Download of transcoded video never faster than 4 MBit/s although CPU only at <1% on DS918+ Synology

[Steggl]

Server Version#: 1.32.8.7639
Player Version#: Any Webplayer, any iOS player

Hi community, I hope that you can help me out here. For almost forever (years now!) I have had the issue that the transcode and download functionality on my Synology DS918+ with Intel hw transcoding has never really worked.

If I want to transcode a video (tested today again by my daughter) from e.g. 2160p to 720p I never get download speeds >4 MBit/s (even within the LAN and my internet connection is 20 MBit/s up) while the Plex CPU utilisation is around 1%, the system at around 10%. The Plex server is installed via docker and HW acceleration active via the usual guides, when I am playing in the LAN or remotely I can see the (HW) in the dashboard, so I assume that it is working properly and it works nice converting 4k to 1080p in real time down to 12Mbps as we can see here:

BUT why is the download speed always only 4 MBit/s (swinging between 2-6 MBit/s) even in LAN and never saturating either CPU or the network? For me the download feature is useless at it is, as it always takes forever to do so.

Can you please enlighen me what I might have missed, which logs do you need to help me resolve this $%$*#2 situation?

Thanks community!

[ChuckPa]

What are your Video Quality settings.

I have both set to Maximum

When I download a TV episode (H.264), a 2.5 GB file will download in seconds

When I download a 30 GB UHD, it is transcoded for the iPad and takes about 10 minutes. Transcoding is software (not hardware) so that part will slow it down.

Maybe this is something which the iOS app and PMS can change to Foreground mode rather than Background downloading (which would allow HW to be used).

Your thoughts?

[Steggl]

Hello @ChuckPa, thanks for your feedback.

I have set it video quality setting to max. 12 MBps as my upstream link is only 20 MBit/s. Downloading a file (e.g. a TV show in 1080p) in original quality to my iPad does 200-300 MBit/s in LAN and therefore is not an issue but what we all want is taking our 4k HDR videos on the road transcoded into 1080p.

I have - of course - the app always in the foreground on iOS (14Pro) and iPad OS but I can never get beyond the 4 MBit/s, which should not be a surprise as only 1-2% of the NAS (Synology DS918+, Intel Celeron J3455, Apollolake) CPU is being used. I tried my Samsung S21 5G with the same use cases to find out if it was an iOS issue but it is slow as well, taking about 1h to download a 11GB video file:

From which platform are you downloading, a Windows PC?

So my two questions:
a) If it has to be in SW, why not use as much CPU budget as you can get from the OS?
b) Why not transcode with HW support as with streaming? That does not make any sense.

[ChuckPa]

I am downloading from my Linux host. (it has 1000 passmarks per core)

Here, I am downloading the 3-episode series “1066”.

The CPU load is minimal because it’s converting the MKV → f’MP4 for iOS (2017 iPad Pro)

Here’s a 29GB file which was both transcoded and downloaded in 13 minutes

Looking at the filename you show, my first question is “How many unwanted tracks exist in that file ???”

I also see DoVi Profile 8 which is a Hybrid / artificial DoVi file. The bitrate of the file (low) confirms it’s not a full rip and has been ‘cooked’

I see two issues here.

Let’s set the media itself off to the side for now.

What is the association speed of the iPad ? Does it really perform at speed ?
I have only 1 other app open on the iPad at the time I’m testing this.

Are you getting a software transcode (which is slow on the Syno because of its lower CPU performance) ?