I have read that Roky Ultra are not supposed to transcode if:
Native playback of 4K content is supported so long as it meets the following criteria:
Resolution: 3840x2160 or smaller
Video Encoding: H.265 (HEVC; both 8-bit and 10-bit) or VP9
So why it transcode the video and audio, my file seem to respect the requirement...
See the details of my mkv in the attachment.