Fix Plex transcoding HDR videos very slowly when burning subtitles in at the same time

fix-plex-hdr-subtitles.md

This workaround should no longer be necessary with newer Plex versions: https://forums.plex.tv/t/subtitle-burn-in-improvement-test-build/884481

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Old content left here for reference:

What?

For some reason, although Plex supports hardware-accelerated HDR tone mapping, Plex decides not to use it when subtitles need to be burned in. This results in extremely slow transcoding on hardware that should be able to keep up using hardware acceleration. I've noticed this issue on my server with Intel QuickSync, and this fix is made specifically for that case.

Before the fix, the SW tone mapping was only able to do 6-7 fps on a i5 7400T for an HDR 4K->1080p transcode. With the fix, that same transcode happens with HW tone mapping, and goes up to 82 fps. Even for HDR 4K->4K, this CPU is able to do 35 fps using QuickSync, thus keeping up with at least one video stream.

How do I fix this?

By wrapping "Plex Transcoder" with a script which replaces the software tone mapping with hardware tone mapping.

A filter configuration for software tone mapping looks like this: [0:0]scale=w=1920:h=1080:force_divisible_by=4[0];[0]format=p010,tonemap=mobius[1];[1]format=pix_fmts=nv12[2];[2]inlineass=font_scale=1.000000:font_path=/usr/lib/plexmediaserver/...[3];[3]hwupload[4]

A filter configuration for hardware tone mapping looks like this: [0:0]scale_vaapi=w=1920:h=1080:format=p010[0];[0]hwmap=derive_device=opencl,tonemap_opencl=tonemap=mobius:format=nv12:m=bt709:p=bt709:r=tv,hwdownload[1];[1]format=pix_fmts=nv12[2];[2]inlineass=font_scale=1.000000:font_path=/usr/lib/plexmediaserver/...[3];[3]hwupload[4]

For the linuxserver.io Plex docker image, I've attached a script which can be added into custom-cont-init.d (by using a bind mount) that fixes the issue described here. Use at your own risk, it may cause issues in other transcoding scenarios which I didn't test yet.

fix-plex-hdr-subtitles.sh

#!/bin/bash -ex
cd /usr/lib/plexmediaserver
if [ ! -f "Plex Transcoder.before-hdr-subtitles-fix" ]; then
  mv "Plex Transcoder" "Plex Transcoder.before-hdr-subtitles-fix"
fi
cat >"Plex Transcoder" <<"EOF"
#!/usr/bin/env -S perl -l
use warnings;
use strict;
my $found = 0;
for my $arg (@ARGV) {
  my $updated = $arg =~ s/(\[[\w:]+\])scale=(w=\d+:h=\d+)[^[]+(\[[\w:]+\]);\3format=p010,tonemap=(\w+)(\[[\w:]+\]);/$1scale_vaapi=$2:format=p010$3;$3hwmap=derive_device=opencl,tonemap_opencl=tonemap=$4:format=nv12:m=bt709:p=bt709:r=tv,hwdownload,format=pix_fmts=nv12$5;/r;
  if ($updated ne $arg) {
    print("Enabled HW tone mapping:");
    print("Original: $arg");
    print("Updated:  $updated");
    $arg = $updated;
    $found = 1;
    next;
  }
  $updated = $arg =~ s/(\[[\w:]+\])scale=(w=\d+:h=\d+)[^,[]+/$1hwupload,scale_vaapi=$2,hwdownload/r;
  if ($updated ne $arg) {
    print("Enabled HW scaling:");
    print("Original: $arg");
    print("Updated:  $updated");
    $arg = $updated;
    $found = 1;
    next;
  }
}
if ($found) {
  if (!defined $ENV{OCL_ICD_VENDORS}) {
    $ENV{OCL_ICD_VENDORS} = '/config/Library/Application Support/Plex Media Server/Cache/cl-icds-linux-x86_64';
    $ENV{cl_cache_dir} = '/config/Library/Application Support/Plex Media Server/Cache/Shaders/icr-97-linux-x86_64/';
  }
  unshift(@ARGV, "-hwaccel_output_format:0", "vaapi");
}
unshift(@ARGV, "/usr/lib/plexmediaserver/Plex Transcoder.before-hdr-subtitles-fix");
exec { $ARGV[0] } @ARGV;
EOF
chmod +x "Plex Transcoder"

Can Plex not introduce some kind of pool where people donate to a specific task? I would vote with my money to prioritise this feature over any mapping fixes personally.

I wanted to put some perspective on why Plex had to change priorities as some may not be aware.

Linux kernel 6.8 broke HDR tonemapping for Intel encoding accidentally. And this bug was shipped with ubuntu 24.04 LTS release and won't have the fix until 24.04.1 in probably 6 months to a year. Non-LTS releases can update to the fixed kernel already, but LTS channel is stuck with it.

This sent everyone in a panic, because it means everyone was updating and unable to use Plex HDR content without issues.

Sadly, it makes sense that Plex has to change priorities... The subtitle burnin can be avoided by turning off subtitles or using non-image based subtitles like srt. There are many ways around that issue.

Many paying customers could not get around their vm hosts with Intel hardware being unable to display tonemapped content.

Unfortunately, it's a better business decision to fix the issue users can't work around first, especially when they know there's not going to be a fix by Ubuntu for months.

I am fully aware that it is a priority and understand it, but my suggestion is relating to perhaps Plex having a feature 'vote' where people could pool towards a target feature which would then allow for additional development for that said feature.

People do it on here quite often with large repos that are depended on for lots of people. I personally would put £100 GBP towards this, which may on its own be nothing but if a pool of other people that want to stay with Plex put together it should add up to enough for Plex to warrant additional development on the feature. (and others moving forward).

I ran this script inside the official PMS docker container, but plex just dies as soon as it tries to transcode

@tortxoFFoxtrot - Migrate to Jellyfin or wait for the support to eventually be added.

@chrisdecker08 @Drakonas - has this had any attention or discussion Plex side between the last update a month ago and now?

@tortxoFFoxtrot - Migrate to Jellyfin or wait for the support to eventually be added.

@chrisdecker08 @Drakonas - has this had any attention or discussion Plex side between the last update a month ago and now?

Am I doing something wrong or is it known not to work in the official docker?

I don't know, I couldn't get it to work entirely, it broke some transcoding and improved others. Ended up not using it because of that. Waiting on Plex adding it but am also running Jellyfin next to it for this.... It is lightening quick at transcoding including subs.

I don't know, I couldn't get it to work entirely, it broke some transcoding and improved others. Ended up not using it because of that. Waiting on Plex adding it but am also running Jellyfin next to it for this.... It is lightening quick at transcoding including subs.

Eh I have family members who remote in to use my plex, switching to jellyfin is a hassle all around

I know, same boat, PITA. Hence why I am a bit miffed that this is put off priority wise consistently, although I do understand other work takes priority.

The only REAL reason to not entirely switch to Jellyfin is client playback for things like VIDAA and having to sideload on Samsungs etc. Once it is setup though it actually is faster to use all round in my opinion, especially for transcoding... that said, I would like to just stick with Plex but this is making it very very difficult.

Yea so the Hisense VIDAA TV is actually the TV causing the issue where subtitles get burnt in on transcode, even my iPhone is just direct stream the SRT on transcode, but the VIDAA seems to suck.

I ran this script inside the official PMS docker container, but plex just dies as soon as it tries to transcode

This is for the Linux server Plex container. https://github.com/linuxserver/docker-plex

For the linuxserver.io Plex docker image, I've attached a script which can be added into custom-cont-init.d (by using a bind mount)

FYI, I have incorporated this functionality into the PMS test build found here, please come give it a try and let me know if everything works ok.

great thanks! could you add a docker image if possible?

…

On Tue, 6 Aug 2024 at 10:23 AM, chrisdecker08 ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ FYI, I have incorporated this functionality into the PMS test build found here <https://forums.plex.tv/t/subtitle-burn-in-improvement-test-build/884481/2>, please come give it a try and let me know if everything works ok. — Reply to this email directly, view it on GitHub <https://gist.github.com/bogsen/37cbad60f6c10cdaddf3b07a56e06147#gistcomment-5144831> or unsubscribe <https://github.com/notifications/unsubscribe-auth/AEB3SF4NAKWLLAPK73ZZ5UDZQAJOZBFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDUOJ2WLJDOMFWWLO3UNBZGKYLEL5YGC4TUNFRWS4DBNZ2F6YLDORUXM2LUPGBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVEYTEMJRGE4TQOJZU52HE2LHM5SXFJTDOJSWC5DF> . You are receiving this email because you commented on the thread. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> .

Unfortunately, we do not generate docker images for test builds. You'll have to wait until the work lands in beta.

FYI, I have incorporated this functionality into the PMS test build found here, please come give it a try and let me know if everything works ok.

I just installed it and gave a quick pre-test before and after of both actual real world performance issue, htop and intel_gpu_top, and after installing there is literally a 10 times performance boost. It's gone from not being able to do one 4k HDR -> 1080p SDR with PGS burnt to maybe doing 3-4?

Awesome. Thank YOU!!!

Thanks @chrisdecker08, nice to see this finally land! (I'm not currently using Plex so I can't test, but I've added a link to your forum post in the gist.)