Discovering Devices

Discovering Media Devices

The very first step in using media devices is to discover available devices. To do so, you will use the MediaDeviceQuery.

Querying for Devices

The MediaDeviceQuery class is responsible for finding and reporting available media devices. To begin, simply create one:

// Create a device query
var query = new MediaDeviceQuery();

Behind the scenes, the device query will inspect the system you are running on and find all available media devices. It will then provide all these devices as implementations of the IMediaDevice interface.

// We can now look through devices
foreach (IMediaDevice device in query)

All media devices implement the IMediaDevice interface. To use more specific functionality, perform a type cast to the media device type you need.

Filtering for Specific Devices

The device query allows for only finding devices that meet certain conditions. This is useful for filtering for specific types of devices (like camera vs. microphone) or finding devices that support certain features (like echo-cancelling microphones). To filter devices, simply pass a predicate to the MediaDeviceQuery constructor:

// Find only cameras
var query = new MediaDeviceQuery(
    device => device is CameraDevice

The filter is always of type Predicate<IMediaDevice>.

See the Creating a Query section of the MediaDeviceQuery class for more information.

Using Media Device Criteria

NatDevice includes some commonly-used filters. These can be found in the MediaDeviceCriteria class:

// Find only cameras
var filter = MediaDeviceCriteria.CameraDevice;
var query = new MediaDeviceQuery(filter);

Switching Devices

There are cases where you need to loop through available devices over a long period of time. A good example of this is in camera apps that allow the user to switch cameras. In such cases, the MediaDeviceQuery can be used as a cursor for enumerating through the devices it has discovered. The query provides the current property which returns the device at the current cursor position:

// Create a device query
var query = new MediaDeviceQuery();
// Then get the device at the current cursor position
var device = query.current;

The cursor can be advanced when necessary:

// Advance the cursor
// And now we can use the next device
var device = query.current;

See the Working with Devices section of the MediaDeviceQuery class for more information.

The query will loop back to the first device when it has been advanced to its last device.

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