sync_viewer

A lightweight, web-based debug viewer for the OTIO Sync protocol. It joins a sync session as a passive observer — it receives all state changes but never acts as master or sends events.

Overview

The viewer runs a FastAPI + WebSocket backend (server.py) that connects to RabbitMQ and streams live session state to a browser UI. It is useful for:

• Watching the timeline state as a session progresses
• Verifying playback and display sync between hosts
• Inspecting clip and track metadata in real time

It does not require an RV or xStudio plugin to be installed.

Requirements

pip install -r requirements.txt

Dependencies: fastapi, uvicorn[standard], opentimelineio.

server.py also imports otio_sync_core from the parent python/ directory. When run from the sync_viewer/ directory this is handled automatically via a sys.path insert.

RabbitMQ must be reachable (default: localhost:5672).

Usage

cd sync_viewer
python server.py [options]

Open http://localhost:8765 in a browser.

Options

Flag	Default	Description
--host HOST	localhost	Web server bind address
--port PORT	8765	Web server port
--rmq-host HOST	localhost	RabbitMQ host
--rmq-port PORT	5672	RabbitMQ port
--session SESSION	otio-sync-demo	Session ID to join

UI

The browser UI has three panels and two status bars:

Left sidebar — lists all timelines in the session. Click to switch which timeline is displayed.

Centre — timeline viewer — shows all tracks (Video, Audio, Annotations) as coloured clip blocks. Gaps are rendered in grey and are not selectable. Annotation clips appear as 1-frame-wide amber marks; zoom in to inspect them.

• The red playhead line shows the master’s current playback position.
• The green glow highlights the clip currently under the playhead.
• Follow mode (top-right of zoom bar) auto-scrolls to keep the playhead in view. Click to detach.
• Zoom: + / − buttons, Fit to reset, or Ctrl+scroll with the mouse wheel.

Right — Inspector — click any clip to load its full OTIO JSON with syntax highlighting.

Playback bar (bottom) — shows playing/stopped state, current time, frame, FPS, and loop flag.

Display bar — shows the master’s viewport state: pan, zoom, exposure, and active channel (R/G/B/A/RGBA).

Top bar — shows the session status badge (SYNCED, JOINING, DISCOVERING), the master peer GUID, and this viewer’s own GUID. A ★ master indicator appears if this viewer somehow becomes master (unexpected in normal use).

REST API

The server also exposes a few debug endpoints:

Endpoint	Description
GET /api/state	Full session state snapshot as JSON
GET /api/debug	Raw OTIO timeline structure dump; useful for diagnosing missing clips or bad durations
GET /api/detail/{guid}	Full OTIO JSON for any object by GUID

Notes

• The viewer uses outlier rejection when calculating timeline duration for zoom-to-fit. If a clip has a bogus large duration (e.g. a 10,000-frame fallback), it is dropped from the fit calculation so the view is not dominated by it.
• When a master switches sequences, the viewer automatically follows the new active timeline.
• The viewer re-requests session state if it gets stuck in JOINING for more than 10 seconds.