Allow bitrate level increase after low fps

When the fps to dropped frame ratio is poor, the video quality level is dropped per the capLevelonFPSDrop config. However, there is no forgiveness. Once the level drops due to poor FPS, the level will never increase again. In a live stream with other activity on the page (such as chat), there may be transient FPS issues that cause the level to drop, but then the level is never able to go back up for the remainder of the show.

I would like to request a configurable amount of time after an FPS drop that a higher level will be attempted again. For example, start at level 5, low FPS for 5 seconds and the level drops to level 4, then 15 seconds later, level 4 is attempted again.

Some exponential back off on retrying a higher level would also be nice. For example, start at level 5, low FPS causes the level to drop to 4, then 10 seconds later it tries level 5 again, but that has low FPS again so the level drops to 4, then 20 seconds later it tries level 5 for a third time, and so on.

No source file, test, or entry point is identified in the issue. Start by locating the capLevelonFPSDrop implementation and its quality-level selection logic. Done means a configurable retry delay can restore a higher level after an FPS-triggered drop, with the requested backoff behavior covered by tests.

Written by the indexing model from the issue text.