AVFoundation视频处理的时间CMTime

一、CMTime

Core Media定义的一种时间数据类型

typedef struct
{
    CMTimeValue value;  //64位有符号整型变量，作为分子
    CMTimeScale timescale;   //32位有符号整型变量，作为分母
    // value/timescale = 对应时间-秒
    CMTimeFlags flags; //位掩码，表示时间的指定状态，比如判定诗句是否有效、不确定或是是否出现舍入等
    CMTimeEpoch epoch;      
} CMTime;

1、创建CMTime

• 1、CMTimeMake()
  CMTime CMTimeMake(
int64_t value,int32_t timescale)

创建一个代表3秒的CMTime表达式(value/timescale)：

CMTime ts1 = CMTimeMake(3, 1);
CMTime ts2 = CMTimeMake(1800, 600);
CMTime ts3 = CMTimeMake(132300, 44100);

//打印时间结果
CMTimeShow(ts1);
CMTimeShow(ts2);
CMTimeShow(ts3);

//打印结果
{3/1 = 3.000}
{1800/600 = 3.000}
{132300/44100 = 3.000}

在处理视频内容时常见的时间刻度为600，这是大部分常用视频帧率24FPS、25FPS、30FPS的公倍数。音频常见的时间刻度就是采样率，如44.1kHz(44100)、48kHz(48000)。

• 2、CMTimeMakeWithSeconds()

CMTime CMTimeMakeWithSeconds(
Float64 seconds,
int32_t preferredTimescale)

CMTime t = CMTimeMakeWithSeconds(5, 1); // 5 seconds

CMTimeShow(t);
//{5/1 = 5.000}

• 3、CMTimeMakeFromDictionary

NSDictionary *timeData = @{(id)kCMTimeValueKey : @2,
                           (id)kCMTimeScaleKey : @1,
                           (id)kCMTimeFlagsKey : @1,
                           (id)kCMTimeEpochKey : @0};
CMTime t = CMTimeMakeFromDictionary((__bridge CFDictionaryRef)timeData); 

CMTimeShow(t);
//{2/1 = 2.000}

2、CMTime运算

• 1、加减

CMTime ts1 = CMTimeMake(3, 1);
CMTime ts2 = CMTimeMake(5, 2);

CMTime result;
result = CMTimeAdd(ts1, ts2);
CMTimeShow(result);
//{11/2 = 5.500}

result = CMTimeSubtract(ts1, ts2);
CMTimeShow(result);
//{1/2 = 0.500}

• 2、比较

CMTime t1 = CMTimeMake(300, 100); // 3 seconds
CMTime t2 = CMTimeMakeWithSeconds(5, 1); // 5 seconds

CMTimeCompare()

int32_t r  = CMTimeCompare(t1, t2);
NSLog(@"compare: %d",r);
//t1 < t2   => -1
//t1 == t2  => 0
//t1 > ts   => 1

CMTIME_COMPARE_INLINE()

NSLog(@"t1 > t2 => %@",CMTIME_COMPARE_INLINE(t1, >, t2) ? @"YES":@"NO");
// t1 > t2 => NO

• 3、验证CMTIME_IS_VALID()

NSLog(@"ti is valid :%@",CMTIME_IS_VALID(t1) ? @"YES":@"NO");
// ti is valid :YES

3、CMTime转换为秒

Float64 CMTimeGetSeconds(
CMTime time)

CMTime t1 = CMTimeMake(3001, 100);
NSLog(@"second : %f",CMTimeGetSeconds(t1));
//second : 30.010000

4、转换为对象NSValue

+ (NSValue *)valueWithCMTime:(CMTime)time;

CMTime structTime = CMTimeMake(1, 3);

NSValue *valueTime = [NSValue valueWithCMTime:structTime];
NSLog(@"%@", valueTime);
//CMTime: {1/3 = 0.333}

structTime = [valueTime CMTimeValue];
CMTimeShow(structTime);
//{1/3 = 0.333}

5、转换字典NSDictionary

 CMTime structTime = CMTimeMake(1, 3);
NSDictionary *timeDict = CFBridgingRelease(CMTimeCopyAsDictionary(structTime, NULL));
NSLog(@"%@", timeDict);

structTime = CMTimeMakeFromDictionary((__bridge CFDictionaryRef)(timeDict));
CMTimeShow(structTime);

/*
 {
    epoch = 0;
    flags = 1;
    timescale = 3;
    value = 1;
}
{1/3 = 0.333}

*/

二、CMTimeRange

时间范围的数据类型：CMTimeRange，由两个CMTime值组成，第一个定义时间范围的起点，第二个定义时间范围的持续时间。

typedef struct
{
    CMTime          start;
    CMTime          duration;
} CMTimeRange;

1、创建

• 1、CMTimeRangeMake()

CMTimeRange CMTimeRangeMake(
CMTime start,
CMTime duration)
根据开始时间点与持续时间确定时间范围。

//创建一个时间范围，从时间轴的5秒位置开始，持续时长5秒
CMTime duration = CMTimeMake(5, 1);
CMTimeRange range = CMTimeRangeMake(duration, duration);
CMTimeRangeShow(range);

//{{5/1 = 5.000}, {5/1 = 5.000}}

• 2、CMTimeRangeFromTimeToTime()

CMTimeRange CMTimeRangeFromTimeToTime(
CMTime start,
CMTime end )
根据起始时间点和终止时间点，确定时间范围。

CMTime beginTime = CMTimeMake(5, 1);
CMTime endTime = CMTimeMake(12, 1);
CMTimeRange rangeTime = CMTimeRangeFromTimeToTime(beginTime, endTime);
CMTimeRangeShow(rangeTime);
//{{5/1 = 5.000}, {7/1 = 7.000}}

2、运算

定义变量：

CMTime duration = CMTimeMake(5, 1);
CMTimeRange range = CMTimeRangeMake(duration, duration);
CMTimeRangeShow(range);
//{{5/1 = 5.000}, {5/1 = 5.000}}

CMTime beginTime = CMTimeMake(7, 1);
CMTime endTime = CMTimeMake(12, 1);
CMTimeRange rangeTime = CMTimeRangeFromTimeToTime(beginTime, endTime);
CMTimeRangeShow(rangeTime);
//{{7/1 = 7.000}, {5/1 = 5.000}}

取交叉时间范围

CMTimeRange intersetionRange = CMTimeRangeGetIntersection(range, rangeTime);
CMTimeRangeShow(intersetionRange);
//{{7/1 = 7.000}, {3/1 = 3.000}}

取时间范围总和

CMTimeRange unionRange = CMTimeRangeGetUnion(range, rangeTime);
    CMTimeRangeShow(unionRange);
//{{5/1 = 5.000}, {7/1 = 7.000}}

3、转换为对象NSValue

+ (NSValue *)valueWithCMTimeRange:(CMTimeRange)timeRange

CMTimeRange structTimeRange = CMTimeRangeMake(kCMTimeZero, kCMTimePositiveInfinity);

NSValue *valueTimeRange = [NSValue valueWithCMTimeRange:structTimeRange];
NSLog(@"%@", valueTimeRange);
//CMTimeRange: {{0/1 = 0.000}, {+INFINITY}}

structTimeRange = [valueTimeRange CMTimeRangeValue];
CMTimeRangeShow(structTimeRange);
//{{0/1 = 0.000}, {+INFINITY}}

4、转换成字典NSDictionary

NSDictionary *timeRangeDict = CFBridgingRelease(CMTimeRangeCopyAsDictionary(structTimeRange, NULL));
NSLog(@"%@", timeRangeDict);

structTimeRange = CMTimeRangeMakeFromDictionary((__bridge CFDictionaryRef)(timeRangeDict));
CMTimeRangeShow(structTimeRange);

/*
 {
    duration =     {
        epoch = 0;
        flags = 5;
        timescale = 0;
        value = 0;
    };
    start =     {
        epoch = 0;
        flags = 1;
        timescale = 1;
        value = 0;
    };
}
{{0/1 = 0.000}, {+INFINITY}}
*/