Fixing Video Device Switching in Unreal Engine

Issue Description:

Users encounter an issue when attempting to switch the video input device in a game created with the Unreal Engine using the default sample project. The problem occurs after initially releasing the device collection, which prevents further switching as it consistently returns a -1 error.

Platform/SDK:

Unreal Engine with the Agora Video SDK.

Error Message:

Switching the video device returns -1 after calling the release function.

Step by Step Solution:

1. Enumerate the Devices:

Enumerate available video devices using the enumerateVideoDevices() method.

2. Select Desired Device:

Choose the preferred video device and retrieve its deviceId.

3. Switch Device:

Call setDevice() with the chosen deviceId before releasing the device collection.

4. Release After Switch:

Only call the release() method of the IVideoDeviceCollection object after successfully switching the device.

5. Re-enumerate If Needed:

If a device switch is required later, re-enumerate the video devices to obtain an updated list and then repeat steps 2-4.

cpp
// Get device list
auto* devices = videoDeviceManager->enumerateVideoDevices();
char deviceName[512];
char deviceId[512];
// Example: get the first device
devices->getDevice(0, deviceName, deviceId);
// Switch device BEFORE release
int ret = videoDeviceManager->setDevice(deviceId);
if (ret == 0) { // success
   devices->release();
}

Root Cause:

The issue arises because the release() method is called prematurely, which destroys the internal list of devices. As a result, subsequent calls to setDevice() fail and return a -1 error code since there is no list to refer to.

Prevention/Best Practice:

• Treat the IVideoDeviceCollection object as temporary and use it only for short-term tasks.
• Always execute setDevice() before invoking the release() method to ensure the device is correctly set.
• Plan for future device switches by re-enumerating devices whenever additional changes are needed.