Set the size you have to hit — 16 MB for WhatsApp, 25 MB for email — and the settings work backwards to reach it. Your file is never uploaded.
Most people arrive at a compressor with a specific number in mind: WhatsApp refuses anything over 16 MB, most email servers stop at 25 MB, and some forms cap lower still. So this tool works from that number backwards rather than offering vague quality presets.
Three levers do almost all the work, in this order: trimming, resolution, and audio. Cutting a clip in half halves the file. Dropping 1080p to 720p removes more than half the pixels. Removing audio saves roughly a megabyte a minute. The live estimate updates as you touch any of them, so you can see which one is actually buying you space.
One honest caveat: if your source is already a well-compressed H.264 file at a low bitrate, re-encoding can produce something larger. The tool detects that and tells you instead of pretending it succeeded.
The estimate assumes a steady bitrate. Busy footage with a lot of motion overshoots slightly and a static talking head usually lands under. Aim a couple of megabytes below a hard limit.
Some loss is unavoidable, but most of the visible damage comes from squeezing a large frame too hard. Dropping the resolution first usually looks better than keeping 1080p at a very low bitrate.
The browser re-encodes frames as it plays them, so processing runs at real time. Trimming first is the fastest way to cut both the wait and the size.