The beta is certainly pretty and generally working well for me. However, I have run into an issue that affects me and probably others whose servers do not support transcoding very well. The problem has to do with subtitles. I first ran into this on a Japanese-language blu-ray that has also has an English audio track. The English audio track is the default, but I would prefer to hear the original and see the English captions that also come with the disc.
Playback is smooth and continuous if captions are turned off. It starts and stops (with loading screens while stopped) if captions are turned on. Clearly, this is due to transcoding at the server end. I am running Emby server on my Synology 1813+, which has no hardware support for transcoding. FWIW, the video quality setting in the Roku app is set to AUTO.
I have replicated this problem with another 1080p video. Turning on captions also causes the same behavior. I can supply log files if that would help, but from these data points it is pretty clear that the issue is transcoding at the server end.
Is there any workaround for this? My Roku 4 is connected via HDMI to a Marantz av7702mkii receiver, and that sends the video via HDMI to an LG OLED65B6P UHDTV. Both the receiver and the HDTV have their own video decoding capabilities, so even if the Roku 4 may not be able to handle captions (I am not sure), either the receiver or the HDTV may be able to. Perhaps the answer to this is to put an option in the Roku app that tells it to take anything the server has directly (no transcoding at the server end) and then pass along anything that IT cannot transcode to whatever is upstream.