The idea of this feature is to have separate files for video, audio and subtitles. In that case, one can have multiple video files in different resolutions and codecs, multiple audio files also in different quality and then combine them together during playback. The result is that Plex can support different players (TVs, Web, PC, etc.) and serve them content, that is best suited for such player, without actual need of cpu expensive transcoding. Of course, muxing on the server side is needed for that. On the other hand, muxing is relatively inexpensive task. That´s what i.e. youtube is doing with their videos.
For better understanding, when using this feature, your movie folder should look similar to this:
The Movie (2020) /base folder for the movie/
- The Movie (2020).mkv /video track in the highest quality (4k HDR hevc)/
- The Movie (2020) - 1080p.mkv /video track in lower quality (1080p hevc)/
- The Movie (2020) - 720p.mkv /another video track in lower quality (720p avc)/
- The Movie (2020).en.atmos.mka /audio track for all the video versions/
- The Movie (2020).en.aac.mka /audio track for all the video versions/
- The Movie (2020).fr.dts.mka /another audio track for all the video versions/
- The Movie (2020).fr.aac.mka /another audio track for all the video versions/
- The Movie (2020).cs.ac3.mka /another audio track for all the video versions/
- The Movie (2020).cs.aac.mka /another audio track for all the video versions/
- The Movie (2020).en.srt /subtitles for all video versions/
- The Movie (2020).en.forced.srt /subtitles for all video versions/
- … similarly subtitles for other languages …
- Trailers /or any other folder for local assets/
The good thing here is, that majority of plex clients will choose the best configuration for them. So for example my PC on local network choose 4k HDR hevc video with Atmos audio track. When I open the same movie in remote web browser, the client will choose 720p avc video with aac stereo audio track, etc. So the spectator is always served with the best looking content, that his device can handle.
This feature consist of two independent parts. Firstly, it is needed to tell Plex Media Server, that for the particular movie, separated files are used. This is task for the metadata agent, that needs to be installed and enabled for the Library. You can find this metadata agent in github repository.
When you want to play the movie, Plex needs to know, that it has to mux audio and video into the stream. Default transcoder is not aware of such configuration, so it will play only the video without an audio. For that, simple script is needed, that replaces the default transcoder, checks if requested movie has sided audio, and then handover the job with all needed information to the default transcoder. Because I am operating Plex as a docker container, I've prepared my own dockerfile, that alter official Plex image with this feature. This dockerfile can be found in its github repository
Container is responsible for proper handling of sided audio when playback is requested. The core of this functionality is in the Plex Separate Parts Transcoder script, that is located in /src/Plex_Separate_Parts_Transcoder/Pex Separate Parts Transcoder.py folder.
Because I am using my personal private docker registry, all scripts here are optimized to handle that. That is also true for the configured CI/CD pipeline (.gitlab-ci.yml file). If you want to build this image, you have to alter the scripts in /build folder, or build the docker file manually.
Also it is possible to use the Plex Separate Parts Transcoder script outside of the container. But bear in mind that this script is optimized to run inside the docker container, i.e. all paths are static and according the configuration of the container. Also /tmp/scripts/prepare_image.sh script is responsible for instalation of all prerequisites that needs to be fulfilled.
All scripts in this repository are targeted for Linux. Eventhough the idea of this feature can be used also for Plex Media Server running on Windows platform, the implementation is not ready to support that.
This feature is proven to be working on Plex Web Client, Plex Windows Client and Plex iOS Client. Others haven't been tested.
Also there is an issue with Plex for Kodi addon. This addon completely fails to cooperate with this feature and results in the Playback failure when used. Probably, this will be also valid for Roku client, because of the similarities in the source codes.
This feature is provided as is without any support and responsibility. It is not mature enough to be widely used. So use it only on your own risk and be 100 % sure that you know what you are doing. Unfortunately, expected behavior of this feature is reachable only with direct altering of Plex database and replacing core components of Plex Media Server - therefore it is not how Plex is intendend to be used.
Please note that this Github repositories are only mirrors of my private personal git repositories, that I am using and developing against.
The idea for this feature is based on the job of Saoneth. Also, I've reused and extend some of his scripts. You can find his implematation in its github repository