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在使用iOS系统播放器AVPlayerController播放一段回放视频时，发现在开播之前，打印播放器的duration，按常理推测，打印应该是nil或者是0什么的，但是结果发现打印出来是nan，这是什么鬼？

看了下官方文档

This property is observable. The duration of an item can change dynamically during playback.

Unless you omit @"duration" from the array of asset keys you pass to +playerItemWithAsset:automaticallyLoadedAssetKeys: or
-initWithAsset:automaticallyLoadedAssetKeys:, the value of this property will accord with the properties of the underlying
AVAsset and the current state of playback once the receiver becomes ready to play.

Before the underlying duration has been loaded, the value of this property is kCMTimeIndefinite. Use key-value observation to
obtain a valid duration as soon as it becomes available. (Note that the value of duration may remain kCMTimeIndefinite,
e.g. for live streams.)

说此值在播放器开始播放之前是kCMTimeIndefinite:


Before the underlying duration has been loaded, the value of this property is kCMTimeIndefinite.


开始播放后才能拿到该值。但是

kCMTimeIndefinite

是什么？

官方文档kCMTimeIndefinite https://developer.apple.com/documentation/coremedia/kcmtimeindefinite?language=objc


CMTimeGetSeconds()

函数

当传入参数为nil时，返回nan

[992:467164] *****(null)******* nan
[992:467164] *****(null)******* nan
[992:467164] *****<AVPlayer: 0x1378a29d0>******* 0.000000
[992:466589] *****<AVPlayer: 0x1378a29d0>******* 0.000000

打印了播放器对象avPlayer和它的currentTime。当avPlayer为空时，currentTime为NULL，这个函数返回nan。