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+--- Thread: SOLVED: Synology NAS high CPU (/t-solved-synology-nas-high-cpu)
Synology NAS high CPU - mbaker - 2025-07-12
I'm a retired IT guy, but completely new to media servers. Hoping someone can help me understand what I'm seeing.
Jellyfin for Docker 10.10.7
Synology DS1522+, DSM 7.2.2-72806 Update 3
CPU usage runs extremely high (80-90%) on certain titles. My libraries include around 70 movies - most Blu-Ray, some DVD - and a handful of TV shows. Of the TV shows two are Blu-Ray, the others from DVD. About a dozen of the movies and one of the TV shows run high CPU, the rest use negligible CPU (1-2%j). All were ripped from disc to MKV. I haven't found much common among those that exhibit the problem, other than they're all Blu-Ray and I don't seem to observe the problem with those ripped from newly-purchased discs. The only other thing that comes to mind is possibly release date; for example, I see the issue with Band of Brothers (2001) but do not with The Pacific (2010). I would have to analyze a bit more to determine if there is any real correlation there.
The difference is stark between titles with the issue and those without; I would post screenshots of resource monitor from DSM but I can't seem to upload anything here, having tried to upload a log already (I'll try another browser later). One will show CPU over 90% and RAM usage 15-20%, the next will show CPU near 0 and RAM 4-5%.
Any information / suggestions will be most welcome.
Thanks,
Mark
RE: Synology NAS high CPU - Efficient_Good_5784 - 2025-07-12
This sounds to me like Jellyfin is just transcoding your videos for your client(s) that don't support the files.
Transcoding is resource intensive. It will use up a lot of resources for a while.
If you click on the playback info in the video player while playing something, it will tell you what's happening.
On top, it will say the following:
Direct Playing == No transcoding
Direct Streaming == Either audio is being transcoded and/or a remux is happening
Transcoding == The video is being transcoded
This is normal. If you want to avoid transcoding:
1. Convert all your media to codecs that are supported on most clients
2. Use a player that can direct play more codecs
If you want to convert your media to another format that can direct play on most things, follow this:
Video: H264 8bit
Audio: 2.0 AAC
Subtitles: SRT
We normally say to set up a GPU for HWA. GPUs can transcode way faster than CPUs in most to all cases.
However, your DS1522+ does not have a CPU with an iGPU. All of Synology's current models that come with an AMD CPU lack any type of GPU, so you're forced to transcode on the CPU cores.
If you want to use a GPU, you're going to need to migrate away from your Synology and onto another system.
RE: Synology NAS high CPU - mbaker - 2025-07-12
Thank you! It all makes sense now.
I had not been able to find a way to view playback info on the Jellyfin players on my TVs, but finally found it in the HTML player. Now I can see that all the titles that do NOT show the issue are encoded H264, and those that do are mostly encoded VC1 or MPEG2VIDEO. That may also partially explain why I have this problem mostly with files ripped from older discs that I've had in my collection for many years; all the new ones I've bought recently are encoded H264.
Do you have a recommendation for a video converter?
RE: Synology NAS high CPU - Efficient_Good_5784 - 2025-07-13
I would check out Handbrake if you want something with a GUI.
Or if you're fine with CLI, ffmpeg would work just fine as long as you know how to use it.