录制好的视频我们可以处理成慢速或者快速的效果。还是十分简单，AVMutableCompositionTrack这个类已经开放了接口scaleTimeRange: toDuration:,我们只需要处理成所想要的效果即可。不多说，还是直接上代码：
// 获取视频
AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:_fileURL options:nil];
// 视频混合
AVMutableComposition* mixComposition = [AVMutableComposition composition];
// 视频轨道
AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
// 音频轨道
AVMutableCompositionTrack *compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
// 视频的方向
CGAffineTransform videoTransform = [videoAsset tracksWithMediaType:AVMediaTypeVideo].lastObject.preferredTransform;
if (videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0) {
NSLog(@"垂直拍摄");
videoTransform = CGAffineTransformMakeRotation(M_PI_2);
}else if (videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0) {
NSLog(@"倒立拍摄"); videoTransform = CGAffineTransformMakeRotation(-M_PI_2);
}else if (videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0) {
NSLog(@"Home键右侧水平拍摄");
videoTransform = CGAffineTransformMakeRotation(0);
}else if (videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0) {
NSLog(@"Home键左侧水平拍摄");
videoTransform = CGAffineTransformMakeRotation(M_PI);
}
// 根据视频的方向同步视频轨道方向
compositionVideoTrack.preferredTransform = videoTransform;
//时间刻度
compositionVideoTrack.naturalTimeScale = 600;
// 插入视频轨道
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMake(videoAsset.duration.value, videoAsset.duration.timescale)) ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] firstObject] atTime:kCMTimeZero error:nil];
// 插入音频轨道
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMake(videoAsset.duration.value, videoAsset.duration.timescale)) ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeAudio] firstObject] atTime:kCMTimeZero error:nil];
// 适配视频速度比率 譬如慢速4 快速0.3
//10s的视频会处理成40s
CGFloat scale = 4;
[compositionVideoTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMake(videoAsset.duration.value,videoAsset.duration.timescale)) toDuration:CMTimeMake(videoAsset.duration.value*scale, videoAsset.duration.timescale)];
[compositionAudioTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMake(videoAsset.duration.value,videoAsset.duration.timescale)) toDuration:CMTimeMake(videoAsset.duration.value*scale, videoAsset.duration.timescale)];
NSLog(@"输出时间结构体");
CMTimeShow(videoAsset.duration);
//合成视频输出路径
NSString *path =[self getVideoSaveFilePathString:@".MOV" addPathArray:NO];
//输出
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition
presetName:AVAssetExportPreset1280x720];
exporter.outputURL = [NSURL fileURLWithPath:path];
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
[exporter exportAsynchronouslyWithCompletionHandler:^{
dispatch_async(dispatch_get_main_queue(), ^{
switch (exporter.status) {
case AVAssetExportSessionStatusCompleted:{
//保存到相册
[self savePhotosAlbum:exporter.outputURL];
}
break;
default:
break;
}
});
}];
注意这里与实时慢速拍摄视频不同。实时慢速拍摄视频也十分简单，查阅GPUImage的头文件发现GPUImageVideoCamera下发现了frameRate这个属性，譬如我们可以设置videoCamera.frameRate =5;这样就可以实现实时慢速拍摄视频了，简单吧。经过实验，发现frameRate的取值范围在0-30之间。
有什么问题，欢迎留言讨论。
