Fix initial numbering of frames in TTML to SRT converter

[TransZAllen]

What is it?

• Bugfix (user facing)
• Feature (user facing)
• Codebase improvement (dev facing)
• Meta improvement to the project (dev facing)

Description of the changes in your PR

This PR fixes the numbering in .srt subtitle files generated from YouTube streams.
Previously, numbering started at 0, which is accepted by most players but does not comply with the SubRip specification. Now numbering starts at 1, ensuring strict compliance.

• Spec reference: Wikipedia: SubRip, and it says:

Subtitles are numbered sequentially, starting at 1.

• Observed behavior: numbering started at 0.
• Tested players:
  • mpv 0.37.0 ✅ works with 0
  • VLC 3.0.20 ✅ works with 0, even -1
  • MPlayer 1.5 ✅ works with 0
  • Totem 43.0 ✅ works with 0
• Even though playback worked fine, some stricter tools may reject such files.

Why not i++ or ++i?

Every time I see i++ or ++i, I need to pause and think:

• Is it “use first, then increment” (i++) or “increment first, then use” (++i)?
• Even after I've written the code, two or three days later, when I look at the modified code, I still find myself thinking about the same issue.

To avoid this confusion, I prefer splitting the current line writeString(String.valueOf(frameIndex++)); into two lines: one to use current value of frameIndex, and the other to increment it.

Before/After Screenshots/Screen Record

• Before: Here is an example of YouTube video link (https://www.youtube.com/watch?v=Q8aPwoe_iMc), let's look at the beginning of a *.SRT file generated by NewPipe:

a51x:/storage/emulated/0/Newpipe $ cat Bear\ Family\ Searches\ for\ Water\ _\ Wild\ Mexico\ _\ BBC\ Earth-en.srt
0
00:00:00,640 --> 00:00:07,160
This mother has three young cubs just 8

1
00:00:03,840 --> 00:00:07,160
months old.

2
00:00:08,520 --> 00:00:22,899
[Music]

3
00:00:24,560 --> 00:00:29,039
It's autumn and the family needs to

4
00:00:27,119 --> 00:00:32,039
flatten up before the winter

• After: Now numbering start at 1

Fixes the following issue(s)

Fixes #12670

APK testing

The APK can be found by going to the "Checks" tab below the title. On the left pane, click on "CI", scroll down to "artifacts" and click "app" to download the zip file which contains the debug APK of this PR. You can find more info and a video demonstration on this wiki page.

Due diligence

• I read the contribution guidelines.

[TobiGr]

thanks!

[TobiGr]

I'd prefer to use this because is just a write / increment and no read. Thus there is only little room for confusion.

Suggested change

	frameIndex += 1;
	frameIndex++;

[TransZAllen]

Thanks for your suggestion.
I agree that frameIndex++ works fine here and avoids confusion.

My earlier comment about i++ / ++i was only about using them directly inside something like writeString(String.valueOf(...)), which can indeed be confusing.

Between frameIndex += 1, frameIndex++, and frameIndex = frameIndex + 1, I personally prefer += 1 because it’s very explicit and leaves no room for overthinking.

I’m fine with switching to frameIndex++ if the team prefers, but my preference would be to keep += 1 if that’s acceptable.

[TransZAllen]

Let me know if you’d like me to change it.

[Stypox]

Thanks! I'm fine with either