How BoltCompress Compresses Your Video
No marketing, just what actually happens to your file, from upload to deletion.
1. Upload
When you pick a video, your browser asks our server for a one-time upload link and then sends the file directly to private cloud storage (Cloudflare R2) over HTTPS. Files get a random name, so they cannot be guessed. The limit is 250 MB per file and 5 videos per day.
2. Queue
Our server creates a job and places it in a queue. A separate worker machine picks it up, downloads the file from storage, and runs FFmpeg, the open-source video tool used by much of the industry. Your browser checks the progress every second.
3. Compression settings
First the worker reads your video's current bitrate with ffprobe. Then it sets a new target bitrate as a share of the original. That is why the tool can show an estimated size before you start, and why the output is always smaller than the input. Resolution and frame rate are not changed.
| Level | Video bitrate vs original | Codec | Preset | Best for |
|---|---|---|---|---|
| Fast & Light | About 75% | H.264 (libx264) | Default | Quality first, plays everywhere |
| High Efficiency | About 45% | H.265 (libx265) | Default | Everyday sharing, about half the size |
| Maximum Savings | About 25% | H.265 (libx265) | slow | Tight limits; busy scenes lose some detail |
The target never goes below 300 kbps, so very small originals may shrink less than the percentages suggest. All output uses the yuv420p pixel format for maximum compatibility. H.265 files in MP4 and MOV are tagged hvc1 so they play on iPhone, Mac, and Safari. MP4 and MOV files are also written with the index at the start (faststart), so they can begin playing before they finish downloading.
4. Output format
Some containers do not work well with every codec, so the format you choose can override the level's codec:
| Format | Video codec | Audio |
|---|---|---|
| MP4 | As per level (H.264 or H.265) | AAC 128 kbps |
| MOV | As per level (H.264 or H.265) | AAC 128 kbps |
| MKV | As per level (H.264 or H.265) | AAC 128 kbps |
| WebM | Always VP9 | Opus 128 kbps |
| AVI | Always H.264 | MP3 128 kbps |
Only the first video and the first audio track are kept. Subtitles and extra audio tracks are dropped.
5. Download and deletion
When the job finishes, the compressed file is uploaded back to storage and you get a private download link that expires after one hour (signed-in users can generate a fresh one from their recent videos). Uploaded and compressed files are deleted automatically after 24 hours by a storage lifecycle rule. We do not look at, analyze, or keep your videos.
Known limitations
- Already heavily compressed videos (for example, downloads from social media) shrink less and can lose visible quality.
- There is no option to change resolution, frame rate, or to trim. Do those in your phone or editor first.
- Maximum Savings is slower than the other levels because of its slow preset.
- HDR footage is converted to standard 8-bit color, so colors can look flatter than the original.
Why we built it this way
We chose a bitrate share instead of a constant quality setting (CRF) because CRF can make an already compressed file bigger, which is the opposite of what people come here for. The trade-offs between the two approaches are explained in CRF vs bitrate. Questions about the pipeline? Write to us.