"Seek over gap" feature seeks to first subtitle when subs are enabled

[joeyparrish]

Have you read the FAQ and checked for duplicate open issues?
Yes

If the problem is related to FairPlay, have you read the tutorial?

N/A

What version of Shaka Player are you using?

4.9.2 (CAF)

Can you reproduce the issue with our latest release version?
Yes

Can you reproduce the issue with the latest code from main?
Yes

Are you using the demo app or your own custom app?
Custom app

If custom app, can you reproduce the issue using our demo app?
Didn't try in this case, because I have already found the root cause

What browser and OS are you using?
Chromecast

For embedded devices (smart TVs, etc.), what model and firmware version are you using?
Chromecast w/ Google TV (Android-based, latest production firmware)

What are the manifest and license server URIs?

Using a partner's receiver app

What configuration are you using? What is the output of player.getConfiguration()?

Default

What did you do?

Start content with subtitles enabled

What did you expect to happen?
Content plays from 0, including pre-roll ads

What actually happened?

Content plays from the first subtitle, which leads to skipping the pre-roll ad

Are you planning send a PR to fix it?
Yes

[joeyparrish]

I figured out the root cause, and I have a fix that does not require reverting the PR that introduced it (#6340).

The logic introduced in the PR looks roughly like this:

if (!live &&
    paused &&
    startTimeOfFirstSegment > 0 &&
    playhead < startTimeOfFirstSegment) {
  skipAhead();
}

The problem is that the start time of the first segment of text is non-zero. Seeking over an initial gap fixed real content issues, but it makes no sense to seek over a gap in text, so we should simply exclude text segments from this check.

[joeyparrish]

The bug affects v4.6.16-18, v4.7.12-15, v4.8.0-20, v4.9.0-26, v4.10.0-16, and v4.11.0-2.

[joeyparrish]

v4.6, v4.7, and v4.8 are no longer maintained and will not get a cherry-picked fix.