Webcamtexture at 1080p 50fps produces black image

I'm trying to get the 1080p 50fps video from a blackmagic intensity pro 4k as the texture of a plane, but have only managed to do so when I set the camera to 1080i. I'd like to get progressive video, so I've tried setting the requested resolution and fps up in the webcamTexture constructor, but it changes nothing:

 void Start () {
         //webcamTexture = new WebCamTexture(WebCamTexture.devices[1].name, 1920, 1080, 50);
         webcamTexture = new WebCamTexture();
         webcamTexture.deviceName = WebCamTexture.devices[1].name;
         Renderer renderer = GetComponent<Renderer>();
         renderer.material.mainTexture = webcamTexture;
         webcamTexture.Play();
         Debug.Log(webcamTexture.deviceName);
 }