iOS - AVAssestExportSession播放AVPlayer后最多只能导出8首曲目

Question

我正在尝试循环录制视频的一些片段，并将它们合并到一个视频中。我已经成功地合并并导出了一个最多16首曲目的乐曲。但是当我尝试在合并前使用AVPlayer播放乐曲时，我最多只能导出8首曲目。

首先，我创建了AVComposition和AVVideoComposition

    +(void)previewUserClipDanceWithAudio:(NSURL*)videoURL audioURL:(NSURL*)audioFile loop:(NSArray*)loopTime slowMotion:(NSArray*)slowFactor showInViewController:(UIViewController*)viewController completion:(void(^)(BOOL success, AVVideoComposition* videoComposition, AVComposition* composition))completion{

AVMutableComposition* mixComposition = [[AVMutableComposition alloc] init];
NSMutableArray *arrayInstruction = [[NSMutableArray alloc] init];
AVMutableVideoCompositionInstruction *videoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

AVURLAsset  *audioAsset = [[AVURLAsset alloc]initWithURL:audioFile options:nil];
//NSLog(@"audio File %@",audioFile);

CMTime duration = kCMTimeZero;

AVAsset *currentAsset = [AVAsset assetWithURL:videoURL];
BOOL  isCurrentAssetPortrait  = YES;

for(NSInteger i=0;i< [loopTime count]; i++) {

    //handle looptime array
    NSInteger loopDur = [[loopTime objectAtIndex:i] intValue];
    NSInteger value = labs(loopDur);
    //NSLog(@"loopInfo %d value %d",loopInfo,value);
    //handle slowmotion array
    double slowInfo = [[slowFactor objectAtIndex:i] doubleValue];
    double videoScaleFactor = fabs(slowInfo);

    AVMutableCompositionTrack *currentTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    AVMutableCompositionTrack *audioTrack;
    audioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio
                                             preferredTrackID:kCMPersistentTrackID_Invalid];
    if (i==0) {
        [currentTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, currentAsset.duration) ofTrack:[[currentAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:duration error:nil];

        [audioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, currentAsset.duration) ofTrack:[[currentAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:duration error:nil];

    } else {

        [currentTrack insertTimeRange:CMTimeRangeMake(CMTimeSubtract(currentAsset.duration, CMTimeMake(value, 10)), CMTimeMake(value, 10)) ofTrack:[[currentAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:duration error:nil];

        if (videoScaleFactor==1) {

            [audioTrack insertTimeRange:CMTimeRangeMake(CMTimeSubtract(currentAsset.duration, CMTimeMake(value, 10)), CMTimeMake(value, 10)) ofTrack:[[currentAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:duration error:nil];
        }
        //slow motion here
        if (videoScaleFactor!=1) {

            [currentTrack scaleTimeRange:CMTimeRangeMake(CMTimeSubtract(currentAsset.duration, CMTimeMake(value, 10)), CMTimeMake(value, 10))
                              toDuration:CMTimeMake(value*videoScaleFactor, 10)];
            NSLog(@"slowmo %f",value*videoScaleFactor);
        }
    }

    AVMutableVideoCompositionLayerInstruction *currentAssetLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:currentTrack];
    AVAssetTrack *currentAssetTrack = [[currentAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

    BOOL  isCurrentAssetPortrait  = YES;
    //CGFloat assetScaleToFitRatio;
    //assetScaleToFitRatio = [self getScaleToFitRatioCurrentTrack:currentTrack];

    if(isCurrentAssetPortrait){
        //NSLog(@"portrait");
        if (slowInfo<0) {
            CGRect screenRect = [[UIScreen mainScreen] bounds];
            CGFloat ratio = screenRect.size.height / screenRect.size.width;

            // we have to adjust the ratio for 16:9 screens
            if (ratio == 1.775) ratio = 1.77777777777778;

            CGFloat complimentSize = (currentAssetTrack.naturalSize.height*ratio);
            CGFloat tx = (currentAssetTrack.naturalSize.width-complimentSize)/2;

            // invert translation because of portrait
            tx *= -1;
            // t1: rotate and position video since it may have been cropped to screen ratio
            CGAffineTransform t1 = CGAffineTransformTranslate(currentAssetTrack.preferredTransform, tx, 0);
            // t2/t3: mirror video vertically

            CGAffineTransform t2 = CGAffineTransformTranslate(t1, currentAssetTrack.naturalSize.width, 0);
            CGAffineTransform t3 = CGAffineTransformScale(t2, -1, 1);

            [currentAssetLayerInstruction setTransform:t3 atTime:duration];

        } else if (loopDur<0) {
            CGRect screenRect = [[UIScreen mainScreen] bounds];
            CGFloat ratio = screenRect.size.height / screenRect.size.width;

            // we have to adjust the ratio for 16:9 screens
            if (ratio == 1.775) ratio = 1.77777777777778;

            CGFloat complimentSize = (currentAssetTrack.naturalSize.height*ratio);
            CGFloat tx = (currentAssetTrack.naturalSize.width-complimentSize)/2;

            // invert translation because of portrait
            tx *= -1;
            // t1: rotate and position video since it may have been cropped to screen ratio
            CGAffineTransform t1 = CGAffineTransformTranslate(currentAssetTrack.preferredTransform, tx, 0);
            // t2/t3: mirror video horizontally
            CGAffineTransform t2 = CGAffineTransformTranslate(t1, 0, currentAssetTrack.naturalSize.height);
            CGAffineTransform t3 = CGAffineTransformScale(t2, 1, -1);

            [currentAssetLayerInstruction setTransform:t3 atTime:duration];

        } else {

            [currentAssetLayerInstruction setTransform:currentAssetTrack.preferredTransform atTime:duration];

        }
    }else{
        //            CGFloat translateAxisX = (currentTrack.naturalSize.width > MAX_WIDTH )?(0.0):0.0;// if use <, 640 video will be moved left by 10px. (float)(MAX_WIDTH - currentTrack.naturalSize.width)/(float)4.0
        //            CGAffineTransform FirstAssetScaleFactor = CGAffineTransformMakeScale(assetScaleToFitRatio,assetScaleToFitRatio);
        //            [currentAssetLayerInstruction setTransform:
        //             CGAffineTransformConcat(CGAffineTransformConcat(currentAssetTrack.preferredTransform, FirstAssetScaleFactor),CGAffineTransformMakeTranslation(translateAxisX, 0)) atTime:duration];
    }
    if (i==0) {
        duration=CMTimeAdd(duration, currentAsset.duration);
    } else  {
        if (videoScaleFactor!=1) {
            duration=CMTimeAdd(duration, CMTimeMake(value*videoScaleFactor, 10));
        } else {
            duration=CMTimeAdd(duration, CMTimeMake(value, 10));
        }
    }

    [currentAssetLayerInstruction setOpacity:0.0 atTime:duration];
    [arrayInstruction addObject:currentAssetLayerInstruction];
}

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

videoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, duration);
videoCompositionInstruction.layerInstructions = arrayInstruction;

CGSize naturalSize;
if(isCurrentAssetPortrait){
    naturalSize = CGSizeMake(MAX_HEIGHT,MAX_WIDTH);//currentAssetTrack.naturalSize.height,currentAssetTrack.naturalSize.width);
} else {
    naturalSize = CGSizeMake(MAX_WIDTH,MAX_HEIGHT);//currentAssetTrack.naturalSize;
}

AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.instructions = [NSArray arrayWithObject:videoCompositionInstruction];
videoComposition.frameDuration = CMTimeMake(1, 30);
videoComposition.renderSize = CGSizeMake(naturalSize.width,naturalSize.height);
NSLog(@"prepared");

AVVideoComposition *composition = [videoComposition copy];
AVComposition *mixedComposition = [mixComposition copy];
completion(YES, composition, mixedComposition);
}

然后，我设置了AVPlayer

    -(void)playVideoWithComposition:(AVVideoComposition*)videoComposition inMutableComposition:(AVComposition*)composition{

MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
hud.label.text = myLanguage(@"kMergeClip");

savedComposition = [composition copy];
savedVideoComposition = [videoComposition copy];
playerItem = [AVPlayerItem playerItemWithAsset:composition];
playerItem.videoComposition = videoComposition;

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(repeatVideo:) name:AVPlayerItemDidPlayToEndTimeNotification object:playerItem];

if (!player) {
    player = [AVPlayer playerWithPlayerItem:playerItem];
    layer = [AVPlayerLayer playerLayerWithPlayer:player];
    layer.frame = [UIScreen mainScreen].bounds;
    [self.ibPlayerView.layer insertSublayer:layer atIndex:0];
    NSLog(@"create new player");
}

if (player.currentItem != playerItem ) {
    [player replaceCurrentItemWithPlayerItem:playerItem];
}
player.actionAtItemEnd = AVPlayerActionAtItemEndNone;
//[player seekToTime:kCMTimeZero];

[playerItem addObserver:self
             forKeyPath:@"status"
                options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
                context:@"AVPlayerStatus"];
}

当用户预览所有他们想要的视频并点击保存。我使用此方法导出

    +(void)mergeUserCLip:(AVVideoComposition*)videoComposition withAsset:(AVComposition*)mixComposition showInViewController:(UIViewController*)viewController completion:(void(^)(BOOL success, NSURL *fileURL))completion{

MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:viewController.view animated:YES];
hud.mode = MBProgressHUDModeDeterminateHorizontalBar;
hud.label.text = myLanguage(@"kMergeClip");

//Name merge clip using beat name
//NSString* beatName = [[[NSString stringWithFormat:@"%@",audioFile] lastPathComponent] stringByDeletingPathExtension];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *tmpDir = [[documentsDirectory stringByDeletingLastPathComponent] stringByAppendingPathComponent:@"tmp"];
NSString *myPathDocs =  [tmpDir stringByAppendingPathComponent:[NSString stringWithFormat:@"merge-beat.mp4"]];
//Not remove here, will remove when call previewPlayVC
[[NSFileManager defaultManager] removeItemAtPath:myPathDocs error:nil];

// 1 - set up the overlay
CALayer *overlayLayer = [CALayer layer];
UIImage *overlayImage = [UIImage imageNamed:@"watermark.png"];

[overlayLayer setContents:(id)[overlayImage CGImage]];
overlayLayer.frame = CGRectMake(720-221, 1280-109, 181, 69);
[overlayLayer setMasksToBounds:YES];

//    aLayer  = [CALayer layer];
//    [aLayer addSublayer:labelLogo.layer];
//    aLayer.frame = CGRectMake(MAX_WIDTH- labelLogo.width - 10.0, MAX_HEIGHT-50.0, 20.0, 20.0);
//    aLayer.opacity = 1;

// 2 - set up the parent layer
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, MAX_HEIGHT,MAX_WIDTH);
videoLayer.frame = CGRectMake(0, 0, MAX_HEIGHT,MAX_WIDTH);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:overlayLayer];

// 3 - apply magic
AVMutableVideoComposition *mutableVideoComposition = [videoComposition copy];
mutableVideoComposition.animationTool = [AVVideoCompositionCoreAnimationTool
                                  videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

NSURL *url = [NSURL fileURLWithPath:myPathDocs];
myLog(@"Path: %@", myPathDocs);
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPreset1280x720];
exporter.outputURL = url;
exporter.outputFileType = AVFileTypeMPEG4;
exporter.videoComposition = mutableVideoComposition;
exporter.shouldOptimizeForNetworkUse = NO;

[exporter exportAsynchronouslyWithCompletionHandler:^ {
    //NSLog(@"exporting");
    switch (exporter.status) {
        case AVAssetExportSessionStatusCompleted: {
            NSURL *url = [NSURL fileURLWithPath:myPathDocs];
            hud.progress = 1.0f;
            dispatch_async(dispatch_get_main_queue(), ^{
                [MBProgressHUD hideHUDForView:viewController.view animated:YES];
            });
            [self checkTmpSize];
            if (completion) {
                completion(YES, url);
            }
        }
            break;
        case AVAssetExportSessionStatusExporting:
            myLog(@"Exporting!");
            break;
        case AVAssetExportSessionStatusWaiting:
            myLog(@"Waiting");
            break;
        default:
            break;
    }
}];
}

如果选择选项的循环次数少于8次，则上面的代码可以正常工作。如果选择选项的次数超过8次，如果删除此行，导出会话将冻结并显示export.progress = 0.0000000

    playerItem.videoComposition = videoComposition;

然后我无法预览混合视频，但可以正常导出(最多16首曲目)。

或者，如果我删除导出代码中的行：

    exporter.videoComposition = mutableVideoComposition;

然后可以预览混合的视频，并正常导出，而不使用视频合成。

所以我猜AVVideoComposition和/或我实现它的方式有问题。

如果有任何建议，我将不胜感激。非常感谢。

我高度怀疑这是因为使用AVPlayer预览视频以某种方式阻碍了AVAssetExportSession，如以下帖子所述：

iOS 5: Error merging 3 videos with AVAssetExportSession

AVPlayerItem fails with AVStatusFailed and error code “Cannot Decode”

Answer 1

我在UICollectionView中尝试连接N个视频，同时在AVPlayer实例中播放最多3个视频时遇到了这个问题。在您链接的Stack Overflow question中已经讨论过，iOS只能处理这么多的AVPlayer实例。每个实例都会耗尽一个“渲染管道”。我发现AVMutableCompositionTrack的每个实例也会占用这些渲染管道中的一个。

因此，如果您使用过多的AVPlayer实例或尝试创建一个包含过多AVMutableCompositionTrack曲目的AVMutableComposition，您可能会耗尽用于解码H264的资源，并且您将收到"Cannot Decode“错误。我只使用了两个AVMutableCompositionTrack实例就解决了这个问题。这样，我可以在应用过渡的同时“重叠”视频片段(这需要同时“播放”两个视频曲目)。

简而言之:最小化您对AVMutableCompositionTrack和AVPlayer的使用。你可以查看苹果公司的AVCustomEdit示例代码，以获得这方面的示例。具体地说，检查APLSimpleEditor类内部的buildTransitionComposition方法。

Answer 2

尝试此操作，在导出前清除播放器项目

[self.player replaceCurrentItemWithPlayerItem:nil];