Inconsistencies between various (GStreamer/AVFoundation) video player implementations

I've just cross compiled an application which is repeatedly loading videos. There were some smaller differences which caused some troubles for me. I'm not saying one implementation is right, the other one is wrong. But to know that all behave the same would be supercool.

For example:

• Play Flag: setPaused(true) sets the isPlaying() flag to false in AVFoundationPlayer, but does not touch the isPlaying()flag in the gStreamer implementation.
• Rewind: after loadAsync(), the currentFrame()is set to 0 in AVFoundation, but left untouched in the gStreamer implementation (i.e. where the clip before ended). Probably also for load(), but I didn't check.

Missing Callbacks:

With all players more and more loading clips async, I guess a simple event/callback system will be necessary. The only option right now is to check in the main loop if a clip is loaded or playing or paused, which is a little bit annoying and sometimes quite faulty.

Start by comparing the AVFoundationPlayer and GStreamer implementations around setPaused(true), isPlaying(), loadAsync(), load(), and currentFrame(). Define consistent playback and rewind behavior, then determine the scope of the proposed event/callback system; done means the players expose matching state behavior and a clear notification mechanism for loading, playing, and pausing.