ijkplayer源码阅读02-播放协议
概述
ijkplayer 是Bilibili开发并开源的轻量级视频播放器，支持本地网络视频播放以及流媒体播放，支持iOS和Android平台。ijkplayer基于 FFmpeg 是一套可以用来记录、转换数字音频、视频，并能将其转化为流的开源计算机程序。 FFmpeg 采用LGPL或GPL许可证，提供了录制、转换以及流化音视频的完整解决方案，包括了领先的音、视频编码库libavcodec等。
特性
platform | version | CPU| video-output|audio-output|hw-decoder
:---:|:---:|:---:|:---:|:---:
iOS | iOS 7.0+ | armv7, arm64, i386, x86_64|OpenGL ES 2.0|AudioQueue, AudioUnit|VideoToolbox (iOS 8+)
Android | API 9+ | ARMv7a, ARM64v8a, x86 |NativeWindow, OpenGL ES 2.0|AudioTrack, OpenSL ES|MediaCodec (API 16+, Android 4.1+)
IJKMediaPlayback
IJKMediaPlayback是 ijkplayer 中最重要的协议。由于 ijkplayer 中有几种不同类型的播放器实现（如：基于AVPlayer实现的IJKAVMoviePlayerController，基于MPMoviePlayerController实现的IJKMPMoviePlayerController，基于FFmpeg实现的IJKFFMoviePlayerController）。为了统一播放行为，ijkplayer 使用了一套基本协议，使每种底层不同实现的播放器能为使用者提供统一的接口。
@protocol IJKMediaPlayback <NSObject>
- (void)prepareToPlay;
- (void)play;
- (void)pause;
- (void)stop;
- (BOOL)isPlaying;
- (void)shutdown;
- (void)setPauseInBackground:(BOOL)pause;
// 视频画面
@property(nonatomic, readonly) UIView *view;
// 重播次数
@property(nonatomic) NSTimeInterval currentPlaybackTime;
@property(nonatomic, readonly) NSTimeInterval duration;
@property(nonatomic, readonly) NSTimeInterval playableDuration;
@property(nonatomic, readonly) NSInteger bufferingProgress;
@property(nonatomic, readonly) BOOL isPreparedToPlay;
@property(nonatomic, readonly) IJKMPMoviePlaybackState playbackState;
// 加载状态
@property(nonatomic, readonly) IJKMPMovieLoadState loadState;
@property(nonatomic, readonly) int64_t numberOfBytesTransferred;
// 视频原始尺寸
@property(nonatomic, readonly) CGSize naturalSize;
// 画面填充模式
@property(nonatomic) IJKMPMovieScalingMode scalingMode;
@property(nonatomic) BOOL shouldAutoplay;
@property (nonatomic) BOOL allowsMediaAirPlay;
@property (nonatomic) BOOL isDanmakuMediaAirPlay;
@property (nonatomic, readonly) BOOL airPlayMediaActive;
@property (nonatomic) float playbackRate;
@property (nonatomic) float playbackVolume;
// 视频截图
- (UIImage *)thumbnailImageAtCurrentTime;
#pragma mark Notifications
#ifdef __cplusplus
#define IJK_EXTERN extern "C" __attribute__((visibility ("default")))
#else
#define IJK_EXTERN extern __attribute__((visibility ("default")))
#endif
// -----------------------------------------------------------------------------
// MPMediaPlayback.h
// Posted when the prepared state changes of an object conforming to the MPMediaPlayback protocol changes.
// This supersedes MPMoviePlayerContentPreloadDidFinishNotification.
IJK_EXTERN NSString *const IJKMPMediaPlaybackIsPreparedToPlayDidChangeNotification;
// -----------------------------------------------------------------------------
// MPMoviePlayerController.h
// Movie Player Notifications
// Posted when the scaling mode changes.
IJK_EXTERN NSString* const IJKMPMoviePlayerScalingModeDidChangeNotification;
// Posted when movie playback ends or a user exits playback.
IJK_EXTERN NSString* const IJKMPMoviePlayerPlaybackDidFinishNotification;
IJK_EXTERN NSString* const IJKMPMoviePlayerPlaybackDidFinishReasonUserInfoKey; // NSNumber (IJKMPMovieFinishReason)
// Posted when the playback state changes, either programatically or by the user.
IJK_EXTERN NSString* const IJKMPMoviePlayerPlaybackStateDidChangeNotification;
// Posted when the network load state changes.
IJK_EXTERN NSString* const IJKMPMoviePlayerLoadStateDidChangeNotification;
// Posted when the movie player begins or ends playing video via AirPlay.
IJK_EXTERN NSString* const IJKMPMoviePlayerIsAirPlayVideoActiveDidChangeNotification;
// -----------------------------------------------------------------------------
// Movie Property Notifications
// Calling -prepareToPlay on the movie player will begin determining movie properties asynchronously.
// These notifications are posted when the associated movie property becomes available.
IJK_EXTERN NSString* const IJKMPMovieNaturalSizeAvailableNotification;
// -----------------------------------------------------------------------------
// Extend Notifications
IJK_EXTERN NSString *const IJKMPMoviePlayerVideoDecoderOpenNotification;
IJK_EXTERN NSString *const IJKMPMoviePlayerFirstVideoFrameRenderedNotification;
IJK_EXTERN NSString *const IJKMPMoviePlayerFirstAudioFrameRenderedNotification;
IJK_EXTERN NSString *const IJKMPMoviePlayerDidSeekCompleteNotification;
IJK_EXTERN NSString *const IJKMPMoviePlayerDidSeekCompleteTargetKey;
IJK_EXTERN NSString *const IJKMPMoviePlayerDidSeekCompleteErrorKey;
IJK_EXTERN NSString *const IJKMPMoviePlayerDidAccurateSeekCompleteCurPos;
IJK_EXTERN NSString *const IJKMPMoviePlayerAccurateSeekCompleteNotification;
@end
IJKMediaUrlOpenDelegate
IJKMediaUrlOpenDelegate 在 IJKFFMoviePlayerController 使用，当 ijkplayer 打开HTTP、TCP等相关URL的时候会回调 - (void)willOpenUrl:(IJKMediaUrlOpenData*) urlOpenData 方法。
@protocol IJKMediaUrlOpenDelegate <NSObject>
- (void)willOpenUrl:(IJKMediaUrlOpenData*) urlOpenData;
@end
IJKMediaNativeInvokeDelegate
IJKMediaNativeInvokeDelegate 在 IJKFFMoviePlayerController 使用，当FFmpeg 在处理相关事件（如：AVAPP_EVENT_WILL_HTTP_OPEN、AVAPP_EVENT_DID_HTTP_OPEN、AVAPP_EVENT_WILL_HTTP_SEEK、AVAPP_EVENT_DID_HTTP_SEEK）的时候回调代理的 - (int)invoke:(IJKMediaEvent)event attributes:(NSDictionary *)attributes 方法。
@protocol IJKMediaNativeInvokeDelegate <NSObject>
- (int)invoke:(IJKMediaEvent)event attributes:(NSDictionary *)attributes;
@end
总结
ijkplayer 里面的协议比较简单，协议的数量也不是很多。ijkplayer 提供了几种不同实现的播放器，虽然这几种播放器的实现不同，但都提供了统一的接口。因此，我们并不需要关心实现细节。
