Some streams send clear padded data (probably
due to insufficient remaining data for encryption)

We'll only test on payload start then.

Since we can swap formats, some doesn't provide any or same values

Red over blue was against usability rules

Closed captions are in the same SEI user sections
as H264 according to the spec.

No functional changes.

In real use, there are few (typically only zero or one) listeners per
event type. In this case, the linear search through the listener groups
was actually slower than the linear search through the whole list of
listeners: it required one iteration per event type, even for event
types with no listeners.

(Note: using a hash table over the event type would make a lot more
 sense as an optimization.)

The distinction was rather vain, as the inner lock was almost never
held without the outer lock. The only case was adding an event callback
(but _not_ removing one). On the other hand, the distinction required
extra heap manipulations and memory copying for each event.

This fixes excessive (and dumb) usage of thread local variables, and
invalid use of thread cancellation.

This avoids using the buggy asynchronous event queue. This does NOT
solve other existing races and dead locks in the media list player.

As of a2ab8b27, there is always a media
player underneath the media list player.