我已经将这里找到的两个代码块合并为一个完整的代码块（并使用苹果开发者Xcode教程文件验证了该过程）。 然而，当我运行它时，会出现错误。 它说：
有任何想法为什么会抛出AVErrorInvalidVideoComposition错误吗？谢谢！（我是新手，请告知如果需要更多信息。）错误领域= AVFoundationErrorDomain Code=-11841，“操作无法完成。（AVFoundationErrorDomain error -11841.）”
NSURL *videoURL = [info valueForKey:UIImagePickerControllerMediaURL];
/// UIImage into CALayer
UIImage *myImage = [UIImage imageNamed:@"Test.png"];
CALayer *aLayer = [CALayer layer];
aLayer.contents = (id)myImage.CGImage;
AVURLAsset* url = [AVURLAsset URLAssetWithURL:videoURL options:nil];
AVMutableComposition *videoComposition = [[AVMutableComposition alloc] init];
NSError *error;
NSFileManager *fileManager = [NSFileManager defaultManager];
AVMutableCompositionTrack *compositionVideoTrack = [videoComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVAssetTrack *clipVideoTrack = [[url tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [url duration]) ofTrack:clipVideoTrack atTime:kCMTimeZero error:&error];
AVMutableVideoComposition* videoComp = [[AVMutableVideoComposition alloc] init];
videoComp.renderSize = CGSizeMake(640, 480);
videoComp.frameDuration = CMTimeMake(1, 30);
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, videoComp.renderSize.width, videoComp.renderSize.height);
videoLayer.frame = CGRectMake(0, 0, videoComp.renderSize.width, videoComp.renderSize.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:aLayer];
videoComp.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
/// instruction
AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30) );
AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];
instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction];
videoComp.instructions = [NSArray arrayWithObject: instruction];
/// outputs
NSString *filePath = nil;
filePath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
filePath = [filePath stringByAppendingPathComponent:@"temp.mov"];
NSLog(@"exporting to: %@", filePath);
if ([fileManager fileExistsAtPath:filePath])
{
BOOL success = [fileManager removeItemAtPath:filePath error:&error];
if (!success) NSLog(@"FM error: %@", [error localizedDescription]);
}
/// exporting
AVAssetExportSession *exporter;
exporter = [[AVAssetExportSession alloc] initWithAsset:videoComposition presetName:AVAssetExportPresetHighestQuality] ;
exporter.videoComposition = videoComp;
exporter.outputURL=[NSURL fileURLWithPath:filePath];
exporter.outputFileType=AVFileTypeQuickTimeMovie;
[exporter exportAsynchronouslyWithCompletionHandler:^(void){
switch (exporter.status) {
case AVAssetExportSessionStatusFailed:
NSLog(@"exporting failed:%@",exporter.error);
break;
case AVAssetExportSessionStatusCompleted:
NSLog(@"exporting completed");
UISaveVideoAtPathToSavedPhotosAlbum(filePath, self, @selector(video:didFinishSavingWithError:contextInfo:), NULL);
break;
case AVAssetExportSessionStatusCancelled:
NSLog(@"export cancelled");
break;
}
}];