Question

CMTimeCompare如何运作？ Apple似乎已经从他们的文档中遗漏了返回值。

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返回正或负1，基于哪个更大？

Answer 1

来自 CMTime.h ：

返回数值关系（-1 =小于，1 =大于，   0 =相等）两个CMTime。
     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。

修改

请注意：

无效CMTime被认为等于其他无效CMTime，并且大于任何其他CMTime。正无穷大被认为小于任何无效的CMTime，等于自身，并且比任何其他CMTime都要大。考虑无限期CMTime 小于任何无效的CMTime，小于正无穷大，等于它自己，并且比任何其他CMTime都要大。负无穷大被认为等于自身，并且比任何其他CMTime少。

Answer 2

对于比CMTimeCompare()更容易阅读的替代方案，请考虑使用CMTIME_COMPARE_INLINE macro。例如

CMTIME_COMPARE_INLINE(time1, <=, time2)

如果time1＆lt; = time2

，

将返回true

Answer 3

在Swift 5中使用AVPlayerItem及其.currentTime()和.duration

进行了非常简单的解释

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 }
}

CMTimeCompare如何工作？

3 个答案: