Compression · Knowledge
How Video Compression Works
A smaller MP4 is almost never a simple remux — compressors decode the source and encode again. That takes CPU time in the browser and can reduce quality if you push settings too far.
Quick take: Video compressors shrink files by re-encoding. Lower quality/bitrate = smaller MP4 and more risk of softness or artifacts.
Containers vs codecs
MP4, MOV, MKV, and WebM are containers. The codec (H.264, VP9, …) does the heavy compression. Delivery compressors usually target a widely compatible MP4 encode.
Quality / CRF-style controls
Sliders map to how hard the encoder works to keep detail. Lower settings favor size; higher settings keep more fidelity at larger sizes. Long 4K clips take longer locally than short phone videos.
Format Convertly video tools
The Video Compressor and format pages (MP4, MOV, WebM, MKV) force a re-encode for size — remux alone rarely shrinks much. Keep the camera or NLE master; compress a delivery copy.
Key points
- Shrinking video usually means re-encoding, not just renaming.
- Bitrate/quality settings dominate final size.
- Compress once from the best master for uploads.
Open a compressor
Shrink files privately in your browser — pick a category, then a format tool when you know the extension.
Re-encode common video containers to a smaller MP4 in your browser.
Related compression guides
Related quality guides
Related concepts
FAQ
Why is the first run slow?
The browser media engine loads once, then encodes locally. Short clips finish much faster than long high-resolution files.
Does MOV to a smaller MP4 keep quality?
Only if you keep quality high. Re-encoding can reduce quality — that is how size drops.
Browse all compression guides, compressors, or quality guides.