navigator.mediaDevices deviceId not working on Flutter

I am making an app with video calls using flutter, I am currently getting the video stream using the following code:

 Future<MediaStream> _getLocalVideoStream(dynamic navigator) async {
    _loadCamerasInfo();
    return navigator.mediaDevices.getUserMedia({
      "video": {"deviceId":"0"},
      "audio": false
    });
  }

This should open the back facing camera but the front facing camera is opened instead, I have also checked all of the media devices like so:

List<MediaDeviceInfo> deviceInfo =
        await navigator.mediaDevices.enumerateDevices();

Iterating over the deviceId attribute of each item in deviceInfo results in the following values: 0,1,2,3 which means that 0 should correspond to one of the cameras however no matter which id I use from this list in the _getLocalVideoStream function the same default front facing camera is used instead.

How can I correct this so I can cycle through the different cameras of the device? (I am testing this on a real Android device)

First off, when you use navigator.mediaDevices.enumerateDevices(); it will return all mediaDevices. This includes microphones, headsets and cameras. So it is possible that deviceId 0 is not a camera and could be a microphone.

Secondly when you list your constraints:

{
  "video": {"deviceId":"0"},
  "audio": false
}

This is not a respected constraint for the device Id, meaning that it could possibly ignore your request for the device Id and just pick the first video device it finds. You can modify the constraints to look like below:

{
    "video": {
               "deviceId": {
                  "exact": someId
               }
             }
}

Using the exact keyword will force it to use that Id. There is a helpful page that goes over all of this here

Further more, if you don't want to search for a specific deviceId and use that. There is a helpful keyword you can use called 'facingMode', this is primarily for mobile devices. It can be used to set a preference for what type of camera you would like. For example facing the user, or facing the environment. Please take a look at the example below:

"video": {
           "facingMode": "user" //prefers front camera if available
//      or "facingMode": "environment"  --> perfers rear camera if available
         }