Hardware transcoding does not work anymore

Plex Media Server NAS & Devices
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Server Version#: 1.15.6.1079-78232c603 (Synology NAS DS218+ with DSM 6.2.2-24922)
Player Version#: 3.100.1 (PC with Windows 10 Pro x64)
Player Version#: 7.16.1.10610 (smartphone with Android 8.0.0)

Hello Plex community!

I am a new Plex Pass member.

My NAS is compatible with hardware transcoding.

15 days ago I subscribed to the Plex Pass in order to enjoy hardware transcoding.

I restarted the PMS and actually enjoyed hardware transcoding (witness the “(hw)” indicator besides the “Transcode” format of the played videos). It was great! (NAS CPU load below 30 % in the dashboard)

Today, after experiencing an annoying and unexpected stuttering while watching a video, I had a look at the NAS CPU load in the dashboard: 100 %! (and no more “(hw)” indicator besides the “Transcode” format of the played video)

Why does the PMS not do hardware transcoding anymore?

This issue is not dependent on the client (it happens with all my clients - Android, Windows) and it is not dependent on subtitles (it happens with or without them - I have read the “READ ME FIRST: About Synology” and the “Synology FAQ’s … Read This First!” with its Q21 which says that “transcoding of subtitles cannot be performed in hardware”).

Obviously the box “Use hardware acceleration when available” (in the PMS transcode settings) is checked since my subscription to the Plex Pass.

I have tried to restart the PMS but the issue is still there.

Software transcoding is not an option for me (my NAS is not enough powerfull for that - unless sacrificing the resolution down to 720p or worse, 480p) and hardware transcoding is the only reason I came to Plex Pass…

I am confused. Any help/lead will be greatly appreciated. I am pretty sure I had not changed a thing which could be involved into generating this issue (neither in the PMS settings nor in the PMP ones)… but I might be wrong. I must have changed something, at least I hope.

I have pretty big video and music libraries. So uninstalling and reinstalling the PMS and all the clients would be the last move for me (it took days to retrieve all the meta-data).

Regards,
JerHome.

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I would suggest you try to play a video while monitoring the server log console and watching for entries with MDE:

these should give you an idea why is plex is deciding to transcode.

then you can look in the same area of logs for info on why it is not hardware transcoding

like perhaps ffmpeg, or codecs errors

Plex > settings > console > filter

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Hello TeknoJunky,

First of all, thank you very much for your answer.

I have followed your advice and had a look into the PMS log.

I saw a lot of errors (and some about missing libraries…)

A pretty big mess in there. So I resigned myself to reinstalling completely the PMS (and to deleting the Plex directory and the plex user).

After this reinstall I had a look at the Synology Disk Station Manager settings and… I found out what had happened in the first place.

The answer is in this community announcement by ChuckPA

Shame on me… Moved by a cleaning compulsion (not an OCD symptom but close) I had this wonderful idea of deleting the Synology user group called “video” (this group is created during the PMS install). As ChuckPA says in his community announcement, this user group is mandatory (now I know) for providing to the plex user the access (special privileges) to the hardware acceleration ressource of the NAS.

I am a bit sad that now I have to rebuild all my libraries, but I am glad the hardware transcoding is working again. Moreover I am not sure it would have been possible to (re)create this special “video” user group manually…

Regards,
JerHome.

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To add to Trumpy’s post,

Video group is pre-installed by Synology. If you delete the group, you only need to go to Control Panel - Groups:

  1. Create the group
  2. Uninstall the Plex package . Do not delete anything else
  3. Reboot the Synology
  4. Install Plex
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Hello Trumpy and Chuck!

That’s valuable info you gave me there… Unfortunately I had already deleted the Plex folder and the plex user to get a clean install when I received your messages.

Everything is working now and I am relieved (and my libraries have been rebuilt since yesterday).

Thank you! May this post and you answers help future Synology Plex-Pass members in trouble.

Regards,
JerHome.

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