AV subtitle durations sometimes handled incorrectly

[Jim Stichnoth <stichnot@…>]

​https://docs.google.com/leaf?id=0BxETmfuHvGPQOWQ0YzZkZGUtOGNjNy00MzI3LTk3ZWQtYjg5N2I5NjQ0MDNj&sort=name&layout=list&num=50

This is a 100 MB sample from a children's DVD with a "read-along" feature implemented in terms of AV subtitles. The appearance of this feature is that individual words in the subtitle change color as they are spoken. The experience in myth is pretty bad, as the subtitles flash on and off quickly instead of displaying smoothly as they do in vlc. It appears the author of this DVD is using zero-duration subtitles to mean infinite duration (or until the next subtitle is to be displayed). The attached patch changes zero duration to be 10 seconds, which makes the sample display nicely, even if it's not necessarily the best solution.

The second issue is probably related. If you pause while a subtitle is displayed, it is still erased after its duration elapses, even though playback is paused. This is because of the way m_expireTimes is used. I didn't test, but I suspect the subtitle durations do not respect timestretch.

[markk]

Jim - is that link correct? It's not working for me here. thanks.

[markk]

(In [25670]) If an AVSubtitle has a duration of exactly zero, bump the display time to 1 minute - which should cover most use cases.

Also filter out some unnecessary logging when AVSubtitle display is only fractionally late.

Refs #8781

[markk]

(In [25674]) Use the frame timecode to expire AV subtitles.

The old time based approach didn't account for changes to playback speed such as pause and timestretch. Using the timecode also brings AV subtitles in line with the other types of subtitle.

Closes #8781

[Jim Stichnoth <stichnot@…>]

Some logic in [25670] is wrong. The v2 patch fixes it.

[markk]

(In [25756]) Fix zero duration AVSubtitle following r25670.

Closes #8781 - thanks to Jim