Concat视频序列

Question

尝试使用此消息连接视频序列时，我收到了AVAssetExportSessionStatusFailed：

Export Failed with error messsage: Error
Domain=AVFoundationErrorDomain Code=-11841 "Operation Stopped"
UserInfo=0x170675cc0 {NSLocalizedDescription=Operation Stopped,
NSLocalizedFailureReason=The video could not be composed.}, Operation
Stopped

这是我的代码：

self.finalComposition = [AVMutableComposition composition];
self.finalCompositionTrack = [_finalComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
self.finalCompositionAudioTrack = [_finalComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

CMTime currentTime = kCMTimeZero;

AVURLAsset *asset = nil;
NSMutableArray *audioTracks = [[NSMutableArray alloc] init];
NSMutableArray *videos = [[NSMutableArray alloc] init];

for (int videoCounter = 0; videoCounter < _videoArray.count ; videoCounter++)
{
    id object = [_videoArray objectAtIndex:videoCounter];

    if ([object isKindOfClass:[MVideoRecord class]])
    {
        MVideoRecord *video = object;
        NSURL *url = [NSURL fileURLWithPath:video.pathToVideo];

        NSFileManager *fileManager = [NSFileManager defaultManager];
        if (![fileManager fileExistsAtPath:video.pathToVideo])
        {
            [self showError:@"Invalid video"];
        }

        NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];

        asset = [AVURLAsset URLAssetWithURL:url options:options];

        NSError *error = nil;
        if (!self.videoCompostion)
        {
            self.videoCompostion = [AVMutableVideoComposition videoComposition];
            self.videoCompostion.frameDuration = CMTimeMake(1, 30);
            self.videoCompostion.renderSize = CGSizeMake(640, 360);
            self.videoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
            videoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, totalTime);
            self.videoCompositionLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:self.finalCompositionTrack];
        }

        for  (AVAssetTrack *track in asset.tracks)
        {
            CGSize size = track.naturalSize;

            if(track.naturalTimeScale == 600)
            {
                CGAffineTransform transform = [track preferredTransform];
                int orientation = [self orientationForTrack: asset];

                if (orientation < 2)
                {
                    float x = 640/size.width;
                    float y = 360/size.height;


                    CGAffineTransform videoScale = CGAffineTransformMakeScale(x, y);

                    [_videoCompositionLayerInstruction setTransform:CGAffineTransformConcat(transform, videoScale) atTime:currentTime];                    }
                else
                {
                    float s = 480/size.height;
                    CGAffineTransform new = CGAffineTransformConcat(transform, CGAffineTransformMakeScale(s,s));
                    [_videoCompositionLayerInstruction setTransform:new atTime:currentTime];
                }

                if (![_finalCompositionTrack insertTimeRange:CMTimeRangeMake(CMTimeMakeWithSeconds(video.videoStart.doubleValue, 600), CMTimeMakeWithSeconds(video.videoEnd.doubleValue, 600)) ofTrack:track atTime:currentTime error:&error])
                {
                    [self showError:error.localizedFailureReason];
                }
            }
            else if (track.naturalTimeScale == 44100)
            {
                CMTime start = kCMTimeZero;
                CMTime duration = CMTimeMakeWithSeconds(video.videoEnd.doubleValue, 600);

                NSError *error;
                [finalCompositionAudioTrack insertTimeRange:CMTimeRangeMake(start, duration)
                                    ofTrack:[[track.asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:currentTime error:&error];

                NSLog(@"%@", error);
            }
        }
        currentTime = CMTimeAdd(currentTime, CMTimeMake(video.videoEnd.doubleValue*600, 600));
    }
}

//apply the translation to video composition
_videoCompositionInstruction.layerInstructions = [NSArray arrayWithObject: _videoCompositionLayerInstruction];
_videoCompostion.instructions = [NSArray arrayWithObject:_videoCompositionInstruction];

//get filepath of last object...
MVideoRecord *lastRecord = [_videoArray objectAtIndex:_videoArray.count - 2];

NSString *finalExportURLString = [lastRecord.pathToVideo stringByReplacingOccurrencesOfString:@".MOV" withString:@"_finalExport.mp4"];

//testing fix for video missing audio after final export
//string = [exportURL.absoluteString stringByReplacingOccurrencesOfString:@".MOV" withString:@"_finalExport.MOV"];


// File Management
NSFileManager *fileManager = [NSFileManager defaultManager];

self.finalExportURL = [NSURL fileURLWithPath:finalExportURLString];
self.finalExportSession = [[AVAssetExportSession alloc] initWithAsset:_finalComposition presetName:TEST_EXPORT_SESSION_QUALITY];
if ([fileManager fileExistsAtPath:finalExportURL.path])
{
    NSError *fileError = nil;
    if (![fileManager removeItemAtPath:finalExportURLString error:&fileError])
    {
        DCLog(@"Error removing old path: %@", fileError.localizedDescription);
    }
}

_finalExportSession.outputURL = self.finalExportURL;
_finalExportSession.outputFileType =  @"public.mpeg-4";
_finalExportSession.videoComposition = self.videoCompostion;

[self.finalExportSession exportAsynchronouslyWithCompletionHandler:^{
    switch (_finalExportSession.status)
    {    case AVAssetExportSessionStatusFailed:
        {
            DCLog(@"Export Failed with error messsage: %@, %@", _finalExportSession.error, _finalExportSession.error.localizedDescription);
            break;
        }
        case AVAssetExportSessionStatusCompleted:
        {
            DCLog(@"Export Success");                
            break;
        }
    };
}];

我做错了什么？

最奇怪的是，如果我改变：

[finalCompositionAudioTrack insertTimeRange:CMTimeRangeMake(start, duration)
                                        ofTrack:[[track.asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:currentTime error:&error];

为：

[finalCompositionAudioTrack insertTimeRange:CMTimeRangeMake(start, duration)
                                        ofTrack:[[track.asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:&error];

它有效，但当然，音频播放错误。第一个视频的音频播放第二个视频。