How to choose input video device for webrtc?

In WebRTC, selecting input video devices involves the following steps:

1. Retrieve Device Information

First, use the navigator.mediaDevices.enumerateDevices() function to obtain information about all available media input and output devices on the system. This function returns a Promise that resolves to an array of MediaDeviceInfo objects. Each MediaDeviceInfo object contains properties such as deviceId, kind, label, and groupId.

javascript
async function getDevices() {
  const devices = await navigator.mediaDevices.enumerateDevices();
  return devices.filter(device => device.kind === 'videoinput');
}

2. Select Video Device

Once the list of video input devices is obtained, users can select a specific video device using the device name or other identifiers. In practice, this is typically implemented using a dropdown menu for user selection.

3. Request Video Stream

After selecting a device, request the video stream using the navigator.mediaDevices.getUserMedia() function by specifying the deviceId to target a specific video input device. The constraints object is used to define media types and the exact device ID.

javascript
async function getStream(deviceId) {
  const constraints = {
    video: {
      deviceId: { exact: deviceId }
    }
  };

  try {
    return await navigator.mediaDevices.getUserMedia(constraints);
  } catch (error) {
    console.error('Error accessing media devices.', error);
  }
}

4. Display Video Stream

Once the MediaStream is obtained, it can be bound to a <video> element to display the video.

javascript
function playVideoFromStream(stream, videoElement) {
  videoElement.srcObject = stream;
  videoElement.play();
}

Practical Application Example

Suppose in a web application, you need to allow users to select a video input device from available options and then display the video stream from that device.

1. List devices - Display a dropdown menu on the page listing all video input devices.
2. User selection - Users select a device from the dropdown menu.
3. Request and display video - Request the video stream based on the user's selection and display it within a <video> element on the page.

This process not only ensures users can freely select input devices but also programmatically guarantees flexibility in device selection and the specific implementation of functionality.