AVPlayer 재생 상태 판단

typedef NS_ENUM(NSInteger, AVPlayerItemStatus) {
	///  
	AVPlayerItemStatusUnknown,
	///  ( )
	AVPlayerItemStatusReadyToPlay,
	///  
	AVPlayerItemStatusFailed
};

1. 우선 AVPlayer rate keyPath 감청

/*!
 @property		rate
 @abstract		Indicates the desired rate of playback; 0.0 means "paused", 1.0 indicates a desire to play at the natural rate of the current item.
 @discussion
 Setting the value of rate to 0.0 pauses playback, causing the value of timeControlStatus to change to AVPlayerTimeControlStatusPaused.
 Setting the rate to a non-zero value causes the value of timeControlStatus to become either AVPlayerTimeControlStatusWaitingToPlayAtSpecifiedRate or AVPlayerTimeControlStatusPlaying, depending on whether sufficient media data has been buffered for playback to occur and whether the player's default behavior of waiting in order to minimize stalling is permitted. See discussion of AVPlayerTimeControlStatus for more details.
 
 AVPlayer can reset the desired rate to 0.0 when a change in overall state requires playback to be halted, such as when an interruption occurs on iOS, as announced by AVAudioSession, or when the playback buffer becomes empty and playback stalls while automaticallyWaitsToMinimizeStalling is NO.

 The effective rate of playback may differ from the desired rate even while timeControlStatus is AVPlayerTimeControlStatusPlaying, if the processing algorithm in use for managing audio pitch requires quantization of playback rate. For information about quantization of rates for audio processing, see AVAudioProcessingSettings.h. You can always obtain the effective rate of playback from the currentItem's timebase; see the timebase property of AVPlayerItem.
 */
@property (nonatomic) float rate;