Video compressor

Open a video and this tool encodes several smaller versions of it entirely in your browser, using FFmpeg compiled to WebAssembly. Nothing is uploaded anywhere. Every version is an H.264 + AAC .mp4 with settings chosen to play in as many mobile browsers and operating systems as possible. Compare them side by side and download the smallest one that still looks good.

Filename

Versions to generate

	Name	Output size	Quality (CRF)	Audio

Add a custom version

Short side px CRF Audio kbps

Encoder speed H.264 profile Limit to 30 fps Strip metadata (location, camera, dates) No audio (drop the sound track) Only encode the first seconds (quick comparison)

Embed on a web page

Upload the video and the poster JPEG alongside your page, then paste this in. It uses the first video shown in the results above. preload="none" means the browser only shows the poster image and does not download any of the video until someone presses play.

XHTML

How the output files are made compatible:

H.264 video (libx264) in the Main profile by default, 8-bit 4:2:0 colour (yuv420p), even width and height, capped at 1080p and 60 fps. The H.264 level is picked automatically from the resolution and frame rate.
AAC-LC audio at 44.1 or 48 kHz, downmixed to stereo when the source has more channels.
MP4 container with the index moved to the front (+faststart) so playback can begin before the file has fully downloaded.
Only the first video and first audio track are kept. Rotation metadata from phones is baked into the pixels so every player shows the video the right way up.

Encoding runs on a single CPU core inside WebAssembly, so it is much slower than a native ffmpeg. Long or high resolution videos can take a while: use the "first N seconds" option to compare settings quickly, then encode the full version of the one you like. The ffmpeg engine (about 32 MB) is downloaded once and cached by your browser.

Video compressor

Versions to generate

Results, smallest first

Poster frame

Embed on a web page