Archive from another server (remotes)¶

Sapsan can seamlessly play an archive that is recorded (or used to be recorded) on another server. A stream lists remote servers — and their archives become an extension of the local one: the viewer sees one continuous archive and never knows where the data physically comes from.

Typical tasks this solves:

• migrating to a new server without losing history — the new one records fresh archive, the old one keeps the past;
• reading the archive from replica servers;
• recovering after a disk replacement.

Configuration¶

streams:
  cam1:
    inputs:
    - rtsp:
        url: rtsp://10.0.0.5/stream0
    dvr: {}
    remotes:
    - url: http://old-server:5080
      timeout_ms: 5000

There can be several remote servers — Sapsan queries them all.

How seamlessness works¶

On every archive access Sapsan merges local and remote data:

• Archive bounds — the union of all servers' ranges: the earliest start and the latest end. In UIs and the API the stream looks like one continuous archive.
• Playlists — fragment lists from the local DVR and all remote servers are merged, sorted, and deduplicated. There is no seam, gap, or duplicate at the junction of two archives.
• Fragments — read in a cascade: live buffer → local DVR → remote server. The fragment URL is the same for the player regardless of where the data lives.

This is possible thanks to Sapsan's absolute fragment addressing: a fragment's name is its UTC time, so the same fragment has the same name on every server, and merging archives requires no timeline remapping.

Lazy replication¶

A fragment read from a remote server is automatically written into the local archive. The local DVR gradually "pulls in" the parts of foreign history that viewers actually watch — and over time stops fetching them over the network. A failure of such a write never interferes with serving the viewer.

Failure behavior¶

• If a remote server is unreachable but the data exists locally, playback continues; the problem is only logged.
• Sapsan remembers which ranges are absent on a remote (negative cache) and does not re-query it for missing data.
• Init fragments of remote streams are cached.

Next steps¶

• Configure DVR recording
• Play the archive