What happened to chapters in ATV4?

Is there a fix/work-around?

Yes. Set/designate a "Language" setting for the Chapter text track. Normally this would be the same as your audio track(s).

1- are you saying I'd have to re-encode every video?

No.

2- I've never even seen a language setting for chapter text track in handbreak.

I don't believe they currently have such an option. Output currently looks like this:

When I change the Chapter Track language ID from "Unknown" to "English" (my default language) like this:

Then the TV4 displays chapter options in the "Info" window which can be selected by the user. This workflow does not require re-encoding the file—only changing the language ID value associated with the "Chapter Track" of your HandBrake files. All tracks have language ID values but previous versions of the TV IOS did not check the "Chapter Track" language ID as TV4 tvOS now does. And, while tvOS does not appear to currently check the "Video Track" language ID, I'm changing mine when I reset the "Chapter Track" in case Apple decides to make similar changes sometime in the future.

Can you elaborate on this: ie how to do it... (I'm a window user, if that makes a difference)

As a Mac user, I'm not familiar with what utilities might be available to you but believe one was mentioned in a similar topic on this forum. QT 7 Pro can probably do this in the "Properties" window as seen here for the Mac version:

However, this would probably create a new MOV file which would be a pain. Atom editor utilities can also do this but may force you to input the language ID code manually as seen here for Atom Inspector utility for the Mac:

I personally use a Mac GUI utility called Subler—as seen in my previous response since using the "Language" pop-up opt is so much easier. In addition, the utility was designed specifically to "mux" the changes back into the original M4V file container like the atom-level utilities. (I believe this is the same strategy used by the Windows utility. Unfortunately, I don't remember its name and after searching for an hour could not locate the discussion in which it was mentioned.)

UUseful info - thanks John! I have found and confirmed the update works. Do you know of any way to mass edit? I have thousands of videos...

also, I have found a handful that have no chapter info? At that point is it best to just "create a chapter every..." Or is there an import I can use?

thanks again! I wonder why the new Apple TV doesn't register the "unknown" language for chapter files? Easy but tedious fix...

Do you know of any way to mass edit?

No, not at this time.

At that point is it best to just "create a chapter every..." Or is there an import I can use?

This is up to the individual user and particular workflow requirements. I normally use an app like Road Movie to add custom chapter markers. It can add and edit chapter markers at user selected points while previewing video content, automatically add chapter markers at fixed intervals like Subler, and import and apply or export chapter markers to/from text files. However, unlike Subler which adds the changes back to the original M4V file, Road Movie creates a separate MP4 file using its own "Pass Through" option to mux the chapter track with the original audio and video data. On the other hand, you can use Road Movie to create and export a "custom" chapter track for your original file and then use Subler to add the newly created chapter track to the original M4V file which handles all of my "add-on" chaptering needs.