Subtitles slowing down transcoding?

Server Version#: 1.27.2.5929
Player Version#: 4.76.1

Plex Media Server Logs_2022-07-10_03-43-11.zip (4.1 MB)

Hello,

I just installed the drivers for my graphics card to be able to transcode with it. Everything works perfectly fine except for one exception…

With some subtitles, the transcoding takes much longer and the CPU goes up in consumption.

With “normal” subtitles: 20% CPU no lag, ahead of reading.


Without “normal” subtitles: ~50% CPU with lag, takes a long time to transcode.

Anyone have a solution? An option to check? Subtitles not to use?


Note: Please disable verbose logging in Settings → Server_Name → General (show advanced). It adds unnecessary information to the log files. As a result, desirable information may be lost as the logs will quickly wrap.

Regarding subtitles:

From Plex Media Server.log:
Jul 10, 2022 03:38:30.882 [0x7f975afb4b38] DEBUG - [Req#b0b3/Transcode] MDE: Weathering with You (2019): selected subtitle cannot be converted to a compatible format, burning into video stream

ASS subtitles must be burned into the video stream when using Plex Web. They cannot be sent as a separate stream like the video and audio.

Subtitle burning uses the CPU, even when using hardware accelerated video transcoding. That is why the CPU utilization is higher.

Subtitle burning is also a single threaded process. So, if the video bitrate exceeds the capacity of a CPU core to burn subtitles, you may experience buffering. Example: My server has a i5-10500T CPU. It can hardware transcode multiple 4K video streams. However, it cannot burn subtitles into a single 4K transcode in real time.

Workaround: In Settings → Plex Web → Player (show advanced), change Burn Subtitles from Automatic to Only Image Formats. ASS subtitles will then direct play/direct stream, but formatting information such as position and color will be lost.

Subtitle support varies widely across the various Plex clients. ASS subtitles have poor support on most clients. Expect that enabling them will result in transcoding to burn them into the video stream.

There is work underway to add ASS support in the Android / Android TV clients, but it is only available in some preview builds (See Nvidia SHIELD/Android app SSA/ASS format anime subtitles + transcoding problems ).

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Why? AFAIK Emby support ASS subtitles on Web since a couple of years, at least in Chrome it is supported, not sure about other browsers.

Thanks a lot ! I have just modified in the parameters the engraving of the subtitles and it works really well! I’m shocked :sweat_smile:
I thought I was not in 4K so it’s going fast (normal speed).

For the moment I see no inconvenience or difference. Surely because the subtitles on this film have been placed in the base and therefore no need to modify them or what.

Thank you so much anyway! I’ll see if I can do the same on my other devices like the Nvidia Shield. Because from what I understand you are saying that it would not work? I test I will come back to you.

Thank you so much anyway !

I’ll put “solved” when I answered you!

Plex Android TV clients, including the Nvidia Shield, can direct play PGS, VOBSUB, & SRT subtitles even if the video or audio is transcoding. Direct playing of ASS subtitles is in the works. The post I linked to in my prior reply has a test build you can try if desired. You will need to sideload it to the Shield.

To watch on a PC/Mac/or Linux system, try Plex Desktop. It is a much more capable client than the web interface. I have not tried it with ASS subtitles. However, it will direct play most video and audio formats. It direct plays HDR10 video and tonemaps it if necessary. Dolby Vision formats without a HDR compatibility layer, such as Profile 5, will direct play, but the colors will be wrong. Download: https://www.plex.tv/media-server-downloads/#plex-app

Alright, I’ll look into testing Plex’s version for the Nvidia Shield if I have any issues.

And yes I know the Plex desktop app. I have them by the way, but I prefer to use the browser because I have a discord rich presence. And unfortunately it does not work with the application.
But thanks anyway ^^

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