iOS: AVPlayerItem到AVAsset

Question

我得到了2个AVAssets，我使用VideoComposition和AudioMix表示AVPlayerItem进行了更改。在此之后，我使用了来自AVPlayerItem的资产，但是没有应用VideoComposition和AudioMix。我希望VideoComposition和AudioMix应用结果资产。这是密码。

+ (AVAsset *)InitAsset:(AVAsset *)asset AtTime:(double)start ToTime:(double)end {
CGFloat colorComponents[4] = {1.0,1.0,1.0,0.0};

//Create AVMutableComposition Object.This object will hold our multiple AVMutableCompositionTrack.
AVMutableComposition* mixComposition = [[AVMutableComposition alloc] init];

//Here we are creating the first AVMutableCompositionTrack.See how we are adding a new track to our AVMutableComposition.
AVMutableCompositionTrack *masterTrack =
[mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
                            preferredTrackID:kCMPersistentTrackID_Invalid];
//Now we set the length of the firstTrack equal to the length of the firstAsset and add the firstAsset to out newly created track at kCMTimeZero so video plays from the start of the track.
[masterTrack insertTimeRange:CMTimeRangeMake(CMTimeMakeWithSeconds(start, 1), CMTimeMakeWithSeconds(end, 1))
                     ofTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
                      atTime:kCMTimeZero error:nil];

// Each video layer instruction
AVMutableVideoCompositionLayerInstruction *masterLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:masterTrack];
[masterLayerInstruction setOpacity:1.0f atTime:kCMTimeZero];
[masterLayerInstruction setOpacityRampFromStartOpacity:1.0f
                                          toEndOpacity:0.0
                                             timeRange:CMTimeRangeMake(CMTimeMakeWithSeconds(end, 1), CMTimeMakeWithSeconds(end + ANIMATION_FADE_TIME, 1))];

//See how we are creating AVMutableVideoCompositionInstruction object.This object will contain the array of our AVMutableVideoCompositionLayerInstruction objects.You set the duration of the layer.You should add the lenght equal to the lingth of the longer asset in terms of duration.
AVMutableVideoCompositionInstruction * MainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
[MainInstruction setTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(end + ANIMATION_FADE_TIME, 1))];
[MainInstruction setLayerInstructions:[NSArray arrayWithObjects:masterLayerInstruction,nil]];
[MainInstruction setBackgroundColor:CGColorCreate(CGColorSpaceCreateDeviceRGB(), colorComponents)];

//Now we create AVMutableVideoComposition object.We can add mutiple AVMutableVideoCompositionInstruction to this object.We have only one AVMutableVideoCompositionInstruction object in our example.You can use multiple AVMutableVideoCompositionInstruction objects to add multiple layers of effects such as fade and transition but make sure that time ranges of the AVMutableVideoCompositionInstruction objects dont overlap.
AVMutableVideoComposition *MainCompositionInst = [AVMutableVideoComposition videoComposition];
MainCompositionInst.instructions = [NSArray arrayWithObject:MainInstruction];
MainCompositionInst.frameDuration = CMTimeMake(1, 30);
MainCompositionInst.renderSize = CGSizeMake(1280, 720);
//    [MainCompositionInst setFra]

AVMutableCompositionTrack *masterAudio = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[masterAudio insertTimeRange:CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(end + ANIMATION_FADE_TIME, 1))
                     ofTrack:[[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:nil];

// Each Audio
AVMutableAudioMixInputParameters *masterAudioMix = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:masterAudio];
[masterAudioMix setVolume:1.0f atTime:kCMTimeZero];
[masterAudioMix setVolumeRampFromStartVolume:1.0f
                                 toEndVolume:0.0f
                                   timeRange:CMTimeRangeMake(CMTimeMakeWithSeconds(end, 1), CMTimeMakeWithSeconds(end + ANIMATION_FADE_TIME, 1))];
//    [SecondTrackMix setVolume:1.0f atTime:CMTimeMake(2.01, 1)];

AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix];
audioMix.inputParameters = [NSArray arrayWithObjects:masterAudioMix,nil];

//Finally just add the newly created AVMutableComposition with multiple tracks to an AVPlayerItem and play it using AVPlayer.
AVPlayerItem *item = [AVPlayerItem playerItemWithAsset:mixComposition];
item.videoComposition = MainCompositionInst;
item.audioMix = audioMix;

return [item asset];
}

有人知道吗？

诚挚的问候。

Answer 1

用AVAssetExportSeesion..。

“AVAssetExportSession对象对AVAsset源对象的内容进行代码转换，以创建由指定导出预置所描述的表单的输出。”

使用AVAssetExportSeesion的属性audioMix和videoComposition。

audioMix指示是否启用了非默认音频混合以进行导出，并提供音频混合的参数。

@property(非原子，复制) AVAudioMix *audioMix

videoComposition指示是否为导出启用了视频组合，并提供了视频合成的说明。

@property(非原子，复制) AVVideoComposition *视频组合