4K HDR movie buffering when transcoding on DS918+

Plex Media Server NAS & Devices
1

Server Version#:1.23.2.4625 (plexpass) native package
Player Version#: Sony Bravia Plex app (latest)
DSM 6.2.4-25556
DS918+
54 Mbps upload (speedtested)

I have HW acceleration enabled but when trying to watch a 4K HDR movie (no subtitles) remotely there is continuous buffering.

My transcoder settings are:

quality: automatic
buffer: 60
preset: very fast
hdr tone mapping: enabled
disable video stream transcoding: disabled
hw acceleration: enabled
hw accelerated video encoding: enabled
max simultaneous: 2

I turned on verbose logs as described here https://support.plex.tv/articles/201575036-why-is-my-video-stream-buffering/

Looking into my log files, it appears it’s a transcoding rather than a network issue as the transcoder speed according to the logfile averages only around 0.3.

What’s surprising me is that despite this, the CPU utilization is at “only” 60% as seen here:

image
image676Ă—740 83.6 KB

Is this normal and is the DS918+ simply not powerful enough to transcode a 4K HDR movie, even with HW acceleration enabled?

2

DEBUG log files are needed to see what’s happening.

  1. Verify DEBUG logging enabled, VERBOSE logging disabled.
  2. Start playback
  3. let play 20 seconds
  4. Stop
  5. Wait 20 seconds for logs to quiesce
  6. Download logs ZIP file
  7. Attach for review & diagnosis.
3

quality: automatic
buffer: 60
preset: very fast
hdr tone mapping: enabled
disable video stream transcoding: disabled
hw acceleration: enabled
hw accelerated video encoding: enabled
max simultaneous: 2

That is the reason. Disable “tone mapping” and things will go much smoother on the 918+
This is still an unresolved issues for quite some months now.
Alternative at the moment is run Plex in a container “Docker” on your Synology. Then you can have “hardware-accellerated” tone-mapping too.

1 Like
4

@jvanhambelgium

Disable “tone mapping” and things will go much smoother on the 918+

If we do this, won’t the colours be washed out?

Alternative at the moment is run Plex in a container “Docker” on your Synology. Then you can have “hardware-accellerated” tone-mapping too.

How come Plex in a Docker container is able to use HW for tone mapping, and the native Synology package isn’t? Shouldn’t it be the other way around?

5

Indeed colors are a bit washed out without the proper mapping.

Don’t know exact anymore what causes this, you should scroll through the topic and its mentioned somewhere in there about the action needed to fix it.

But concerning this, it seems to be quite for several months now on this. I guess everyone is working on stabilizing Plex for DSM7.0 or something? Don’t know.

6

Don’t know exact anymore what causes this, you should scroll through the topic and its mentioned somewhere in there about the action needed to fix it.

What topic?

7

I believe he’s referring to this post: HW acceleration not working in docker container on DS918+ - #31 by Alain13

1 Like
8

This one also contains some info on it :

9

Would you like this resolved ?

This isn’t rocket science.

  1. Docker relies on the host providing access to the hardware
  2. Access to the hardware is controlled by udev rules.
  3. The native package writes the rules when it’s installed.
  4. DSM updates reset (erase) the rules the native package wrote.
  5. Reinstalling the native package writes the rules again.
  6. If using Docker, the native package may be uninstalled once the rules are written.
  7. With fresh UDEV hardware access rules written, Docker will also now work.

Why is it this way?

  1. Plex is not “root” on DSM.
  2. Plex runs as non-privileged user plex in group users
  3. Docker containers also run as non-privileged user id.
  4. The UDEV rules create a GROUP rule which allows access to the hardware,
  5. Native package user “plex” is a member of that group.
10

The native package writes the rules when it’s installed.
DSM updates reset (erase) the rules the native package wrote.

Are you saying that upon installing the native package (aka the Synology PMS rather than the Docker PMS), HW accelerated tonemapping is supported until a DSM update is applied? Or, putting it another way, reinstalling PMS after a DSM update ensures that HW accelerated tonemapping will always be available?

11

@ChuckPa I’m confused by your answer…

It looks to me that what you’re saying is that installing the PMS Synology package should give it access to the rules required to properly transcode tone mapped HDR, as long as we don’t install any DSM updates (which override those rules). Correct?

If that’s the case, I don’t understand why it’s not working for me, because I just installed the latest PMS version by downloading the latest Synology package from Plex’s website (which should’ve written the required rules for transcoding tone mapped HDR), and have not installed any DSM updates in the meantime.

As other users, I’d prefer to keep using the native Synology package instead of migrating to Docker, but would like to have HW transcoding working all the time, and so far it’s not working with tone mapped HDR.

1 Like
12

May I see an actual set of log files (DEBUG logging on, VERBOSE logging off) which captures what’s happening?

…as I requested 25 days ago —

  1. Verify DEBUG logging enabled, VERBOSE logging disabled.
  2. Start playback
  3. let play 20 seconds
  4. Stop
  5. Wait 20 seconds for logs to quiesce
  6. Download logs ZIP file
  7. Attach for review & diagnosis.

EDIT

If using docker, please also show me the docker config

13

@ChuckPa

May I see an actual set of log files (DEBUG logging on, VERBOSE logging off) which captures what’s happening?

I’d prefer to not share the logs publicly, is there an e-mail I can send them to?

…as I requested 25 days ago —

I’m sorry, but I’m not the author of this topic, and I wasn’t having this problem 25 days ago.

If using docker, please also show me the docker config

I’m not using Docker, and I’d prefer to not use Docker. If this could be fixed with the native Synology package, I’d prefer to keep using that.

14

I’ve changed my mind, and I’ve decided to migrate my current installation to Docker. Everything seems to be working better, but here’s something I’ve noticed:

  • Convert to 1080p HD (High) 20 Mbps

    • With HDR tone mapping: Buffers every 10 seconds :x:
    • Without HDR tone mapping: Doesn’t buffer :heavy_check_mark:

  • Convert to 1080p HD (Medium) 12 Mbps

    • With HDR tone mapping: Doesn’t buffer :heavy_check_mark:
    • Without HDR tone mapping: Doesn’t buffer :heavy_check_mark:

However, and I’m not sure if this is a bug, but when I select Convert to 1080p HD (High) 20 Mbps, the Dashboard shows me the following:

image

Can you see what’s wrong? It’s transcoding from 4K to 4K, but I’ve picked “1080p (High)”, so why am I getting a 4K output instead of 1080p?

Maybe that’s the reason why it’s buffering in that particular case, or maybe not, because I get a 4K to 4K transcode both with and without HDR tone mapping enabled with the “1080p (High)” option (but only the one with HDR tone mapping buffers every 10 seconds).

Thoughts?

15

Does this apply to DSM 7 as well?

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DSM 7 is an entirely new platform as far as all applications are concerned. Docker is no exception.

In the native DSM 7 package, I request DSM grant access to the hardware.
In the native DSM 6 package, I configured access myself.

Synology has dropped Docker from several NAS models; my development system included.

The most I can suggest –

  1. Review your hardware device specification.

  2. Expect to change (adjust) it for DSM 7.

Check with docker forums or syno forums where someone might have already figured out the new dance.

17

Hi,
I have the same problem with my Sonology DS918+ (DSM 7) with Plex (1.24.2.4973, native instalallation with the official package) ?
What’s the recommended way to take advantage of hardware acceleration?

19

Isn’t this akin to saying don’t transcode 4K HDR altogether? I don’t really see any point in doing it without tonemapping as the resulting stream is not really watchable.

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@TrntRzr1911

Bingo.

Now you get into the whole argument about “Why have 4K HEVC HDR content if you have to transcode and tonemap it ?”

Silly, isn’t it?

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