Add subtitle offset possibility

[ErikDB87]

Changes

This pull request enables offsetting subtitles, which is a big need in my opinion. It's also a feature request with more than 150 upvotes (https://features.jellyfin.org/posts/3036/subtile-offset-on-android-tv), and it's (part of) an open issue (#2479).

Currently the changed code has a "Subtitle offset" option in the subtitle menu if the selected subtitle supports offsetting (for example srt). In that menu, there are buttons for +0.1s, -0.1s, +0.5s, -0.5s and reset. The up and down buttons on the remote add an offsett of respectively +0.1s and -0.1s, or larger offset if they are kept pressed.

The code isn't mine, but written by @pulpul-s. He (or she) deserves all the credit. But (s)he doesn't have enough time available to open up the PR. However, I think the feature is important enough to be added, so with @pulpul-s's permission, I'm opening this PR.

Code assistance

I asked GitHub's Copilot to take a look at the commit; if I'm not mistaken, my "conversation" with it can be read here: https://github.com/copilot/share/82231314-0904-80e5-9803-ec0120da2929. I also asked Claude to take a look: https://claude.ai/share/e068e7aa-def8-44d8-a726-a89708c4a4e2

One thing seems like it might be of value (in my low-value estimation):
Both agents saw some possible pitfall with assSubtitleParserFactory. Copilot wanted a change it in ExoPlayerBackend.kt, namely:

val assSubtitleParserFactory = legacySubtitleParserFactory as? AssSubtitleParserFactory ?: throw IllegalStateException("Expected AssSubtitleParserFactory when enableLibass is true")

Claude wanted to change something to VideoManager.java:
Either:

if (!(legacySubtitleParserFactory instanceof AssSubtitleParserFactory)) {
    throw new IllegalStateException("Expected AssSubtitleParserFactory");
}
AssSubtitleParserFactory assSubtitleParserFactory = (AssSubtitleParserFactory) legacySubtitleParserFactory;

or:

Or better, just don't collapse the two into one variable and keep the original code structure — legacySubtitleParserFactory is only really needed for the non-ASS branch.

Does anyone have any suggestions/feelings about this?

Of course, there might be other things that need improvement. Happy with any feedback!

Issues

#2479 (partly)

[ErikDB87]

I feel I need to add a 'help' box. Choosing + or - always confuses me. Some localization needs to be improved as well. I hope to make a new commit by Saturday.

[ErikDB87]

I feel I need to add a 'help' box. Choosing + or - always confuses me. Some localization needs to be improved as well. I hope to make a new commit by Saturday.

Done.

[ErikDB87]

Creating a help dialog box was a mistake: it was impossible to operate the buttons while the help text was visible. A help text is a much more logical approach. It also means less code, and less processing.

Also, I realized that " s" would not always be correct to indicate seconds. In Cyrillic languages, that would be " с", for example. Therefore, I went a bit further with the localization.

I uploaded a new APK as "release" in my forked repository.

[ErikDB87]

A friend told me that Claude AI is also capable of looking at an enitre repository, so I asked it to. It suggested a couple of things, which came to be these commits:

• fef82e9
• ada97e7
• 9c6f748
• 4d67f86
• e2fcb11

Some of these suggestions look logical even for me (extracting the string and style variables to their XML files and extracting the formatting function). Other suggestions go beyond me, but after Claude to explain why they're needed, my reaction was: "If you say so..." In any case, I tested the build and it works. Also, no errors seem to be logged by the Chromecast, which seem to be related to the changes of this PR.

@nielsvanvelzen, I do understand that all this AI interference is far from the ideal approach. So there surely might be a whole lot wrong with it. But there's a chance this actually leads somewhere, and I didn't want to run the risk of missing this feature. And I'm willing to make changes, obviously.

So thanks in advance for your input!

(I released my latest APK in my forked repository - for some reason the newest is below, not at the top of the list.)

[ErikDB87]

I just discovered LLM/AI guidelines... In these AI times, I acknowledge the need for such a policy, and I understand the strictness that was chosen.

I went through the commits, to check whether they don't touch anything that's not related to the intended added feature. I don't think they do. I did discover I had pushed a commit I hadn't intended to push, as the changes of that commit don't work. I removed it. (I also rebased on the updated master branch, while I was at it.)

But I see I clearly violated rule 3 of the instructions. My apologies. I'm not capable of explaining many of the changes I suggest, and the bodies of my latest commits are indeed written by Claude. My expectations of this PR being merged, therefore dropped significantly.

However, I want to stress that I had been missing this feature for a long time, and have used it a lot since I compiled the debug APK. So I hope that someone who does have enough background sees this PR and is able to submit it properly. I will probably keep using my own APK until then...