I am attempting to stream 4K HDR video to a Roku Ultra box. The MKV video file contains 4K HDR video. The video file plays perfectly with VLC Media Player, and is created via MakeMKV with the following attributes:

Length: 02:10:24
Frame width: 3840
Frame height: 2160
Total bitrate: 51884kbps
Frame rate: 23.98 frames/second
Video tracks: HEVC (H265 Main 10@L5.1)
Contains chapters: Yes
Tool name: MakeMKV v1.14.7 win(x64-release)

Audio tracks DTS-HD S24 7.1[Eng], DTS 5.2 [Eng]...
Channels: 8
Audio sample rate 48.000 kHz

Size: 47.2 GB

Item type: Matroska Video File

The Roku device is connected via a wired 1Gb network. The device performance options are set to 4K.
Transcoding is turned off for all devices.

When I attempt to stream the file, the load takes place very quickly, however, only the audio is played. No video is displayed. When I FF the video, the images display in the thumbnails, but after hitting play, the display returns to black with the audio playing.

If I attempt to pre-transcode the file to either MKV or MP4 HEVC, the video displays, however, the color is washed out and faded. Obviously not displaying in HDR. With the MP4 HEVC stream, the video plays for about 5 secs and then displays loading... for about 10 seconds, plays about 5 seconds of video and displays loading... etc. The pre-coded MKV stream, the video plays for about 3 seconds and displays Loading... and freezes. It never comes back. The Mezzmo server shows no activity during this freeze period.

A couple of questions:

1) Why does the pre-transcoded files pause, Loading...? What is Mezzmo doing?

2) Is there no H265 codec transcoding option with the Roku devices?

3) Is the HDR video being sent to the Roku box and Roku is not able to display it or is the video not being sent?

4) Will the transcoding formats MKV and MP4 H264 codecs also pass along the HDR encoding?

I appreciate your help.