Roku's are not the best streaming media clients due to a limited set of codecs they support. With their version 9.0 code they did add in MPEG2 finally which will help. You might look at what version of Roku code you are running. I also, as a practice, rip my DVDs to a common format. I use M2TS, which is the native Blu-Ray container. MP4 and MKV are equally good. Using a common format will make the streaming client decision much easier going forward. It has worked for me.