She has a Samsung Galaxy Note 8, while I have a Google Pixel 3. I can cast if the app in question (e.g. YouTube or Hulu) supports casting with a built-in cast button, but if I used the system screen mirroring cast feature from the pull-down menu (say, for an app that doesn't support casting internally, such as Spectrum), I can't cast videos - the part of the screen where the video is appears black on the TV. This sounds like some sort of DRM issue, but why would it only affect my phone and not hers? Is there any way to cast videos from my phone?