如何在AVPlayerItemVideoOutput中使用AVPlayerLooper？

Question

AVPlayerLooper接受模板AVPlayerItem和AVQueuePlayer作为设置参数，然后在内部操作队列的项，播放器不断更改其currentItem。

这在AVPlayerLayer中工作得很好，它接受这个循环播放器作为参数并只是渲染它，但是我如何在AVPlayerItemVideoOutput中使用它，它被附加到AVPlayerItem，播放器内部有多个？如何在内部重现AVPlayerLayer所做的相同事情？

文档中的AVPlayerLooper设置示例

NSString *videoFile = [[NSBundle mainBundle] pathForResource:@"example" ofType:@"mov"];
NSURL *videoURL = [NSURL fileURLWithPath:videoFile];

_playerItem = [AVPlayerItem playerItemWithURL:videoURL];
_player = [AVQueuePlayer queuePlayerWithItems:@[_playerItem]];
_playerLooper = [AVPlayerLooper playerLooperWithPlayer:_player templateItem:_playerItem];
_playerLayer = [AVPlayerLayer playerLayerWithPlayer:_player];
_playerLayer.frame = self.view.bounds;
[self.view.layer addSublayer:_playerLayer];
[_player play];

这就是AVPlayerItemVideoOutput的用法

[item addOutput:_videoOutput];

我想出的唯一解决办法是观察currentItem的变化，每次从旧项目中分离视频输出并将其附加到新项目，如下面的示例，但这显然中和了我试图实现的无缝回放。

- (void)observeValueForKeyPath:(NSString*)path
                      ofObject:(id)object
                        change:(NSDictionary*)change
                       context:(void*)context {
   if (context == currentItemContext) {
      AVPlayerItem* newItem = [change objectForKey:NSKeyValueChangeNewKey];
      AVPlayerItem* oldItem = [change objectForKey:NSKeyValueChangeOldKey];
      if(oldItem.status == AVPlayerItemStatusReadyToPlay) {
          [newItem removeOutput:_videoOutput];
      }
      if(newItem.status == AVPlayerItemStatusReadyToPlay) {
          [newItem addOutput:_videoOutput];
      }
      [self removeItemObservers:oldItem];
      [self addItemObservers:newItem];
   }
}

为了了解更多上下文，我正在尝试为flutter的video_player插件https://github.com/flutter/flutter/issues/72878提供一个修复方案

插件的代码可以在这里找到https://github.com/flutter/plugins/blob/172338d02b177353bf517e5826cf6a25b5f0d887/packages/video_player/video_player/ios/Classes/FLTVideoPlayerPlugin.m

Answer 1

您可以通过将AVQueuePlayer子类化(yay OOP)并根据需要在其中创建和添加AVPlayerItemVideoOutput来实现这一点。我以前从未见过多个AVPlayerItemVideoOutput，但内存消耗似乎很合理，一切都正常。

@interface OutputtingQueuePlayer : AVQueuePlayer
@end

@implementation OutputtingQueuePlayer

- (void)insertItem:(AVPlayerItem *)item afterItem:(nullable AVPlayerItem *)afterItem;
{
    if (item.outputs.count == 0) {
        NSLog(@"Creating AVPlayerItemVideoOutput");
        AVPlayerItemVideoOutput *videoOutput = [[AVPlayerItemVideoOutput alloc] initWithOutputSettings:nil]; // or whatever
        [item addOutput:videoOutput];
    }
    [super insertItem:item afterItem:afterItem];
}
@end

当前输出的访问方式如下：

AVPlayerItemVideoOutput *videoOutput = _player.currentItem.outputs.firstObject;
CVPixelBufferRef pixelBuffer = [videoOutput copyPixelBufferForItemTime:_player.currentTime itemTimeForDisplay:nil];
// do something with pixelBuffer here
CVPixelBufferRelease(pixelBuffer);

配置就变成了：

_playerItem = [AVPlayerItem playerItemWithURL:videoURL];
_player = [OutputtingQueuePlayer queuePlayerWithItems:@[_playerItem]];
_playerLooper = [AVPlayerLooper playerLooperWithPlayer:_player templateItem:_playerItem];
_playerLayer = [AVPlayerLayer playerLayerWithPlayer:_player];
[self.view.layer addSublayer:_playerLayer];
[_player play];