Braid and Strand Camera
This is the User's Guide for Braid and Strand Camera.
What is Strand Camera?
Strand Camera is a single-camera application for live video acquisition, real-time 2D object tracking, and recording. It runs as a local web server and is controlled through a browser-based interface. You can also control it programmatically via Python scripts. Use Strand Camera when you have one camera and need 2D tracking or video recording, or when setting up and calibrating cameras that will later be used with Braid.
What is Braid?
Braid is a multi-camera system for real-time 3D tracking. It coordinates multiple Strand Camera instances — each running on the same machine or on remote machines — synchronizes their cameras using a hardware trigger, and fuses the per-camera 2D detections into 3D trajectories. Use Braid when you need 3D position estimates of one or more moving objects.
Which should I use?
| Goal | Software |
|---|---|
| Record video from a single camera | Strand Camera |
| 2D tracking from a single camera | Strand Camera |
| 3D tracking with two or more cameras | Braid |
| Calibrating cameras for use with Braid | Strand Camera (one camera at a time) |
Both Braid and Strand Camera are free and open source. You can find the source code on GitHub. Issues and feature requests can be posted on the GitHub issue tracker.
Recording video in Strand Camera
Strand Camera can record compressed H.264 video to MP4 files. Recording is started and stopped from the browser UI or via the Python scripting interface.
Post-trigger recording
The Post Triggering section in the Strand Camera UI allows you to record video that includes footage from before the recording command was given — a "time travel" or pre-roll buffer.
To use it:
- In the Post Triggering section, enter a buffer size (number of frames). Strand Camera will continuously keep this many recent frames in memory. A larger buffer means you can go further back in time, but uses more RAM.
- When an event of interest occurs (or has just occurred), click Post Trigger MP4 Recording. Strand Camera starts an MP4 file that begins with the buffered frames, so the recording includes footage from before the trigger.
- Click the stop recording button to end the recording when done.
The buffer size defaults to 0 (disabled). Set it to a non-zero value before the experiment begins.
Getting started
New users should begin with Hardware selection and then Installation. To go straight to 3D tracking, proceed to Configuring and Launching Braid after installation.
About this book
The source code for this documentation is at github.com/strawlab/strand-braid/tree/main/docs/user-docs/users-guide. This book is made with mdBook.