Plex preroll not working: every cause to check in order

A customer emailed me convinced I had sent him a broken file. The file was fine. His server was not on Plex Pass.

I have told that story for years as proof of a rule, which is that when someone says their Plex preroll is not working, nine times out of ten the file has nothing to do with it. I still believe the nine in ten. The Plex Pass half I have had to walk back a little, because when I went back through Plex's own pages this week the record turned out to be messier than the rule I had been repeating.

A Plex preroll usually fails for one of five reasons. Cinema Trailers is off in the app, the app's preroll-only option is broken, the server cannot read the path, the path field has a mistake in it or the device needs a transcode. Test with a film, one file and the web app first.

What Plex actually says about Plex Pass

The preroll arrived in August 2014 in the same release as Cinema Trailers. Plex's launch post suggests using it for "a short PSA telling your family to stop texting during the movie", which is still a better use of the slot than most, and it ends with a line saying the new trailers features are premium and require a Plex Pass subscription.

So in 2014 the answer was clear, and today it is a good deal less so.

The current Extras page puts the Plex Pass label on exactly two things, which are trailers for films in cinemas and trailers for Blu-ray releases. The Movie pre-roll video field sits on the same page with no label at all. In a 2023 thread on the Plex forum about shared users, the replies say guests do not need a subscription to see a preroll. I could not find a current official sentence that settles it for the server owner in either direction, and I looked for a while.

What the page does say, in one line that is easy to read past, is that the preroll only plays if the Cinema Trailers feature is enabled in the Plex app doing the playing. I suspect that line explains my customer better than his subscription did. Cinema Trailers is the part Plex sells. On a server without Plex Pass there are no trailers to set up, so nobody goes looking for a trailers setting inside the app, and the preroll sits behind a switch its owner has never opened. That is my reading of it. Plex has not confirmed it and I may be wrong about the mechanism.

Plex Pass is still the first thing I ask about. I have stopped telling people it is a hard requirement, because I can't show them where Plex says so.

The preroll-only option is broken in the current apps

This one is new, and in October 2026 it is the first thing I would rule out.

On 22 September 2026 a thread on the Plex forum reported that Play Pre-roll Only, the option under Settings > Player Experience > Cinema Trailers, plays nothing on iPhone, iPad and Apple TV 4K. One of the people reporting it lists server version 1.43.4.10903 and player 2026.18.0. Choose any of the Play 1 to Play 5 Before Movie options and the preroll comes back. A Plex staff member merged the duplicate reports the same day, and when I read the thread there was no fix in it and no date for one.

A thread from August describes the same failure on Android and Fire TV. There the preroll "is completely skipped" on the preroll-only option and returns, after one trailer, once the setting is changed to Play 1 before movie. The web app was reported as behaving normally. One Nvidia Shield owner in that thread got the opposite result, a trailer and no preroll, so I would not promise the workaround on every device.

Preroll-only is the option I would expect anyone with a custom intro to pick. You want your own ident and then the film, with no trailers in between. If that is your setup and the preroll vanished some time since the summer, I would bet on an app update before anything on your server.

It also loops back to Plex Pass in an awkward way. If the working setting is one that plays a trailer first, a server with no trailers to offer may have nothing to hang the preroll on. I have not been able to test that and none of the threads I read answers it.

The checks, in the order I run them

Change one thing at a time and test after each change.

1. Play a film from the beginning. Plex's documentation describes the preroll as playing before the "main feature" movie and never mentions TV episodes, so an episode proves nothing. I avoid resumed films as well, to keep the test clean. Use the same film and the same device all the way through.
2. Open the Cinema Trailers setting in the app. Plex says the label and location vary between apps and that it is often under Experience. In the current apps it is Settings > Player Experience > Cinema Trailers. If it is off, turn it on. If it is set to Play Pre-roll Only, change it to Play 1 Before Movie and start the film again. If the preroll now plays, stop here. You have hit the bug described above and the remaining steps will only cost you an evening.
3. Find the preroll field on the server. In Plex Web go to Settings, pick your server, open Extras and click Show Advanced. The field is called Movie pre-roll video. It wants the full path to the file as the server sees it, for example /media/prerolls/universal.mp4.
4. Cut the field down to one file. Plex lets you list several paths, with commas to play them in sequence or a semicolon between them to pick one at random, and its note says not to put a space before or after the separator. While you are testing, skip all of that and leave a single path in the field. I went through the multi-file syntax in how to set Plex preroll settings for multiple pre-roll files, and it is worth going back to once one file works.
5. Make sure the server can read that path. In Docker the path has to be the one inside the container, which is usually different from the one on the host. On a NAS it has to be a folder the Plex service account has permission to read, and a shared folder you made just for prerolls won't necessarily have that. The file does not need to be in a library. If you do keep it inside a movie folder, add a .plexignore file so it doesn't turn up in the library as a film.

1. Look at what the file really is. Open it in MediaInfo, which is free, and note the container, the video codec, the frame rate and the audio format. Plex's smart TV format page lists one baseline that every TV app can direct play, which is an MP4 with H.264 video at level 4.0 or lower, 1920x1080 or smaller, 30fps and AAC audio. If your preroll is 4K, or a MOV, test with a 1080p MP4 before anything else. A custom Universal studio intro from me comes as MP4 or MOV in 1080p or 4K, so for this test use the 1080p MP4.
2. Restart Plex Media Server and play the film in the web app. The August thread has the web app handling the preroll-only option correctly, which makes the browser a decent control. If the preroll plays there and not on the TV or the phone, the server side is finished and the problem is on that device.
3. Start the film on the device that fails, open the server dashboard and see whether the stream is direct playing or transcoding.

The transcode behaviour Plex doesn't document

Step 8 needs explaining, because nothing on Plex's support site will explain it for you.

In my experience Plex drops the preroll when it has to transcode it. The case I keep seeing is a 4K master on a server that is sending 1080p to a phone. The film plays, the preroll never appears and nothing in the app tells you why. I can't link an official page for this because I have never found one, and it may not hold on every client or every server version. It is still the reason a file that works on the living room TV can go missing on an iPad in the next room.

A lot of the intros I make at Priyansh Animations end up on media servers, and this is why I tell people the 4K version is the wrong one to test with. Get the 1080p MP4 playing everywhere first. Then swap in the 4K file and see which devices lose it.

If nothing has worked

If the web app plays the preroll and one device does not, go back to step 2 on that device.

If nothing plays it anywhere, I would look at the path again. Move the file into the same folder as a film that already plays, add the .plexignore, point the field at the new location and restart. That takes permissions out of the question in one go.

And if you reach the end with a file MediaInfo says is a 1080p H.264 MP4, a path the server can read and Cinema Trailers set to Play 1, add your server and player versions to the September thread. Staff were still merging reports into it when I looked.