bogsen/fix-plex-hdr-subtitles.md

## fix-plex-hdr-subtitles.md

      
    Raw
  

              fix-plex-hdr-subtitles.md
            
          
    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"
	#!/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"