在播放期间更改 AVPlayerItem 的 videoComposition 属性 (AVMutableVideoComposition)

Posted 2023-03-11

【中文标题】在播放期间更改 AVPlayerItem 的 videoComposition 属性 (AVMutableVideoComposition)

【英文标题】：Changing AVPlayerItem's videoComposition property (AVMutableVideoComposition) during playback

【发布时间】：2012-05-19 08:46:35

【问题描述】：

我正在尝试在播放期间更改视频合成的布局（即其组件帧的变换）。似乎有时这是可行的，并且视频合成无缝地更改为新的转换集，但其他时候它只是冻结并保持当前的转换。 AVPlayer 实例的状态码没有变化，播放器和播放器项目都没有错误。

以前有人经历过吗？对于为什么会发生这种情况或如何解决它的任何建议，我们将不胜感激。

一些代码如下所示。重要的一点是“playerItem.videoComposition = videoComposition”，这里是在点击视频时触发的（用于测试目的）。

解决此问题的另一种方法是将视频显示在不同的图层上，但视频必须保持同步，因此合成似乎是实现此目的的唯一方法。

@implementation VideoView

    CGSize _videoSize;
    CMTimeRange _videoFullRange;

    AVMutableCompositionTrack * _compositionTrackVideoA;
    AVMutableCompositionTrack * _compositionTrackVideoB;


+ (Class)layerClass

    return [AVPlayerLayer class];


- (id)initWithFrame:(CGRect)frame

    self = [super initWithFrame:frame];
    if ( self )
    
        NSString * videoAPath = [[NSBundle mainBundle] pathForResource:@"cam09v2" ofType:@"mp4"];
        NSString * videoBPath = [[NSBundle mainBundle] pathForResource:@"cam10v2_b" ofType:@"mp4"];
        AVURLAsset * videoAAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:videoAPath] options:nil];
        AVURLAsset * videoBAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:videoBPath] options:nil];

        AVAssetTrack * videoATrack = [[videoAAsset tracksWithMediaType:AVMediaTypeVideo] lastObject];
        AVAssetTrack * videoBTrack = [[videoBAsset tracksWithMediaType:AVMediaTypeVideo] lastObject];
        AVAssetTrack * audioTrack = [[videoAAsset tracksWithMediaType:AVMediaTypeAudio] lastObject];

        _videoSize = [videoATrack naturalSize];
        CMTime videoDuration = videoAAsset.duration;
        _videoFullRange = CMTimeRangeMake(kCMTimeZero, videoDuration);

        AVMutableComposition *composition = [AVMutableComposition composition];
        AVMutableCompositionTrack * compositionTrackVideoA = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
        AVMutableCompositionTrack * compositionTrackVideoB = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
        AVMutableCompositionTrack * compositionTrackAudio = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

        compositionTrackVideoA.preferredTransform = videoATrack.preferredTransform;

        NSError * error = nil;
        if ( ! [compositionTrackVideoA insertTimeRange:_videoFullRange ofTrack:videoATrack atTime:kCMTimeZero error:&error] )
            NSLog(@"%@", error);

        if ( ! [compositionTrackVideoB insertTimeRange:_videoFullRange ofTrack:videoBTrack atTime:kCMTimeZero error:&error] )
            NSLog(@"%@", error);

        if ( ! [compositionTrackAudio insertTimeRange:_videoFullRange ofTrack:audioTrack atTime:kCMTimeZero error:&error] )
            NSLog(@"%@", error);

        _compositionTrackVideoA = [compositionTrackVideoA copy];
        _compositionTrackVideoB = [compositionTrackVideoB copy];

        AVPlayerItem * playerItem = [AVPlayerItem playerItemWithAsset:composition];

        AVPlayer * player = [AVPlayer playerWithPlayerItem:playerItem];

        [(AVPlayerLayer *)self.layer setPlayer:player];

        [player play];

        [player addObserver:self forKeyPath:@"status" options:0 context:0];

        [self updateCompositionForPlayerItem:playerItem];

        UITapGestureRecognizer * tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(didTap:)];
        [self addGestureRecognizer:tapGesture];
    
    return self;


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

    if ( [keyPath isEqualToString:@"status"] )
        NSLog(@"STATUS %d", ((AVPlayer *)object).status );


- (void)updateCompositionForPlayerItem:(AVPlayerItem *)playerItem


    AVMutableVideoComposition * videoComposition = [AVMutableVideoComposition videoComposition];

    AVMutableVideoCompositionInstruction *videoInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    videoInstruction.enablePostProcessing = NO;
    videoInstruction.timeRange = _videoFullRange;

    AVMutableVideoCompositionLayerInstruction * layerInstructionA = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:_compositionTrackVideoA];
    CGAffineTransform transformA = CGAffineTransformMakeScale(0.5, 0.5);
    [layerInstructionA setTransform:transformA atTime:kCMTimeZero];
    AVMutableVideoCompositionLayerInstruction * layerInstructionB = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:_compositionTrackVideoB];
    CGAffineTransform transformB = CGAffineTransformMakeScale(0.5, 0.5);
    static int i = 0;
    transformB = CGAffineTransformTranslate(transformB, (i++ % 2 == 0) ? _videoSize.width : 0, _videoSize.height);
    [layerInstructionB setTransform:transformB atTime:kCMTimeZero];

    videoInstruction.layerInstructions = [NSArray arrayWithObjects:layerInstructionA, layerInstructionB, nil];

    videoComposition.instructions = [NSArray arrayWithObject:videoInstruction];

    videoComposition.frameDuration = CMTimeMake(1, 30); // 30 fps
    videoComposition.renderSize = _videoSize;

    playerItem.videoComposition = videoComposition;



- (void)didTap:(UITapGestureRecognizer *)tapGesture

    [self updateCompositionForPlayerItem:((AVPlayerLayer *)self.layer).player.currentItem];


@end

【问题讨论】：

这个问题你解决了吗？

【参考方案1】：

您可以节省要更改它的时间，并用新的视频合成替换播放器项目，然后从您停止播放的时间开始用新的播放器项目重新启动播放器。

【讨论】：

这是一个明显的解决方法，但它有一个视觉上的“打嗝”。它只是无法正常进行。