AVAssetExportSession使用说明制作黑屏

Question

我正在尝试将2个音频文件和1个视频文件组合成1个.mov文件。我用下一段代码实现了这一点：

-(void)combineData{
AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];

AVAsset *audioAsset = [AVAsset assetWithURL:_songURL];
AVAsset* audioAsset2 = [AVAsset assetWithURL:[NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:[@"speechRecord" stringByAppendingPathExtension:@"caf"]]]];
AVURLAsset *videoAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:[@"movie" stringByAppendingPathExtension:@"mov"]]] options:nil];

AVMutableCompositionTrack *firstTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[firstTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) ofTrack:[[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:nil];

AVMutableCompositionTrack *secondTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[secondTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) ofTrack:[[audioAsset2 tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:nil];

AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[videoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:nil];

AVMutableVideoCompositionLayerInstruction *layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
/*CGAffineTransform rotationTransform = CGAffineTransformMakeRotation(DEGREES_TO_RADIANS(90));
CGAffineTransform rotateTranslate = CGAffineTransformTranslate(rotationTransform,320,0);*/
[layerInstruction setTransform:videoTrack.preferredTransform atTime:kCMTimeZero];

AVMutableVideoCompositionInstruction * mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, videoAsset.duration);
[mainInstruction setLayerInstructions:[NSArray arrayWithObject:layerInstruction]];

mixComposition.naturalSize = videoTrack.naturalSize;

AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition];
mainCompositionInst.renderScale = 1.0;
mainCompositionInst.renderSize = videoTrack.naturalSize;
mainCompositionInst.frameDuration = CMTimeMake(1, 30);
mainCompositionInst.instructions = [NSArray arrayWithObject:mainInstruction];
//mainCompositionInst.

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *myPathDocs =  [documentsDirectory stringByAppendingPathComponent:@"mergeVideo.mov"];

if ([[NSFileManager defaultManager] fileExistsAtPath:myPathDocs]) {
    [[NSFileManager defaultManager] removeItemAtPath:myPathDocs error:nil];
    NSLog(@"Removing old mergeVideo");
}

NSURL *url = [NSURL fileURLWithPath:myPathDocs];

AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];
exporter.outputURL=url;
exporter.outputFileType = AVFileTypeQuickTimeMovie; 
exporter.videoComposition = mainCompositionInst;
exporter.shouldOptimizeForNetworkUse = YES; 

[exporter exportAsynchronouslyWithCompletionHandler:^ 
 {
     dispatch_async(dispatch_get_main_queue(), ^{
         [self exportDidFinish:exporter];
     });
 }];

我的第一个任务是处理90转我的新视频。当我将mainCompositionInst包含到我的代码中时，我的新视频有所有的声音，但它有一个黑屏，并且仍然没有旋转。如果我不使用任何指令，它工作得很好。也许我的代码中有错误，也可能没有。你对我有什么建议？

Answer 1

我会尝试在preferredTransform上应用旋转，因为preferredTransform可能会转换您的视频，使其正确显示在屏幕上。

我会尝试以下几点：

CGAffineTransform transform = videoTrack.preferredTransform;
transform = CGAffineTransformRotate(transform, DEGREES_TO_RADIANS(90));
//transform = CGAffineTransformTranslate(transform, 320, 0);
[layerInstruction setTransform:transform atTime:kCMTimeZero];

Answer 2

可在此处找到适当的工作示例：https://github.com/robovm/apple-ios-samples/blob/master/AVSimpleEditoriOS/AVSimpleEditor/AVSERotateCommand.m#L98

正如Apple示例源代码中的注释所述，您需要平移构图以补偿旋转引起的移动(因为旋转会导致它移出帧)。

要应用的正确翻译为：

t1 = CGAffineTransformMakeTranslation(assetVideoTrack.naturalSize.height, 0.0);
// Rotate transformation
t2 = CGAffineTransformRotate(t1, degreesToRadians(90.0));