Shield Pro Server, HEVC 4K, Fire TV Stick, "an error occurred while attempting to play this video"

Thanks @FordGuy61, that was a very useful reply!

That’s a fair point, I hadn’t fully checked if the Shield Pro 2019 could transcode 4k files, and useful to know about HDR to SDR software decoding! I’ll do some test transcoding to my other non-fire tv devices to see if that’s the issue.

Yep, I was expecting this to transcode, so it may be due to the realtime 4k transcoding you mention. Looking at the logs though it seems to give a decoder error on the client side?

03-31 11:25:30.753  e: [ExoPlayer][EventLogger] playerFailed [eventTime=89.57, mediaPos=0.00, window=0, period=0
  com.google.android.exoplayer2.ExoPlaybackException: MediaCodecVideoRenderer error, index=1, format=Format(0, null, null, video/avc, h264, 18791000, null, [3840, 2160, 0.0], [-1, -1]), format_supported=NO_EXCEEDS_CAPABILITIES
Caused by: com.google.android.exoplayer2.mediacodec.MediaCodecRenderer$DecoderInitializationException: Decoder init failed: OMX.MTK.VIDEO.DECODER.AVC, Format(0, null, null, video/avc, h264, 18791000, null, [3840, 2160, 0.0], [-1, -1])

Useful link, thanks! Interestingly though, the first paragraph says the following, so fingers crossed my transcode test to other devices works ok.