A big video file is easy to make and hard to share. The good news: most footage can shrink a lot before you notice any drop in quality, because modern encoders throw away data your eyes barely register. This guide explains what actually controls quality, then shows how to compress a clip in your browser with Supercut, where the footage never leaves your device.
Three things drive file size: resolution (the pixel dimensions), bitrate (how much data each second of video gets), and the codec doing the encoding. Most of the quality loss people complain about comes from a heavy-handed bitrate cut, not from compression itself. A smarter approach is constant-quality encoding (CRF, in H.264 terms), where the encoder spends bits where the picture needs them and saves bits on flat or still areas. You keep detail in the parts you look at while still cutting the overall size. Resolution matters just as much. A 4K phone clip watched on a phone or in a feed has far more pixels than the screen will ever show. Downscaling 4K to 1080p, or 1080p to 720p, can shrink the file substantially with no visible loss for social or messaging, because you are throwing away pixels nobody was going to see.
Start with the codec. H.264 (MP4) is the safe, universal choice and plays everywhere. Newer codecs can squeeze harder, but H.264 is the best balance of size, quality, and compatibility for anything you plan to send to other people. Keep audio sensible too: around 128 kbps is plenty for most speech and music, and going lower saves little while being easy to hear. Then match the output to where it is going. For email or chat, downscale to 1080p or 720p and let constant-quality encoding handle the rest. For a platform like TikTok or YouTube, export close to its native size so the platform does not re-compress an already-compressed file a second time. The single habit that hurts quality most is compressing the same clip over and over, so do it once, from the highest-quality source you have.
Supercut compresses video entirely on your device using FFmpeg compiled to WebAssembly. Your footage never gets uploaded. Only the text of your prompt is sent, so the AI knows what edit to plan, then a deterministic engine maps that to the right encoding settings and runs them locally in your browser. There is no upload step, so a large 4K file starts processing right away instead of crawling through your connection. Once the page has loaded, the work even keeps running if your connection drops mid-edit. You type what you want in plain English, watch the result in the preview, and download. Nothing to learn, and no copy of your file sitting on someone else's server.
Open the editor and drag your video into the browser. It loads locally on your device. No upload, and no account needed to try your first export.
Say what you want, like "compress this video to a smaller size" or "compress and downscale to 720p for email." Supercut plans the edit and picks encoding settings that cut size while keeping the clip watchable.
Watch the compressed clip in the preview and confirm it still looks sharp. Want it smaller? Ask for a lower resolution. Want more detail back? Ask to keep it at the source size.
Export the smaller file and save it. The whole process ran in your browser, so the original footage never left your device.
Compress video to a smaller file size in your browser. Shrink clips for sharing without uploading them anywhere, your footage stays on your device.
Change video resolution and dimensions in your browser. Downscale for smaller files or match platform sizes, your footage never uploads.
Convert MOV, WebM, or other formats to MP4 in your browser. Universal playback without uploading your source file.
Trim highlights, reframe to vertical, caption, and compress for Discord, in your browser. Big gameplay files are handled on your device, no upload.
Crop, resize, and compress product videos for Shopify, Amazon, and TikTok Shop, in your browser. Unreleased product footage stays on your device.
Not literally zero, but you can get very close. Constant-quality encoding and a sensible resolution let you cut file size a lot while keeping the picture sharp enough that most viewers see no difference. The visible loss usually comes from over-aggressive bitrate cuts or from compressing the same clip several times.
No. Compression runs in your browser with WebAssembly, so the file never leaves your device. Only your text prompt is sent, so the AI can plan the edit.
It depends on the clip and how much quality you want to keep. Lowering the resolution and using constant-quality encoding can cut size dramatically. You preview the result and can ask for smaller or higher quality before you export.
MP4 with H.264 is the best default. It plays on virtually every device and platform and balances small size with good quality. Supercut can also convert between common formats if you need something else.
You can try your first export free with no account. After that, a paid plan unlocks unlimited watermark-free exports and every tool, starting at 4.99 a month billed yearly, with monthly and one-time lifetime options. You can cancel anytime.