03Check the estimated command— the panel shows the ffmpeg command that is about to run in real time, so you can copy it for your records or reproduce it on your own computer.
4. 04Start compressing— click “Start compression” and the job joins the queue at the bottom; when it finishes, click Download for <original-name>_compressed.mp4. Several videos can be submitted one after another and the queue processes them serially.

Output format

— fixed MP4 (H.264 yuv420p + AAC); the source container cannot be kept and WebM cannot be produced (use Video Format Converter for WebM)

Speed

— single-threaded ffmpeg in the browser runs at roughly 1/5–1/10 of native speed on a computer, so 10 minutes of 1080p may take a quarter of an hour; do not close the page while it runs

File size

— files over 1.5 GB get a warning that they may fail (the browser's memory ceiling is around 2 GB); split them with Video Splitter first and then compress

Unsupported sources

— video encoded with AV1 cannot be decoded in the current build and reports an error as soon as you start

What it does not do

— there is no “compress to a target size in MB” mode, only CRF and resolution can be tuned towards it; it does not crop the picture (use Video Crop) or drop audio tracks (use the mute mode of Volume Adjust)

The video is processed locally in the browser by ffmpeg.wasm and its contents are never uploaded to any server; the first use downloads about 31 MB of ffmpeg engine files from a CDN (the site's asset domain or jsDelivr), and that request does not include your file.