Server Version#: 4.48.1
Player Version#: Web (Chrome)
Having some serious issues with transcoding on a few files, anytime this problem presents it involves a .mkv file, although not all .mkv files cause problems, currently my problem is with a 4K x265 .mkv 5.2GB file (all of the current top peer episodes of The Mandalorian).
The problem is that the stream keeps buffering every 10-15seconds, when it plays every second or so a few frames is all blocky and messed up, my CPU stays around 60-70%, GPU around 20-30% and disk/network negligible, I cannot choose “original quality”, the top choice is 4K 37.5Mbit which when i select it goes to “convert automatically” (which sucks by the way, sever should not overrule a manually set quality).
I have hardware acceleration turned on, most files use far more than 20-30%, not sure why it seemingly only uses CPU to transcode this file, I have also run many similar files, including files from the same series about same size with no issues at all before, to be clear, I have tried several different files of this episode, all 4.9-5.2gb size, they all have problems.
My server:
CPU: R7 1700
RAM: cheap 32gb 3200MHz ram, 16gb used for RAM disk
HDD: 2x8TB HDD 1x 4TB HDD
GPU: Radeon 7990
Network: 1Gbit
OS: Win 10 Pro
Thank you for the information, but should it really be that hard to transcode? I thought transcoding was fairly easy when it was from and to the same resolution.
Edit: Oh, and is the graphics card too old for that codec? I figure maybe thats why it didnt do much when this file was transcoding.
Video transcoding is compute intensive, especially for 4K video. The more pixels to process the more compute resources are required. It does not matter if the in/out resolution is the same. For 4K your server still has to transcode 8.3 million pixels roughly 24 to 30 times a second (3840x2160 & video frame rate).
If your GPU does not support HEVC video, your system will struggle to transcode 4K media, especially 4K HDR. Plex guidelines recommend a CPU with roughly a 17K Passmark is to transcode 4K HDR using the CPU. Your CPU has a Passmark of 14K.
Plex Dashboard -> Now Playing will show if your system is is transcoding and if it is using hardware acceleration. See the screenshot below. The (hw) shows that hardware acceleration is used for the transcode.
There are two parts to a transcode: Decoding from the current format and encoding to the desired format.
Depending on the capabilities of your graphics card, your system may use hardware acceleration for only a portion of the transcode.
For example, if your graphics card does not support HEVC decoding, the server will use the CPU to decode the video, and you will not see a (hw) in the Plex Dashboard for the decode portion of the transcode. If your graphics card supports encoding to H.264, you would still see the (hw) for the encode portion of the transcode.
Only question I have left now is how come it’s always a .mkv container I have these issues with, is it just coincidence or is there something about .mp4 that makes it easier to transcode?
The container does not matter for transcoding. Only whether the client supports the selected media types.
Not all clients support both MP4 and MKV containers. If the Plex client supports the media types but does not support the container, then Plex will Direct Stream the media (and Plex Dashboard will show Direct Stream instead of Direct Play).
Direct Streaming is just Plex remuxing the media to a supported container. It requires very little CPU and should not be a concern with your system.
I’ve never seen a list of which clients support which containers. My Android mobile & Android TV clients support both. Not sure about other clients.
