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+### The `visca` backend
+
+The `visca` backend provides control of compatible PTZ (Pan, Tilt, Zoom) controllable cameras
+via the network. The VISCA protocol has, with some variations, been implemented by multiple manufacturers
+in their camera equipment. There may be some specific limits on the command set depending on the make
+and model of your equipment.
+
+This backend can connect to both UDP and TCP based camera control interfaces. On Linux, it can also control
+devices attached to a serial/RS485 adapter.
+
+#### Global configuration
+
+The `visca` backend does not take any global configuration.
+
+#### Instance configuration
+
+| Option	| Example value		| Default value 	| Description							|
+|---------------|-----------------------|-----------------------|---------------------------------------------------------------|
+| `id`		| `5`			| `1`			| VISCA Camera address (normally 1 for network communication	|
+| `connect`	| `10.10.10.1 5678`	| none			| Camera network address and port. Default connection is TCP, when optionally suffixed with the `udp` keyword, connection will be UDP |
+| `device`	| `/dev/ttyUSB0 115200`	| none			| (Linux only) Device node for a serial port adapter connecting to the camera, optionally followed by the baudrate |
+| `deadzone`	| `0.1`			| `0.1`			| Amount of event value variation to be ignored for relative movement commands |
+
+#### Channel specification
+
+Each instance exposes the following channels
+
+* `pan`: Pan axis (absolute)
+* `tilt`: Tilt axis (absolute)
+* `panspeed`: Pan speed
+* `tiltspeed`: Tilt speed
+* `zoom`: Zoom position
+* `focus`: Focus position
+* `autofocus`: Switch between autofocus (events > 0.9) and manual focus drive mode
+* `wb.auto`: Switch between automatic white balance mode (events > 0.9) and manual white balance mode
+* `wb.red`, `wb.blue`: Red/Blue channel white balance gain values
+* `home`: Return to home position
+* `memory<n>`: Call memory <n> (if incoming event value is greater than 0.9)
+* `store<n>`: Store current pan/tilt/zoom setup to memory <n> (if incoming event value is greater than 0.9)
+* `move.left`, `move.right`, `move.up`, `move.down`: Move relative to the current position. Set speed is multiplied by the event value.
+* `move.x`, `move.y`: Move relative to the current position along the specified axis. Set speed is multiplied by the event value scaled to the full range (ie. `0.0` to `0.5` moves in one direction, `0.5` to `1.0` in the other).
+
+
+Example mappings:
+
+```
+control.pan > visca.pan
+control.tilt > visca.tilt
+control.btn1 > visca.memory1
+control.stick_x > visca.move.x
+control.stick_y > visca.move.y
+```
+
+#### Compatability list
+
+| Manufacturer	| Exact model(s) tested		| Compatible models				| Result / Notes					|
+|---------------|-------------------------------|-----------------------------------------------|-------------------------------------------------------|
+| ValueHD	| VHD-V61			| Probably all ValueHD Visca-capable devices	| Everything works except for absolute focus control	|
+| PTZOptics	| 				| Probably all of their PTZ cameras		| See ValueHD						|
+
+#### Known bugs / problems
+
+Value readback / Inquiry is not yet implemented. This backend currently only does output.
+
+Some manufacturers use VISCA, but require special framing for command flow control. This may be implemented
+in the future if there is sufficient interest. Some commands may not work with some manufacturer's cameras due to
+different value ranges or command ordering.
+
+Please file a ticket if you can confirm this backend working/nonworking with a new make or model
+of camera so we can add it to the compatibility list!