对于HTTP直播，iOS AVAsset.duration为零，但适用于渐进式 [英] iOS AVAsset.duration is zero for HTTP live streaming but works for progressive

问题描述

我有一个iOS应用程序，可以播放来自HTTP Live流playlist.m3u8的视频，我有一个使用AVPlayer创建的自定义播放器。为了处理正常的用户交互，例如擦洗，我需要获取视频的持续时间，但出于某种原因，在使用xcode 4.0的iOS 4.3上，当我调用以下代码时，我得到一个CMTime，当转换为秒时给出一个NaN - 我知道它正在做什么，因为CMTimeValue = 0和CMTimeScale = 0，它给出NaN和CMTimeFlags = 17，这更奇怪。

I have an iOS app that plays video from a HTTP Live stream "playlist.m3u8" and I have a custom player created using AVPlayer. To handle normal user interactions such as scrubbing i need to get the duration of the video, but for some reason on iOS 4.3 using xcode 4.0 when I call the following code I get a CMTime that when converted to seconds gives a NaN -- I know what it's doing because CMTimeValue = 0 and CMTimeScale = 0 which gives the NaN and the CMTimeFlags = 17 which is even more strange.

这是我使用的代码不是复杂的：

Here's the code I uses which isn't complex at all:

AVPlayerItem *pItem = mPlayer.currentItem;
AVAsset* asset = pItem.asset;
CMTime d = asset.duration;
double duration = CMTimeGetSeconds(asset.duration);

我还应该提一下，我确实监控加载播放列表的状态，以确保它在我之前准备就绪开始播放/擦洗：

I should also mention that I do monitor the status of the loading playlist to make sure it's ready before i start playing/scrubbing:

[mPlayer addObserver:self forKeyPath:@"currentItem.status" options:0 context:VideoPlaybackViewDelegateStatusContext];

感谢您对此问题的任何帮助。

Thanks for any help on this issues anyone could provide.

推荐答案

https://developer.apple.com/library/ios/releasenotes/AudioVideo/RN-AVFoundation-Old/#//apple_ref/doc/uid/TP40011199 -CH1-SW4

上面提到的文档现在应该从 AVPlayerItem 实例中获取持续时间，而不是相应的 AVAsset 。为了通过键值观察获得当前玩家项目的持续时间，我使用以下方法（最初来自 NGMoviePlayer 是为iOS 4.0编写的：

The docs above mention that duration should now be obtained from the AVPlayerItem instance, rather than its corresponding AVAsset. To get the duration from the current player item via key-value observing, I use the following method (originally pulled from NGMoviePlayer which was written for iOS 4.0):

- (void)loadPlayerWithItem:(AVPlayerItem *)playerItem {
    self.player = [AVPlayer playerWithPlayerItem:playerItem];
    ...
    // changed this from previous value currentItem.asset.duration
    [self.player addObserver:self forKeyPath:@"currentItem.duration"
                                     options:0
                                     context:nil];
    ...
}

我在播放器中实现了上述更改持续时间现在正在运作！ AVFoundation的这一变化是该问题的根本原因。 CMTimeFlags = 17表示kCMTimeFlags_Indefinite& kCMTimeFlags_Valid，以及 docs 指定：

I implemented the above change in my player and the duration is working now! This change in AVFoundation was the root cause of the issue. CMTimeFlags = 17 indicates kCMTimeFlags_Indefinite & kCMTimeFlags_Valid, and the docs specify:

特别是，URL资产为基于流媒体的媒体报告的持续时间是通常为kCMTimeIndefinite，而相应的AVPlayerItem的持续时间可能不同，并且可能会在播放时发生变化。

In particular, the duration reported by the URL asset for streaming-based media is typically kCMTimeIndefinite, while the duration of a corresponding AVPlayerItem may be different and may change while it plays.

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