I recently picked up a DS918+, set up Plex, and began ripping my library of Blu-rays. I am currently ripping the movies with MakeMKV and leaving them untouched. I am attempting to view the movies on the Plex web client and an Apple TV 4K. For both clients I am experiencing consistent stuttering on some titles, and I am unable to figure out what is the cause. I'm currently using PMS 1.12.0.4829, Plex Web 3.37.2, and the latest tvOS (11.2 I believe).
When streaming on the Apple TV, Plex reports the video is a direct stream, and audio is transcoding DCA to AC3. For Plex Web, it's direct stream video and transcoding DCA to AAC for audio. In both cases, the CPU utilization on the NAS is quite low; almost always <5%. This suggests, to me, that the video and audio stutter I'm experiencing are not due to a CPU bottleneck on the server.
Regarding the network, everything is wired together with gigabit cable, with a gigabit router and switch inbetween. I can transfer a 40 GB MKV from the machine running the Plex Web client to the NAS within a few minutes. I cannot easily run a speed test between the Apple TV and the NAS, but I am confident the network is not at fault here.
I downloaded the Plex server logs, but to be honest I'm not really sure what I'm looking for. I read in another thread here that this log line can sometimes be telling if the 'speed=' field is <1, but that's not the case here.
Mar 11, 2018 17:21:42.152 [0xf1511b40] DEBUG - Completed: [127.0.0.1:56510] 206 PUT /video/:/transcode/session/369F5CC2-E3C8-42B2-B553-063A42883DD7/b781d1f2-73b5-4afc-89d2-a5b3e6731393/progress?progress=52.8&size=-22&remaining=100&speed=19.9 (12 live) 1ms 342 bytes
Other than that, all of the information I've found so far by Googling seems to suggest this is an issue with either a lack of CPU power or a network bottleneck, but neither seems to be the case here. I have not yet attempted to re-encode these files; I'd really prefer to avoid it if I can. Not all titles are experiencing this behavior; some movies play just fine under the same conditions (direct stream video, transcode DCA to AC3/AAC audio). The two movies I've been primarily testing with today are both H.264 video and DTS audio. One plays fine and the other does not. Both are untouched rips from MakeMKV.
Any ideas? I'd be happy to provide more logs or any other info if that will help.