Transcoding when you have a rubbish CPU for the task

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Transcoding when you have a rubbish CPU for the task

RS1221+, RS819, RS217
Operating system
  1. macOS
Mobile operating system
  1. iOS
Last edited:
There is a recent NAS Compares video about using something ahead of a Syno NAS to take the burden off the rather poor CPUs when transcoding. Many Syno NASes in recent times have shipped with an AMD CPU with no hardware transcoding, so using a different device for transcoding can make sense. Indeed, it is my preferred method with a Mac mini doing those duties for me.

So what happens if you do need to use an AMD CPU to transcode for Plex - do hang-ups, stalls, buffering and lack of response always await? There is another option that can make the almost impossible, possible - if you have the RAM for it. Thankfully Plex is happy to run a transcode session on a RAM disk and whilst there is no set number of GB you need, it is usually way lower than you would think. More importantly it eases the load on the CPU and makes a typical transcode from 4k down to mobile device-friendly resolutions eminently possible.

So what can you expect? Well this is my AMD-equipped 21+ taking in the high bitrate 4K spectacle of Interstellar (2014) and pushing it out at 720p - something that my 21+ would normally choke on, even with its fast all-SSD array:

20230921-Syno-RS1221-Changing Plex To Use RAM For Transcoding-1.png

Smooth, responsive and with a good buffer margin. The CPU is still working hard but rather than bouncing from 100% load to stalled, it sits around the 80% mark. The main volume is finding life very easy as is the network interface, once the buffers are primed:

20230921-Syno-RS1221-Changing Plex To Use RAM For Transcoding-3.png

Once settled into the movie the transcode load on the system is well within its capability:

20230921-Syno-RS1221-Changing Plex To Use RAM For Transcoding-5.png

The 32GB of RAM in my system is more than most but if you look at the utilisation rate you can see that the actual amount used during transcoding is pretty small, especially as this movie has an unusually high bitrate:

20230921-Syno-RS1221-Changing Plex To Use RAM For Transcoding-8.png

What's the catch Rob, I hear nobody cry. Well, like all RAM disks it is volatile, so if your system dumps then your viewing pleasure or transcode session is over... much the same as without a RAM cache. If you use Plex to record stuff (as I do) then any recording in progress will be completely lost if the system loses power.

Anyway, its easy to try - just add /dev/shm/ as the new transcoder temporary directory:

 2023-11-09 at 16.15.26.png

It does not give the AMD CPU super-powers or even stop those equipped with an older Syno unit with Intel Quick Sync from giggling at you; but at least you have something that can work. For those that use SSDs in their NASes the use of a RAM disk can probably save you many wasted writes during transcoding, so there may be something to this for those users too, with or without Quick Sync.

Just a thought for those with CPUs that are usually left in the dust.


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