Compress Video to Target Size

How is the bitrate calculated?

File size is just bitrate times duration, so to hit a size you solve for bitrate. Convert the target from megabytes to bits, divide by the length in seconds, and subtract the audio bitrate to leave the budget for the picture:

total_bitrate (bits/s) ≈ target_bytes × 8 / duration_seconds
video_bitrate ≈ total_bitrate − audio_bitrate

A worked example: to fit 25 MB for a 60-second clip, that is 25 × 1024 × 1024 × 8 ≈ 209,715,200 bits over 60 s ≈ 3,495 kbps total. Take off a 128 kbps audio track and the video gets about 3,367 kbps. The tool then trims a few percent of headroom off that, because container overhead and encoder variance can nudge the file over an exact ceiling. Naming the audio bitrate matters: at 60 seconds every 32 kbps of audio you drop hands roughly another 240 KB back to the video.

What are the common size limits?

The classic reason to do this is “keep it under 25 MB for email”, but every platform has its own ceiling. These change over time and by plan, so treat them as a starting point rather than gospel — check the current limit if you are close to the edge.

If the math forces the bitrate so low that the picture falls apart, you have three honest choices: shorten the clip with trim video, lower the resolution with resize video, or — when the visuals do not matter — drop the video entirely and send just the extracted audio as an MP3, which is a fraction of the size.

What are the browser limits here?

Two passes of single-threaded WebAssembly encoding is roughly double the work of an ordinary compress, so this is the slowest tool in the set on long clips, and very large inputs can exhaust the tab’s memory. It shines on the short clips people actually need to squeeze under a limit — a screen recording, a phone clip, a highlight. For a feature-length file, a desktop encoder is the better tool.

Does my video get uploaded?

No. The size calculation and the encode both run locally through ffmpeg.wasm; your file never leaves the tab. Verify it in DevTools → Network — no upload request appears while it works, and it keeps working offline once loaded. Confidential footage stays on your machine.

Related video tools

If you do not need an exact number, the quality-slider compress video is simpler. Pair this with resize when the bitrate would otherwise be too low, or trim to cut the duration in the formula. When it fits, add subtitles before you send it.