Optimizing Plex media files

Many devices do not support Direct Play functionality when playing media files from your Plex server. In such cases, Plex will transcode files during playback, in other words: convert to a format which the device (e.g. a TV) can handle.

On this page, under 'Specific Model Differences', you will find an overview of TVs with DirectPlay support for Full-HD files. Does your TV support H.264 and H.265 MKV content according to this page? Then, no transcoding is required for MKV files and your CPU is not loaded at all.

Do you prefer not having to transcode media at all during playback and is your TV not in the list of supported models above? Then, you can achieve this by either using MP4 files or optimizing your media in advance (i.e. converting to MP4) or connecting a (hardware) media player with Plex Direct Play support to your TV, such as a Roku player. In this article, we show you how to:

• Automatically optimizes media files for Plex, so you don't have to transcode the entire video and audio stream live.
• Manually optimize media files.

The impact of transcoding MKV files live

The impact of MKV files which you play on devices that do not support Direct Play on your CPU load is as follows:

• Are there x265 MKV files on your VPS? Then, Plex will transcode the files as a whole (video and audio) during playback. This process is CPU intensive: if one person watches an x265 MKV stream in 1080p from your Plex server, this already taxes two full CPU cores of your VPS.
   
• Are there x264 MKV files on your server? Plex will then only transcode the audio during streaming. This will require no more than 10-20% of a single CPU core.

Automatically optimize media files

Optimizing your media is actually a pre-transcode; media is converted to an mp4 format which your TV (or another device) can handle. If you use the optimized version, your CPU is no longer taxed while watching media, only your network is. In case of an X4, for example, this means the difference between a maximum of one simultaneous user or many simultaneous users.

Step 1

Connect to your VPS via SSH or the VPS console in your control panel.

Step 2

There is a bug in Plex at the time of writing in which not all variables are correctly configured for certain command-line commands (this is especially relevant if you want to scan your media library via command-line, for example). You solve this with the commands:

export LD_LIBRARY_PATH=/usr/lib/plexmediaserver:/usr/lib/plexmediaserver/lib
export PLEX_MEDIA_SERVER_

• /usr/lib/plexmediaserver is set by default and preserves backward compatibility, /usr/lib/plexmediaserver/lib is where the library is actually located.

Step 3

Create a shell script; the location and name do not matter, as long as you use the same for the next steps in this article, for example:

nano /usr/local/bin/plex.sh

Step 4

Add the code below to the file, making the following adjustments:

• Adjust the value of the plex folder variable (/mnt/bigstorage/plex-media) to the folder on your VPS in which the .mkv files are located.
• The script has been set to delete the original file. If you would like to test the MP4 file before deleting the file, remove rm -f "$ file", or replace it with, for example, mv "$ file" /tmp/ to place the file in the /tmp folder. The /tmp folder is automatically emptied after every reboot of your server (you can also adjust when /tmp is emptied).

#!/bin/bash
plexfolder=/mnt/bigstorage/plex-media/

# Counts the amount of .MKV files
i=$(find "$plexfolder" -name *.mkv -printf '.' | wc -c)

# Retrieves the names of each MKV file and its parent folder. 
# The files are then transcoded, and the original removed.
for i in $(seq 1 1 $i)
do
   file=$(find "$plexfolder" -name *.mkv | head -n 1)
   filename=$(find "$plexfolder" -name *.mkv -printf "%f\n" | head -n 1 | grep -oP '.*(?=[.])')
   folder=$(find "$plexfolder" -name *.mkv -printf '%h\n' | head -n 1)
   output="$folder/$filename.mp4"
   ffmpeg -i "$file" -vcodec libx264 -crf 19 -maxrate 3M -bufsize 6M -x264opts cabac=0:8x8dct=1:bframes=0:subme=0:me_range=4:rc_lookahead=10:me=dia:no_chroma_me:8x8dct=0:partitions=none -map 0:0 -sn -acodec libfdk_aac -strict -2 -cutoff 15000 -ac 2 -ab 217k -map 0:1 -map 0:2 "$output"
   rm -f "$file"
done

Explanation

• The variable i is the total number of MKV files in the folder which you set as the variable plex folder.
• The for loop repeats itself until no more MKV files are present (the number of times is determined by the “i" variable).
• file is the name of the 1st MKV file including folder (e.g. /mnt/bigstorage/plex-media/video/example.mkv.
• filename is the name of the file excluding folder and extension (e.g. example).
• folder is the folder in which the file is located (e.g. /mnt/bigstorage/plex-media/video).
• output merges the folder with the filename and adds the extension .mp4.
• ffmpeg this command converts the mkv file to an mp4 file, with similar specifications to the optimize function in Plex itself. An important point is that -maxrate 3M limits the bitrate of the output file to 3000. Do you want a higher bitrate? Then, adjust the value to, for example, 6M for 6000 and -buffsize to 12M. The value you set here also determines the required upload speed of your server for the specific file, and the required download speed for the device on which you play it.
• rm -f "$ file" deletes the original file. 

Step 5

The script does not yet have export rights. You adjust this with the command:

chmod 755 /usr/local/bin/plex.sh

This gives all users read and execute rights and full rights to the user with whom you create the file.

Step 6

Run the script once and wait until it is done. Keep in mind that if you have 100GB of media, for example, this can easily take 3-4 days. If you use an X4 and want to be able to use your VPS in the meantime, it is advisable to temporarily add one or two extra CPU cores to your VPS.

/usr/local/bin/plex.sh

Step 7

To further completely automate the process, create a cronjob to run the script again every day. To do this, create a log file, a lock file (see the explanation in step 9) and the cron job with:

touch /tmp/plex_transcode.lock
touch /var/log/plex_transcode.log
crontab -u plex -e

Step 8

There is no crontab for the user Plex yet, so, this is newly created.Press 'i' to start the insert mode and paste the following lines: 

/user/local/bin/plex.sh
plex_transcode.log

Press 'esc' > :wq! consecutively to save the changes and close crontab.

Explanation

• SHELL=/bin/bash: run commands in the script with bash.
   
• HOME=: the location of the home directory
   
• PATH=: By default, Cron defines as PATH variable /usr/bin:/usr/sbin: With this line, you extend it to include /usr/local/sbin, /usr/local/bin, /sbin and /bin .
   
• 0 3 * * * * etc: Every day, the script is started at 3:00 in the morning by the user 'plex'. If necessary, adjust the 3 if you want the script to be executed earlier or later, or use * * /1 * * * for example to have it executed every hour.
   
• The addition flock-n /tmp/plex.lock places a lock on your script provided it is already active. Is the script still transcoding? Then, the next day, a new attempt will be made to execute the script. Instead of -n you can also use -w <seconds>, for example -w 7200 to try again two hours later.
   
• The output of the script is written to /var/log/plex_transcode.log

Optimize media manually

Do you prefer to manually optimize your media files? In the Plex web interface, go to the relevant folder or file that you want to optimize and click the colon at the bottom right of the thumbnail and select 'optimize'. 

You will see a screen with some options. For example, choose whether you want to optimize files for a TV, or for a mobile, how many files you want to optimize at one time, and then click 'optimize' at the bottom right.

Should you have any questions left regarding this article, do not hesitate to contact our support department. You can reach them via the ‘Contact Us’ button at the bottom of this page.