I’ve been hitting this exact same error for a long time and finally dug into it with debug logging on. One correction to narrow it down further first: it’s not a local-vs-online distinction. I don’t have any trailers saved locally on my server at all – both “Include movie trailers from movies in my library” and “Include Cinema Trailers from new and upcoming movies in theaters” pull trailers from Plex’s online source. But only the “new and upcoming” ones ever trigger this crash; trailers for movies already in my library play fine every time, even though they’re sourced the same way. So whatever’s different is specific to that “new and upcoming” trailer category, not to local vs. remote content. Posting the root cause since the thread stalled after logs were requested.
Environment: Plex Media Server 1.43.3.10861 (macOS, Public channel, up to date). Client is Apple TV 4K running the Plex tvOS app. Trigger is specifically Settings > Server > Extras > “Include Cinema Trailers from new and upcoming movies in theaters”. Other clients (Plex Web) play the exact same trailers fine on the same server – this is Apple TV specific.
Root cause: when Apple TV requests an HLS transcode session for one of these trailers, it passes subtitles=auto and autoAdjustSubtitle=1. The transcoder then tries to resolve a subtitle stream and fails every time. From the server log, right before the crash: it does a GET to 127.0.0.1:32400/library/streams/7314643 with autoAdjustSubtitle=1, that comes back 404 from the server’s own local API, then immediately: “ERROR - Error configuring transcoder: TPU: Failed to download sub-stream to temporary file”, followed by “Terminated session … with reason Conversion failed. The transcoder failed to start up.”
I pulled that trailer’s actual metadata straight from the API (/library/metadata/) to see what stream 7314643 actually is. It’s the trailer’s 1080p H.264 video stream (streamType=“1”), sibling to an AAC audio stream (streamType=“2”) in the same Part. There is no subtitle stream (streamType=“3”) anywhere on this item at all. So the transcoder is taking a video stream’s ID and querying it through the subtitle-stream endpoint (/library/streams/, which only serves subtitle-type streams), predictably getting a 404, and treating that as a fatal transcoder configuration error instead of just skipping subtitle selection.
This isn’t a network issue either – I pulled the trailer’s actual source file straight from the CDN (video.internetvideoarchive.net, redirects to CloudFront) via curl from the server machine and it downloaded cleanly, ~101MB in about 1.5 seconds.
Things I ruled out that do NOT fix it: account-level Settings > Audio & Subtitle Settings > Auto-Select Subtitle Mode set to “Manually selected” – Apple TV still sends autoAdjustSubtitle=1 regardless, even after a full app restart. The Apple TV app’s own Settings > Subtitles category (Burn Subtitles / Override Subtitle Styles / Vertical Position) – none of those gate whether auto subtitle-selection is attempted. Server > Transcoder settings – no toggle in this PMS version to disable the auto-subtitle probe.
So this looks like a genuine bug in the transcoder’s subtitle auto-select logic specifically for the “new and upcoming” Cinema Trailers category sourced via internetvideoarchive.net: it probes a video stream’s ID through the subtitle-stream endpoint and treats the resulting 404 as fatal to the whole session instead of just continuing without a subtitle. Whatever metadata difference exists between that category and the “trailers for movies in my library” category (which never crashes) is probably the actual trigger. Happy to provide full debug logs (redacted) if that helps get eyes on it.
