生活中我们经常可能碰到这么一种需求，你有两段视频，你想将两段视频组合成一个视频，你还想为组合的这段新视频添加背景音乐，这就要用到媒体组合技术，AVMutableComposition是这个技术的一个核心的类，他继承于AVComposition类，AVComposition类又继承于AVAsset资源类。
现在有四段视频，比如视频1，视频2，视频3，视频4，实现功能，将视频1，视频2，视频3组合一段视频，视频3要保证视频3的视频数据和音频数据保持一致，提取视频4的音频数据作为新视频的前段的背景音乐。
@property(nonatomic,strong)AVMutableComposition *mutableComposition;
@property(nonatomic,strong)AVAsset *nebual1Asset;
@property(nonatomic,strong)AVAsset *nebual3Asset;
@property(nonatomic,strong)AVAsset *backhole2Asset;
@property(nonatomic,strong)AVAsset *vidAsset;
@property(nonatomic,strong)AVMutableCompositionTrack *mutableVideoTrack;
@property(nonatomic,strong)AVMutableCompositionTrack *mutableAudioTrack;
@property(nonatomic,strong)AVAsset *compositionAsset;
@property(nonatomic,strong)AVPlayerItem *playerItem;
@property(nonatomic,strong)AVPlayer *player;
@property(nonatomic,strong)AVPlayerLayer *playerLayer;
@property(nonatomic,strong)NSString *storePath;
初始化相关数据
-(void)setAssetInfo
{
NSURL *nebula1Url = [[NSBundle mainBundle] URLForResource:@"01_nebula" withExtension:@"mp4"];
NSURL *nebula3Url = [[NSBundle mainBundle] URLForResource:@"03_nebula" withExtension:@"mp4"];
NSURL *backholeUrl = [[NSBundle mainBundle] URLForResource:@"02_blackhole" withExtension:@"mp4"];
NSURL *vidUrl = [[NSBundle mainBundle] URLForResource:@"video" withExtension:@"mp4"];
self.storePath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
self.storePath = [self.storePath stringByAppendingPathComponent:@"cm.mp4"];
self.nebual1Asset = [AVURLAsset URLAssetWithURL:nebula1Url options:nil];
self.nebual3Asset = [AVURLAsset URLAssetWithURL:nebula3Url options:nil];
self.backhole2Asset = [AVURLAsset URLAssetWithURL:backholeUrl options:nil];
self.vidAsset = [AVURLAsset URLAssetWithURL:vidUrl options:nil];
self.mutableComposition = [AVMutableComposition composition];
//添加音频轨道和视频轨道
self.mutableVideoTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
self.mutableAudioTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
}
组合各视频和音频
- (IBAction)btnClicked:(id)sender
{
CMTime startTime = kCMTimeZero;
CMTime duration = self.nebual1Asset.duration;
AVAssetTrack *video1Track = [[self.nebual1Asset tracksWithMediaType:AVMediaTypeVideo] firstObject];
// 向视频轨道中添加媒体片段
[self.mutableVideoTrack insertTimeRange:CMTimeRangeMake(startTime, duration) ofTrack:video1Track atTime:kCMTimeZero error:nil];
AVAssetTrack *video2Track = [[self.nebual3Asset tracksWithMediaType:AVMediaTypeVideo]firstObject];
// 向视频轨道中添加媒体片段
[self.mutableVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, self.nebual3Asset.duration) ofTrack:video2Track atTime:CMTimeAdd(startTime, duration) error:nil];
AVAssetTrack *vidVideoTrack = [[self.vidAsset tracksWithMediaType:AVMediaTypeVideo] firstObject];
// 向视频轨道中添加媒体片段
[self.mutableVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, self.vidAsset.duration) ofTrack:vidVideoTrack atTime:CMTimeAdd(self.nebual3Asset.duration, self.nebual1Asset.duration) error:nil];
AVAssetTrack *audioTrack = [[self.backhole2Asset tracksWithMediaType:AVMediaTypeAudio] firstObject];
// 向音频轨道中添加媒体片段
[self.mutableAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeAdd(self.nebual3Asset.duration, self.nebual1Asset.duration)) ofTrack:audioTrack atTime:kCMTimeZero error:nil];
AVAssetTrack *vidAudioTrack = [[self.vidAsset tracksWithMediaType:AVMediaTypeAudio] firstObject];
// 向音频轨道中添加媒体片段
[self.mutableAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, self.vidAsset.duration) ofTrack:vidAudioTrack atTime:CMTimeAdd(self.nebual1Asset.duration, self.nebual3Asset.duration) error:nil];
//导出
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc]initWithAsset:self.mutableComposition presetName:AVAssetExportPresetMediumQuality];
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
exportSession.outputURL = [NSURL fileURLWithPath:self.storePath];
[exportSession exportAsynchronouslyWithCompletionHandler:^{
//导出完成
if (exportSession.status == AVAssetExportSessionStatusCompleted ) { //横屏播放
[self switchScreen];
//简单播放
[self playerCompostionVideo];
}
}];
}
横屏实现，强制横屏主要用当前的设备的setOrientation方法，当然首先需要判断是否能够响应该方法，如何可以就调用，这里使用了NSInvocation调用对象，其实NSInvocation封装了调用函数所需的所有的信息，比如那个对象发起调用－target，调用哪个方法－selector，调用的参数setArgument设置，如何有返回值也可以通过getReturn方法得到，这里需要注意的是使用setArgument设置参数时参数的索引之从2开始，其实这一点一点都不奇怪，我们要知道IMP函数指针指向的函数前两个参数就是隐藏的target，selector，所有从2开始。
-(void)switchScreen
{
dispatch_async(dispatch_get_main_queue(), ^{
if ([[UIDevice currentDevice] respondsToSelector:@selector(setOrientation:)])
{
SEL selector=NSSelectorFromString(@"setOrientation:");
NSInvocation *invocation =[NSInvocation invocationWithMethodSignature:[UIDevice instanceMethodSignatureForSelector:selector]];
[invocation setSelector:selector];
[invocation setTarget:[UIDevice currentDevice]];
int val =UIInterfaceOrientationLandscapeRight;
[invocation setArgument:&val atIndex:2];
[invocation invoke];
}
});
}
playerCompostionVideo简单的播放
-(void)playerCompostionVideo
{
NSFileManager *fileMange = [NSFileManager defaultManager];
if ([fileMange fileExistsAtPath:self.storePath]) {
NSURL *videoUrl = [NSURL fileURLWithPath:self.storePath];
self.compositionAsset = [AVAsset assetWithURL:videoUrl];
self.playerItem = [[AVPlayerItem alloc] initWithAsset:self.compositionAsset];
//kvo跟踪playerItem的status状态
[self.playerItem addObserver:self forKeyPath:@"status" options:0 context:nil];
self.player = [AVPlayer playerWithPlayerItem:self.playerItem];
self.playerLayer = [AVPlayerLayer playerLayerWithPlayer:self.player];
dispatch_async(dispatch_get_main_queue(), ^{
self.playerLayer.frame = self.view.bounds;
[self.view.layer addSublayer:self.playerLayer];
});
}
}
使用KVO观察AVPlayerItem的status状态，当AVPlayerItemStatusReadyToPlay处于准备播放状态时，开始播放
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
AVPlayerItem *playerItem = (AVPlayerItem*)object;
if (playerItem.status == AVPlayerItemStatusReadyToPlay) {
//播放
[self.player play];
}
}
至此，媒体组合的功能就是实现了，媒体组合技术还是蛮使用的，很多媒体编辑的软件都用得到。
