3.3.3 Setup 2 - Synology DSM Plex Transcoding

Posted by JTSF at Saturday, July 13, 2013 Read our previous post

Setup 2 - Synology DSM Test Results

Extra Test - Synology DSM Plex Transcoding

This additional test case is to evaluate the performance of my customized NAS when serving as a Plex Media Server and doing video transcoding. Plex transcoding is a highly intensive CPU process. According to Plex FAQ:

How can I tell what speed CPU the NAS needs to have in order to transcode the type of media that I want to watch?

The higher the resolution and the higher the media bitrate the faster the CPU will need to be. As a very general minimum, Plex recommends the following:

•     At a minimum, a Core 2 Duo 1.6ghz CPU
•     For 720p transcoding, a Core 2 Duo 2.0ghz CPU
•     For 1080p transcoding, a Core 2 Duo 2.4ghz CPU

Note, that those specs imply both a specific CPU type (i.e., Core 2 Duo) and a clock speed (i.e. 1.6ghz). Some NAS units use Intel ATOM CPUs. ATOM CPUs are slower than Core 2 duo CPUs when running at the same clock speed. Check online benchmarks that compare the CPU in the NAS to the minimums listed above.....

The FAQ quoted that minimally, the CPU  needs to be a Core 2 Duo 2.0ghz to transcode 720p. We will assess how well the tiny Celeron 847 fares in below tests.


Part I: Plex Transcoding on Customized NAS (Synology DSM)
Video Details

Frame width x height:	1280 x 960
Data rate:	4569kbps
Length:	8mins18secs
1st video:	480p
2nd video:	576p
3rd - 4th video:	720p
5th Video:	1080p

What to do?  1. Please turn on caption, change color of font if necessary.
What to do?  2. Enlarge the YouTube window and select HD 720p quality.
What to see? 3. Observe the CPU utilization while the video plays.

You can also launch the above video in another tab with this link



Part II: Plex Transcoding on Customized NAS (Synology DSM)
Video Details

Frame width x height:	1280 x 960
Data rate:	6000kbps
Length:	9mins50secs
6th - 8th video:	1080p

What to do?  1. Please turn on caption, change color of font if necessary.
What to do?  2. Enlarge the YouTube window and select HD 720p quality.
What to see? 3. Observe the CPU utilization while the video plays.

You can also launch the above video in another tab with this link


 
Test Summary

Base on observations, what have we derived from above tests?

• Videos of the same resolution, have different bitrates. 
• The higher the bitrate, it gets more intensive and challenging for the CPU.
• If the CPU utilization is below 90%, Plex transcoding will be fine.
• If the CPU utilization is near full 100%, the client will have lagging unpleasant viewing experience.

In my build, the NAS has proven to have enough juice to transcode 720p videos and lower bitrate 1080p videos. However, it struggled to handle high bitrate 1080p videos. We also need to remind ourselves that in this test, the NAS is only serving and transcoding to a single client. It would have fail if two or more clients requested different HD feed concurrently. Still, I couldn't have asked for more from a budget Celeron 847 that has a clock speed of 1.1Ghz. Here, I proved that clock speed doesn't represent everything. A lower clock speed processor has delivered a satisfactory job today instead of the recommended Core 2 Duo 2.0ghz.

If you are building your own NAS (BYON) and wants to run Plex Media Server on it with intend to transcode 1080p videos, do consider getting a high end CPU. Having said that, picking a powerful CPU in your NAS build will increase your power consumption. You will need to strike a balance between processing power and power efficiency.