File formats
CS2 Demo File Formats: .dem, .dem.zst, and .dem.bz2
The demo content can arrive as a raw .dem file or inside a compressed representation. Compression changes transfer size, not the fact that the underlying asset is a game replay rather than video.
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What each extension means
- .dem is the raw replay file consumed by the game or parser.
- .dem.zst is a demo compressed with Zstandard.
- .dem.bz2 is a demo compressed with bzip2.
- .mp4 is an encoded video output and cannot be parsed as a match demo.
Upload behavior
Small raw demos can upload directly. Larger raw demos may be compressed in the browser before multipart upload. Already compressed supported formats can pass through without being recompressed first.
Keep identity and cache safe
- Use file identity plus parser and schema version for local cache reuse.
- Reparse when parser behavior or schema changes.
- Do not treat temporary uploaded demos as permanent public assets.
- Keep completed videos as the durable result.
Frequently asked questions
Should I extract a .dem.bz2 before uploading?
It is not required when the upload flow supports that compressed demo format. Keeping it compressed can save transfer time.
Can I rename a video to .dem?
No. Renaming the extension does not convert encoded video into game replay data.