Plex subtitles out of sync

What Plex does on its own

Auto-Sync Subtitles splits the work: the server analyses the audio for voice activity, and the client shifts the subtitle rendering to match. Your client generally enables it by itself, and there is an Auto-Sync Subtitles tick box in the playback settings if it has not.

Four things all have to be true:

• A Plex Pass on the server admin account.
• A Plex Pass on the account actually watching, on that device.
• Media analysis and voice activity detection enabled in server settings.
• An external SRT, or a subtitle Plex fetched from OpenSubtitles. Embedded tracks are out of scope.

Voice activity detection is also not available on every server platform. FreeBSD, the Nvidia Shield and several NAS builds cannot run it, so the feature is simply absent there no matter what you are subscribed to. That is worth checking before assuming something is broken.

The manual offset

Separately from Auto-Sync, most Plex clients expose a subtitle offset in the playback settings, adjustable in 50 millisecond steps — the same increment VLC uses, and the same one the arrow keys use here. If you already know your file is two seconds early, this is the quickest route to watching it tonight.

Where each one stops

Neither correction is in the file

This is the part that catches people out later rather than tonight. Both the offset and the Auto-Sync result are applied at playback, by Plex. The.srt on disk is untouched.

So the moment the file leaves that context — copied to a phone, opened in VLC, handed to someone else, played through a client that does not support the feature — it is out of sync again by exactly the original amount. If the file is something you keep rather than something you watch once, correcting the file itself is the version that lasts.

When the error grows rather than staying constant

An offset is one number added to every line, so it cannot absorb an error that increases as the film plays. If the opening is right and the closing credits are minutes out, no offset setting will hold, and you will find yourself nudging it again every twenty minutes.

That is a frame-rate mismatch, almost always 25 fps subtitles against a 23.976 fps release. The timestamps have to be rescaled, which is a different operation from shifting —converting 25 fps to 23.976 covers it, anddrift over time covers how to measure the ratio when you do not know the rates.

When Plex will not load the file at all

Before assuming a timing problem, confirm Plex is reading the subtitle you think it is. The basename has to match the video exactly, and Plex reads a language code from the end of the filename, soFilm.2019.en.srt is selected as English whereFilm.2019.srt may appear as Unknown. TheMKV guide has the full naming convention, including forced and SDH variants.

If the name is right and it still does not appear, the usual causes are that the library has not been rescanned since you added the file, or that local media assets are disabled for that library in its agent settings. Neither has anything to do with the subtitle itself.

If the characters are wrong rather than the timing

Question marks or accented gibberish where other letters belong is an encoding problem, and no amount of syncing touches it. Seesubtitles showing question marks.