我在视频中添加水印时AVAssetSessionFailed

Question

我正在创建一个处理视频的应用程序。现在，我想在此视频中添加一个水印，该水印存在于使用AVMutableComposition的应用程序的本地目录中。但是AVAssetExportSession在此过程中失败了。

请在此代码中告诉我我的错误。

   -(void)displayWatermarkInVideo
   {
    NSString *path = [[NSBundle mainBundle]pathForResource:@"Video_20160102191557356_by_videoshow" ofType:@"mp4"];
    NSURL *URL = [NSURL fileURLWithPath:path];
    AVURLAsset *videoAsset = [[AVURLAsset alloc]initWithURL:URL options:nil];
if (!videoAsset) {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Please Load a Video Asset First"
                                                   delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
    return;
}

// 2 - Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.
AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];

// 3 - Video track
AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
                                                                    preferredTrackID:kCMPersistentTrackID_Invalid];
[videoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                    ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
                     atTime:kCMTimeZero error:nil];

// 3.1 - Create AVMutableVideoCompositionInstruction
AVMutableVideoCompositionInstruction *mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, videoAsset.duration);

// 3.2 - Create an AVMutableVideoCompositionLayerInstruction for the video track and fix the orientation.
AVMutableVideoCompositionLayerInstruction *videolayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
AVAssetTrack *videoAssetTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
UIImageOrientation videoAssetOrientation_  = UIImageOrientationUp;
BOOL isVideoAssetPortrait_  = NO;
CGAffineTransform videoTransform = videoAssetTrack.preferredTransform;
if (videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0) {
    videoAssetOrientation_ = UIImageOrientationRight;
    isVideoAssetPortrait_ = YES;
}
if (videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0) {
    videoAssetOrientation_ =  UIImageOrientationLeft;
    isVideoAssetPortrait_ = YES;
}
if (videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0) {
    videoAssetOrientation_ =  UIImageOrientationUp;
}
if (videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0) {
    videoAssetOrientation_ = UIImageOrientationDown;
}
[videolayerInstruction setTransform:videoAssetTrack.preferredTransform atTime:kCMTimeZero];
[videolayerInstruction setOpacity:0.0 atTime:videoAsset.duration];

// 3.3 - Add instructions
mainInstruction.layerInstructions = [NSArray arrayWithObjects:videolayerInstruction,nil];

AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition];

CGSize naturalSize;
if(isVideoAssetPortrait_){
    naturalSize = CGSizeMake(videoAssetTrack.naturalSize.height, videoAssetTrack.naturalSize.width);
} else {
    naturalSize = videoAssetTrack.naturalSize;
}

float renderWidth, renderHeight;
renderWidth = naturalSize.width;
renderHeight = naturalSize.height;
mainCompositionInst.renderSize = CGSizeMake(renderWidth, renderHeight);
mainCompositionInst.instructions = [NSArray arrayWithObject:mainInstruction];
mainCompositionInst.frameDuration = CMTimeMake(1, 30);

NSLog(@"naturalSize %f %f", naturalSize.width, naturalSize.height);

// no-op - override this method in the subclass
// 1 - Set up the text layer
CGSize sizeOfVideo=[videoAsset naturalSize];
CATextLayer *subtitle1Text = [[CATextLayer alloc] init];
[subtitle1Text setFont:@"Helvetica-Bold"];
[subtitle1Text setFontSize:20];
[subtitle1Text setFrame:CGRectMake(0, 0, sizeOfVideo.width, 100)];
[subtitle1Text setString:@"Your Text.."];
[subtitle1Text setAlignmentMode:kCAAlignmentCenter];
[subtitle1Text setForegroundColor:[[UIColor whiteColor] CGColor]];

// 2 - The usual overlay
CALayer *overlayLayer = [CALayer layer];
[overlayLayer addSublayer:subtitle1Text];
overlayLayer.frame = CGRectMake(0, 0, sizeOfVideo.width, sizeOfVideo.height);
[overlayLayer setMasksToBounds:YES];

CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, sizeOfVideo.width, sizeOfVideo.height);
videoLayer.frame = CGRectMake(0, 0, sizeOfVideo.width, sizeOfVideo.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:overlayLayer];
AVMutableVideoComposition *videoComposition=[AVMutableVideoComposition videoComposition] ;
videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool
                             videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

// 4 - Get path
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *myPathDocs =  [documentsDirectory stringByAppendingPathComponent:
                         [NSString stringWithFormat:@"WatermarkVideo-%d.mp4",arc4random() % 1000]];
NSURL *url = [NSURL fileURLWithPath:myPathDocs];

// 5 - Create exporter
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition
                                                                  presetName:AVAssetExportPresetHighestQuality];
exporter.outputURL=url;
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = mainCompositionInst;

[exporter exportAsynchronouslyWithCompletionHandler:^{
   dispatch_async(dispatch_get_main_queue(), ^{

        if (exporter.status == AVAssetExportSessionStatusCompleted) {
            NSLog(@"Export complete");
            NSURL *outputURL = exporter.outputURL;
            ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
            if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:outputURL]) {
                [library writeVideoAtPathToSavedPhotosAlbum:outputURL completionBlock:^(NSURL *assetURL, NSError *error){
                    dispatch_async(dispatch_get_main_queue(), ^{
                        if (error) {
                            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Video Saving Failed" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
                            [alert show];
                       } else {
                            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Video Saved" message:@"Saved To Photo Album" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
                           [alert show];
                       }
                    });
                }];
            }
       }

   });
}];
}