视频开发相关问题

一、CMTimeMake和CMTimeMakeWithSeconds 区别

CMTimeMake(a,b)    a当前第几帧, b每秒钟多少帧.当前播放时间a/b 

CMTimeMakeWithSeconds(a,b)    a当前时间,b每秒钟多少帧.

 1) 

Float64 seconds = 5; 
int32_t preferredTimeScale = 600;
CMTime inTime = CMTimeMakeWithSeconds(seconds, preferredTimeScale);
CMTimeShow(inTime);
 The above code gives: {3000/600 = 5.000} 
 Which means a total duration of 5 seconds, with 3000 frames with a timescale of 600 frames per second. 
 2) 
int64_t value = 10000;
int32_t preferredTimeScale = 600;
CMTime inTime = CMTimeMake(value, preferredTimeScale);
CMTimeShow(inTime);
 This one gives {10000/600 = 16.667} 
 Which means a total duration of 16.667 seconds, with 10000 frames with a timescale of 600 frames per second. 
 Notice the difference between CMTimeMake(int64_t value, int32_t timescale) and CMTimeMakeWithSeconds(Float64 seconds, int32_t preferredTimeScale)