Compress a Video to an Exact File Size
Channels enforce hard size limits: WeChat chat, email attachments, upload portals. Target-size compression solves "fit under the cap with the least quality loss".
Set the target from the receiving end
The target is decided by the receiver, not by greed: compress to 25 MB for WeChat chat (past that WeChat re-compresses anyway — better you control it), and leave ~5% headroom below platform caps.
Aim far below the cap and you pay quality for nothing.
How target-size encoding works
File size ≈ bitrate × duration. Given a target and duration, the encoder derives the average bitrate. Two-pass encoding scans the whole file first, then spends bits where the picture needs them — more consistent than single-pass at the same cost of roughly double the time.
When the target is too aggressive
Past ~10× reduction the math no longer favors quality. Two honest levers remain: drop resolution (1080p → 720p halves the information), or cut dead footage first — a 30-second trim beats a whole-file re-compression.