I use DS Video on Apple TV - works perfectly (incl. DTS transcoding). However, I don't transcode UHD, only 264, so I suspect that the reason for the judder is a too weak internet connection.

Again to the actual question: Does 1080p or even 4K transcoding work with Plex? On the 214play, which is exactly what it is made for, transcoding with HW support only works with the DS apps, Plex does not support Evansport HW transcoder, so not even 1080p smoothly. A joke!
And it's also lame in other ways...

I don't see any major differences between the 216play and the 216+ II except for the CPU, encryption module and connections. The play seems like a respected +... 4k transcoding is specified for both. But also with Plex or only DS Video?

According to Synology-HP, both H.264 and H.265 are now supported.

https://www.synology.com/de-de...