I am not able to get screen mirroring (aka AllShare cast in past) working with my Samsung S3 and Roku HDMI stick attached to my TV.  Everything works fine but I just get a black screen on TV.  I can hear the sounds of taps and it seems the devices are properly connected but it would just refuse to display any picture on TV.

I have got my phone rooted and added wlan.wfd.hdcp=disable in build.prop file.  Earlier I was getting HDCP not supported error but I fixed it by adding this line. 

I cannot make head and tail of this problem and banging my head against wall for two days.  There is no error displayed anywhere which makes it harder to troubleshoot.  I can screen mirror correctly with my Samsung Tablet so there is no problem with Roku at other end.