black screen playback with audio

[TheDreadPirate]

So the problem is that the image you are using may not include all the OpenCL packages needed for tone mapping 4K content. And I don't have any documentation for adding OpenCL do that package.

The latest (10.8.13) official docker image is broken for Synology NASes due to the newer Intel OpenCL package we use deprecating support for the old Linux kernel Synology uses in DSM (kernel 4.4). The Linuxserver.io image, with their OpenCL mod, should work with your NAS.