Transcoding Fails when subtitle track is selected

Plex Media Server NAS & Devices
1

Server Version#: 1.41.7.9749-ce0b45d6e
Player Version#: app.plex.tv (edge browser)

Whenever I select a subtitle track, playback fails. I’m running PMS on an ASUSTOR 5402T.

  • Verified filesystem permissions
  • Intro/credit detection works fine
  • Media libraries are updated to the new agents, metadata refreshed
  • No SQLite DB errors in the logs
  • Tried with both disabled and enabled hardware acceleration
  • Not using a custom transcoder temporary directory

I don’t know what else to try; thank you in advance!
Plex Media Server Logs_2025-05-19_14-34-12.zip (2.3 MB)

2

Can you please update to the latest Beta and retest. There was a bug in the earlier Beta version that was causing the DB to expand. This may not be the root cause but lets at least remove it from the equation.

Also seeing Errors calling out a possible double NAT environment. Please check out this support article for some possible assistance:

3

Updated using the beta release channel. Transcoder still failed, new set of logs attached. I’m aware of the double NAT, it’s not a major concern right now.
Plex Media Server Logs_2025-05-19_15-27-03.zip (2.0 MB)

4

Just wanted to chime in, I took an having the issue with the transcoding sub error like you described. But my server is hosted on a windows 11 pro system.

Also worth note: I am not, and never was on beta. This issue also only started this weekend for me.

It happens no matter the device I playback from or if it’s LAN or WAN playback

5

Any other ideas?

6

@PIPXIll you’ll need to share you PMS logs. Make sure to enable Debug logging.

@wipeout630 Still investigating. This does initially appear to be networking related as previous users with the same Error message reported was identified as having a bad network configuration (reverse proxy). I would advise to resolve the double NAT issue and see if the issue is resolved. Will continue investigating.

Also, make sure to install the latest update, which is currently 1.41.7.9799.

7

@Atomatth Here they are. hope this helps fix things up for anyone dealing with the issue.
Plex Media Server Logs_2025-05-22_15-21-45.zip (4.7 MB)

1 Like
8

I resolved the double NAT and confirmed PMS is fully available outside my network. Transcoding still failed. New set of logs attached but still shows the same error: “Error configuring transcoder: TPU: Failed to download sub-stream to temporary file”

I updated PMS to 1.41.7.9823.

Plex Media Server Logs_2025-05-27_21-55-25.zip (1.0 MB)

9

I think I figured it out! By default, PMS is searching for subtitles instead of using the local files. I manually uploaded the .srt file to the episode and it started transcoding and playback worked perfectly.

I need to disable the default web search, it was pulling a bad file. Secondly, I need to fix the local .srt file naming convention. I’m also adding OpenSubtitles.org as a fallback.

10

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