External SRT subtitles desync after seeking during transcode

Plex Media Server
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1

Environment

  • Server version: 1.43.3.10828
  • OS: Arch Linux (bare metal, not Docker)
  • Clients: Plex for Linux, Plex for LG TV

Problem

External SRT subtitles go completely out of sync after the first seek when the video is being transcoded from 4K to 1080p. The subtitles never recover, they remain desynced for the rest of playback, sometimes even disappearing

This is 100% reproducible across multiple clients (Linux desktop app, LG TV app).

Steps to reproduce

  1. Play a 4K HEVC movie with an external SRT subtitle selected.
  2. Force transcode to 1080p.
  3. Let the movie play normally for a minute, subtitles are in sync.
  4. Seek/skip forward or backward to any position.
  5. Subtitles are now completely out of sync.

Observations

  • External SRT + transcode + seek = desync, every time, on first seek
  • External SRT + direct play + seek = fine, no desync
  • External SRT + transcode + no seeking = fine, subtitles stay in sync if you never seek

This points to a bug in how the transcoder re-aligns external SRT timestamps when starting a new transcode session after a seek.

Expected behavior

External SRT subtitles should remain in sync with transcoded video after seeking, matching the behavior of embedded SRT subtitles.

2

The external SRT files were truncated or for the wrong release. Several only covered 30-50% of the movie duration, so subtitles disappeared after seeking past the point where the SRT ended. Movies with correct SRT files worked fine, including during transcoding and seeking. Deleted the broken files, problem solved. Apologies for the false report!