知道 AVPlayer 对象何时准备好播放 [英] Knowing when AVPlayer object is ready to play

问题描述

我正在尝试播放一个 MP3 文件，该文件从之前的 UIView(存储在 NSURL *fileURL 变量).

I'm trying to play an MP3 file that is passed to an UIView from a previous UIView (stored in a NSURL *fileURL variable).

我正在初始化一个 AVPlayer:

player = [AVPlayer playerWithURL:fileURL];

NSLog(@"Player created:%d",player.status);

NSLog 打印 Player created:0, 我认为这意味着它还没有准备好播放.

The NSLog prints Player created:0, which i figured means it is not ready to play yet.

当我点击播放UIButton时，我运行的代码是:

When i click the play UIButton, the code i run is:

-(IBAction)playButtonClicked
{
    NSLog(@"Clicked Play. MP3:%@",[fileURL absoluteString]);

    if(([player status] == AVPlayerStatusReadyToPlay) && !isPlaying)
//  if(!isPlaying)
    {
        [player play];
        NSLog(@"Playing:%@ with %d",[fileURL absoluteString], player.status);
        isPlaying = YES;
    }
    else if(isPlaying)
    {

        [player pause];
        NSLog(@"Pausing:%@",[fileURL absoluteString]);
        isPlaying = NO;
    }
    else {
        NSLog(@"Error in player??");
    }

}

当我运行它时，我总是在控制台中收到 Error in player??.然而，如果我用一个简单的 if(!isPlaying)... 替换检查 AVPlayer 是否准备好播放的 if 条件，然后音乐播放第二次我点击播放UIButton.

When i run this, I always get Error in player?? in the console. If i however replace the if condition that checks if AVPlayer is ready to play, with a simple if(!isPlaying)..., then the music plays the SECOND TIME I click on the play UIButton.

控制台日志是:

Clicked Play. MP3:http://www.nimh.nih.gov/audio/neurogenesis.mp3
Playing:http://www.nimh.nih.gov/audio/neurogenesis.mp3 **with 0**

Clicked Play. MP3:http://www.nimh.nih.gov/audio/neurogenesis.mp3
Pausing:http://www.nimh.nih.gov/audio/neurogenesis.mp3

Clicked Play. MP3:http://www.nimh.nih.gov/audio/neurogenesis.mp3
2011-03-23 11:06:43.674 Podcasts[2050:207] Playing:http://www.nimh.nih.gov/audio/neurogenesis.mp3 **with 1**

我看到第二次，player.status 似乎持有 1，我猜是 AVPlayerReadyToPlay.

I see that the SECOND TIME, the player.status seems to hold 1, which I'm guessing is AVPlayerReadyToPlay.

在我第一次点击播放 UIButton 时，我该怎么做才能让播放正常工作?(即，我如何确保 AVPlayer 不仅已创建，而且还可以播放?)

What can I do to have the playing to work properly the first time i click the play UIButton? (ie, how can i make sure the AVPlayer is not just created, but also ready to play?)

推荐答案

您正在播放远程文件.AVPlayer 可能需要一些时间来缓冲足够的数据并准备好播放文件(请参阅 AV 基础编程指南)

You are playing a remote file. It may take some time for the AVPlayer to buffer enough data and be ready to play the file (see AV Foundation Programming Guide)

但是您似乎没有等待播放器准备就绪才点击播放按钮.我想要的是禁用此按钮并仅在播放器准备就绪时启用它.

But you don't seem to wait for the player to be ready before tapping the play button. What I would to is disable this button and enable it only when the player is ready.

使用 KVO，可以收到玩家状态变化的通知:

Using KVO, it's possible to be notified for changes of the player status:

playButton.enabled = NO;
player = [AVPlayer playerWithURL:fileURL];
[player addObserver:self forKeyPath:@"status" options:0 context:nil];   

状态改变时会调用这个方法:

This method will be called when the status changes:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
                        change:(NSDictionary *)change context:(void *)context {
    if (object == player && [keyPath isEqualToString:@"status"]) {
        if (player.status == AVPlayerStatusReadyToPlay) {
            playButton.enabled = YES;
        } else if (player.status == AVPlayerStatusFailed) {
            // something went wrong. player.error should contain some information
        }
    }
}

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