CMTimeCompare是如何工作的？

Question

CMTimeCompare是如何工作的？苹果似乎在他们的文档中省略了返回值。

https://developer.apple.com/library/mac/#documentation/CoreMedia/Reference/CMTime/Reference/reference.html

我假设如果时间相等，则返回零，并根据哪个更大返回正数或负数1？

- Dex

Answer 1

从CMTime.h文件:

返回两个CMTimes的数字关系（-1 = less than，1 = greater than，0 = equal）。

如果time1小于time2，则返回-1。 如果它们相等，则返回0。 如果time1大于time2，则返回1。

编辑：

请注意：

无效的CMTimes被视为与其他无效的CMTimes相等，并且大于任何其他CMTime。正无穷被认为小于任何无效的CMTime、等于自身并且大于任何其他CMTime。一个不确定的CMTime被认为比任何无效的CMTime小，比正无穷小，等于自身，并且大于任何其他CMTime。负无穷被认为等于自身，并且小于任何其他CMTime。

- fbernardo

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如果我执行 CMTimeCompare(a, b)，它会返回 -1 如果 a < b 吗？ - Dex

Answer 2

如果您希望一种比CMTimeCompare（）更易读的替代方案，请考虑使用CMTIME_COMPARE_INLINE宏。例如：

CMTIME_COMPARE_INLINE(time1, <=, time2)

如果 time1 <= time2，则返回 true

- bcattle

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很遗憾，CMTIME_COMPARE_INLINE在Swift中尚不可用。 - adriaan

Answer 3

这是用 AVPlayerItem 的 .currentTime() 和 .duration 在 Swift 5 中的非常简单的解释。

let videoCurrentTime = playerItem.currentTime() // eg. the video is at the 30 sec point
let videoTotalDuration = playerItem.duration // eg. the video is 60 secs long in total

// 1. this will be false because if the videoCurrentTime is at 30 and it's being compared to the videoTotalDuration which is 60 then they are not equal.
if CMTimeCompare(videoCurrentTime, videoTotalDuration) == 0 { // 0 means equal

    print("do something")
    // the print statement will NOT run because this is NOT true
    // it is the same thing as saying: if videoCurrentTime == videoCurrentTime { do something }
}

// 2. this will be true because if the videoCurrentTime is at 30 and it's being compared to the videoTotalDuration which is 60 then they are not equal.
if CMTimeCompare(videoCurrentTime, videoTotalDuration) != 0 { // != 0 means not equal

    print("do something")
    // the print statement WILL run because it IS true
    // this is the same thing as saying: if videoCurrentTime != videoTotalDuration { do something }
}

// 3. this will be true because if the videoCurrentTime is at 30 and it's being compared to 0 then 30 is greater then 0
if CMTimeCompare(videoCurrentTime, .zero) == 1 { // 1 means greater than

    print("do something")
    // the print statement WILL run because it IS true
    // this is the same thing as saying: if videoCurrentTime > 0 { do something }
}

// 4. this will be true because if the videoCurrentTime is at 30 and it's being compared to the videoTotalDuration which is 60 then 30 is less than 60
if CMTimeCompare(videoCurrentTime, videoTotalDuration) == -1 { // -1 means less than

    print("do something")
    // the print statement WILL run because it IS true
    // this is the same thing as saying: if videoCurrentTime < videoTotalDuration { do something }
}

- Lance Samaria