Make CMTime with a very small value

问题:

I have a small integer value and I want to convert it into CMTime.

The problem is that

CMTime(value: _ , timeScale: _)

or

CMTimeMakeWithSeconds(value: _ , timeScale: _)

will always return the floor so that time always equals 0.0 seconds

let smallValue = 0.0401588716
let frameTime = CMTime(Int64(smallValue) , timeScale: 1) 
//frameTime is 0.0 seconds because of Int64 conversion

let frameTimeInSeconds = CMTimeMakeWithSeconds(smallValue , timeScale: 1) 
// frameTimeInSeconds also returns 0.0 seconds.

回答1:

CMTime represents a time value as a rational number with integer numerator (the value) and denominator (the timescale) . In order to represent a small value like yours, you have to choose a larger timescale (depending on the desired accuracy). Example:

let smallValue = 0.0401588716
let frameTime = CMTime(seconds: smallValue, preferredTimescale: 1000000) 

print(frameTime.seconds) // 0.040158

回答2:

I should have put a little thought into it before posting the question.

 let smallValue =  0.0401588716
 let oneSec =      CMTimeMakeWithSeconds(1, timeScale: 1) 
 let frameTime =   CMTimeMultiplyByFloat64(oneSec , smallValue)
 print(CMTimeGetSeconds(frameTime))                              //  0.040158872