Playback

Playback opens a recorded MCAP file and replays it through the same panels you use live. It is an exclusive mode: live ingest pauses while you scrub a recording.

Opening a recording

Open a recording_*.mcap file from the toolbar / file dialog. To open a split session, select all of its parts together — the loader stitches them onto one timeline, order-independently.

Because recordings are self-describing, datavis reads the Protobuf schemas from the file itself. You do not need the original .proto, the --schema flag, or a live source to replay. Channels reconstructed from the file become droppable in the sidebar; leaving replay restores your live channel tree.

Controls

Replay exposes a playback clock over the recording's duration:

  • Play / pause.
  • Scrub anywhere on the timeline.
  • Variable speed from 0.1× to 10×. The clock advances position at speed × wall-time and drives which part of the file is decoded.

Panels update from the store as the position moves, exactly as they do live.

Reading model

As the position moves, panels ask the playback store for a window of samples (snapshot(channel, window)) or the latest sample at or before a time (latest_at). The store answers from whichever chunk(s) cover the requested range. This on-demand decode is what makes very large recordings playable — see Larger-Than-RAM Playback.

Robustness

  • A recording with a gap (from record-queue overflow) loads fine — the store returns whatever subset is present.
  • A decode error inside a chunk is logged and that message skipped; the rest of the chunk still decodes.
  • A topic re-registered with a conflicting type across parts is skipped rather than corrupting the timeline.

Leaving replay

Close replay to return to live mode. Your pre-replay channel tree and layout are restored.