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

Question

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)。似乎有时这行得通，并且视频合成无缝地更改为新的变换集，但其他时候它只是卡住并保持当前变换。 AVPlayer 实例上没有状态代码更改，播放器或播放器项目上也没有错误。

有没有人遇到过这种情况？任何关于为什么会发生这种情况或如何解决它的建议，我们将不胜感激。

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

此问题的另一种解决方案是在单独的图层上显示视频，但视频必须同步，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

Answer 1

您可以保存您想要更改它的时间，并用新的视频组合替换播放器项目，并从您停止播放的时间开始使用新的播放器项目重新启动播放器。