Why 4K files get so large so fast
A phone or camera shooting 4K at a high bitrate can produce several gigabytes for just a few minutes of footage. If the video is headed to a phone screen, a group chat, or a social platform that re-compresses it anyway, most of that original bitrate never actually improves what the viewer sees.
Hardware encoding, not just smaller settings
Apple Silicon Macs include a dedicated video encode/decode engine (part of the VideoToolbox framework) built specifically for formats like H.264 and HEVC. QuickCompress uses this hardware path rather than software-only encoding, so a large 4K file compresses in seconds instead of the many minutes a CPU-only re-encode would take, without draining the battery on a MacBook.
Resolution vs. file size
QuickCompress's "smaller" preset reduces file size while keeping your original resolution and format, which is usually the better trade-off for footage you'll still want to look sharp later. If the destination has a hard size ceiling instead, like an email attachment or a chat app's upload limit, target-size mode lets you specify the exact number instead of guessing.
Related
For general questions about the app, see video compressor for Mac. To hit a specific size for sharing, see compress video for email or compress video for Discord.