HW Acceleration not being used?

Hi.

I’ve enabled HW Acceleration on my Plex Server (QNAP NAS), and I noticed an immediate reduction in the CPU utilisation.

However, I’m watching a film now which is being transcoded, and the CPU utilisation is up at 90%. I’ve checked the Now Playing section of my Server and it isn’t using HW Acceleration (hw) isn’t in brackets.

Is there a reason why it’s not being utilised? Seems rather annoying seeing as I’m paying Plex for the feature!

The movie is currently playing on an Amazon Firestick 2nd Gen:

Video: HEVC to H264
Audio: AC3 to AAC

Any ideas?

Thanks

Very likely your cpu (gpu) doesn’t have a hardware decoder for hevc