The quality presets select different starting bitrate targets. They are not promises of a particular percentage reduction because source codec, motion, duration, audio, and scene complexity all affect the final file.
Guide · Video compression
How to compress a video in your browser without uploading the source for compression.
FlyThe BG uses browser media capabilities to decode and encode supported videos locally. This guide explains what the quality controls actually do, why target size is best-effort, and when a phone or browser may reach its limits.
01 · Choose a target
Start with the result you actually need.
Quality, output resolution, and target size solve different problems. A smaller resolution can reduce both pixel workload and bitrate requirements, while quality changes the compression target at the selected resolution.
Reducing a 4K recording to 1080p can remove a large amount of pixel data. Keep the original resolution when detail matters more than file size.
A target such as 25 MB is used to calculate a starting video bitrate from duration. The final MP4 can still be above or below the target because encoding and container overhead are not perfectly predictable.
02 · What happens locally
The browser performs the media work.
The compressor uses supported browser decoding and encoding APIs rather than sending the selected video to a FlyThe BG compression endpoint.
The browser reads the source container and decodes video frames. Compatibility is feature-detected before a job begins where possible.
Supported browsers encode an H.264 video stream and package it into an MP4 output. Audio and container behaviour can affect the resulting size.
FlyThe BG reports the actual output size after encoding instead of pretending the requested target was achieved exactly.
The resulting file is exposed as a browser download. Your browser, operating system, extensions, and download folder can retain their own copies outside the page.
03 · Better compression choices
Use the smallest change that solves the problem.
For sharing a phone recording, reducing resolution is often more useful than aggressively lowering quality. For archive storage, preserve resolution and choose a moderate quality setting.
Try 1080p or 720p with Medium quality when the destination already recompresses uploads.
Reduce resolution first if the destination does not need the original pixel dimensions.
Leave headroom below the platform limit because an exact final size cannot be guaranteed by a target-size encoder.
Expect more CPU, memory, battery, and time. A browser tab can be suspended or the device can run out of resources on unusually large jobs.
Video compression FAQ
Know the limits before you start.
Does the compressor upload my video?
The compression workflow is designed to decode and encode the selected video in browser memory rather than sending it to a FlyThe BG compression endpoint. Other site features such as advertising or analytics can make separate requests, as described in the Privacy Policy.
Why is the final size not exactly my target?
The target is a bitrate calculation, not a container-level guarantee. Keyframes, motion complexity, audio, codec behaviour, metadata and MP4 overhead all affect the final byte count.
Why can compression take a long time?
Video encoding is CPU-intensive. Longer videos, higher resolutions and slower devices require more work, and browser scheduling can reduce throughput when the tab is backgrounded.
What if my browser is not supported?
FlyThe BG checks browser codec capabilities and can report that a local path is unavailable instead of pretending that a conversion will work.
Compress locally
Make a smaller MP4 and inspect the real output size.
Use the live browser compressor for supported videos.