Transcoding speed <1.0 with HW @ Tone Mapping

Plex Media Server
,
1

Server Version#: 1.25.2.5319 (Ubuntu x64)
Player Version#: 3.9.0 / 5.29.1 (WebOS)

Hey guys, I’m really at a loss. Without subtitles everything runs optimally, encoding speed at 3.6 to 4.8. As soon as subtitles are activated (also SRT) they are burnt in. This seems to be a limitation of WebOS. The result is encoding speed from hell.

Is it normal that the iGPU 630 can’t even manage a single 2160p HDR to 1080p SDR with SRT-Burn-in? The CPU/GPU load is always under 30%.

All other clients run smootlhy with SRT-Direct Play, unfortunately most of the family clients have WebOS.

2

Burning in of subtitles can only be handled by the CPU – this cannot be done using hw-transcoding.

3

Ok, but the CPU is only 30% utilised, no core is under heavy load. Where is the bottleneck?

4

The Linux kernel does not “lock” to a core.

What’s the CPU here ?

5

i5 8400

6

Now please run the following script to enable transcoder DEBUG logging.

[chuck@lizum ~.2001]$ cat bin/set-transcoder-debug 
#!/bin/sh
Token="$(cat "/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Preferences.xml" | tail -1 | sed -e 's/.*PlexOnlineToken="//' | sed -e 's/".*//')"
curl http://127.0.0.1:32400/:/prefs/set\?TranscoderLogLevel=debug\&X-Plex-Token=$Token
echo Token=$Token
[chuck@lizum ~.2002]$

It prints your Token at the end to confirm it found it ok.

Next, please verify DEBUG logging is enabled, VERBOSE is off (Never need it)

Recreate the start of the playback (first 20 seconds)
Stop Playback
Let sit 30 seconds

Download the logs ZIP file

Attach it please.

7

Just dont ever use lg app if you need transcoding and subtitles. Buy some stick with android TV.

8

I have a brand new LG C1 OLED. I use my Nvidia Shield Pro 2019.

The WebOS app – Not the brightest bulb on the shelf :wink:

(WebOS is very restrictive API. That API doesn’t allow for much. Plex must pass the video to the API and :pray: it does the right thing)

9

How the Plex LG app handles subtitles:

  1. Enabling image based subtitles, PGS/VOBSUB, results in a video transcode.
  2. If the audio is transcoding, enabling any subtitle results in a video transcode.
  3. If the audio is direct playing, SRT (text) subtitles direct play.

With SSA/ASS subtitles:

  1. If Burn Subtitles = automatic, enabling them results in a video transcode.
  2. If Burn Subtitles = Image Formats Only, they direct play (unless audio is transcoding), but formatting information is lost

When using the Plex LG app, TrueHD audio will always transcode (*). Movies released on Blu-ray with TrueHD also include an AC-3 (Dolby Digital) version of the audio. Choose it instead to avoid transcoding.

LG dropped support for dts audio with their 2020 models. Therefore, with 2020 or later models, dts audio will transcode when using the Plex LG app. Earlier models, such as the C9 OLED, support dts, so it direct plays.


(*) No known TV supports TrueHD. It will always transcode when using the TV based Plex app, whether you’ve an LG, Samsung, Sony, Hisense, or any TV. It is a TV manufacturer limitation and applies to any app, not just Plex.

10

The problems/limitations with WebOS are now clear to me. The question now is whether it is normal that the encoding speed drops so enormously with only one tone mapping transcode with burning forced SRT subs.

I have tested all this with my workstation, my R9 5950 (32 threads) also only achieves a transcoding speed of 1.8±.

Is that really normal?

I only use WebOS in the home network, where everything runs via direct play/stream.

However, two family members have LG TVs and poor internet connections and unfortunately don’t want external devices like Shield and co.

I will add the log later today.

11

If I may add something I just figured out while assisting another user?

What I uncovered is : I still had the residual hidden preference VaapiDriver="i965" in my Preferences.xml

The encoding of the file (L5.2) is too high for the i965.

Format/Info                              : High Efficiency Video Coding
Format profile                           : Main 10@L5.2@Main
Codec ID                                 : V_MPEGH/ISO/HEVC

This caused initialization of the i965 to fail. 5.2 exceeds the upper limit of what it can do. This is a known age/design limit of the i965.

My solution:

  1. Stop Plex
  2. Remove VaapiDriver="i965" from Preferences.xml
  3. Saved the file
  4. Restarted Plex
  5. Played the file again in Plex/web

Plex/web on my system will HW transcode

Screenshot from 2021-12-14 07-41-56
Screenshot from 2021-12-14 07-41-561025×980 43.8 KB

Investigating the problem helped me resolve a problem I was also seeing on some files.

I too am new to OLED. I have been ripping some of my discs again and upgrading to the 4K UHD stream native.

Removing the hold-over VaapiDriver setting immediately put everything as it should be.

Check your Preferences.xml

Path to LG Demo file (Which is DirectStream – mkv container conversion)

12

I will test this later. Thank you very much for your efforts!

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