I’m having a buffering issue as of late and am having trouble determining the cause. When I first set the server up a few years ago I tested a few simultaneous transcoded streams and they played fine. Until recently though I've tended to just direct stream to Rasplex. Because of that I'm not able to say exactly when this started. I’ve carried out quite a few tests using both my main and a test server set up on a laptop in the same LAN so will try to explain the issue clearly (hopefully). It’s a long post but I’ve included some pictures
Main Server Specs
CPU E3-1225 v3 @ 3.20GHz
RAM: 8GB
Ubuntu 16.04 LTS (up to date)
Plex version: 1.1.3.2700
Test (Laptop) Server Specs
CPU i7-4810mq @ 2.8GHz
RAM: 16GB
Windows 10 Pro (up to date)
Plex version: 1.1.3.2700
Clients
Rasplex – wired – latest version
Chromecast
Android Tablet – Nook HD
Dell laptop – wired
HP laptop - wireless
Test Media Specs
Media
Video Resolution 1080p
Duration 2:21:42
Bitrate 7844 kbps
Width 1920
Height 800
Aspect Ratio 2.35
Container MKV
Video Frame Rate 24p
Video Profile high
Part
Duration 2:21:42
File Harry Potter and the Prisoner of Azkaban (2004).mkv
Size 7.76 GB
Container MKV
Video Profile high
Codec H264
Bitrate 6562 kbps
Language English
Bit Depth 8
CABAC true
Chroma Subsampling 4:2:0
Duration 2:21:42
Frame Rate 23.976 fps
Frame Rate Mode cfr
Height 800
Level 4.1
Pixel Format yuv420p
Profile high
Ref Frames 5
Scan Type progressive
Width 1920
Codec AC3
Channels 5.1
Bitrate 640 kbps
Language English
Audio Channel Layout 5.1(side)
Bit Depth 16
Bitrate Mode CBR
Dialog Norm -27 dB
Duration 2:21:42
Sampling Rate 48000 Hz
Main Server Issue
On my main server I am seeing lots of buffering and looking at the ‘speed =>’ output in the ‘Plex Media Server.log’ this seems to point to an inability to transcode at a fast enough speed some of the time. The speed value is very erratic.
The below two screenshots show 2 streams with only 1 transcoding. The transcode is going to the Dell laptop – wired client.
At 19:40 buffering occurs, no real CPU usage can be seen and the speed value is at 0 (it’s not throttled at this point):
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A few minutes later buffering stops, again the CPU is not taxed but the speed values have shot right up:
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Without posting endless examples I am in short seeing regular buffering (even on only 1 stream when transcoding) and very erratic ‘speed =>’ values.
The above example is an extreme one, however I am regularly seeing ‘speed =>’ values of 0.2, 0.3 etc (during which I get buffering) then a while later seeing much higher ‘speed =>’ values.
Most of the time the CPU is doing very little and the fact the CPU can produce higher ‘speed =>’ values suggests it is up to the job.
What could be causing this, it feels like transcoding should be taking place but for some reason it’s just not happening.
Direct Stream is working fine.
Test (Laptop) Server Performance
I’m seeing no issues using a server installed on a laptop in the same LAN, using the same test media. In fact, it can cope easily with 5 streams with pretty steady ‘speed =>’ values in the server log. Below is a screenshot:
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Conclusions
I’m no expert but I am drawing the following conclusions so far:
• As the laptop server can cope with 5 streams with no buffering at the client end I do not have a network issue.
• I know this is simplistic but a comparison between the 2 server’s CPUs is:
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So the laptop server’s CPU is better but based on the above figures I would expect the Main server’s CPU to be able to cope with a few simultaneous transcodes.
What next?
I’m not sure of where to look next so any help/pointers would be appreciated. I’m about at the limit of my knowledge. Ask away if any additional info would be useful.