v4l2 - Where does v4l2_buffer->timestamp value starts counting? - Stack Overflow

#include <time.h>
#include <math.h>

//////////////////////
//setup: 

    long getEpochTimeShift(){
        struct timeval epochtime;
        struct timespec  vsTime;

        gettimeofday(&epochtime, NULL);
        clock_gettime(CLOCK_MONOTONIC, &vsTime);

        long uptime_ms = vsTime.tv_sec* 1000 + (long)  round( vsTime.tv_nsec/ 1000000.0);
        long epoch_ms =  epochtime.tv_sec * 1000  + (long) round( epochtime.tv_usec/1000.0);
        return epoch_ms - uptime_ms;
    }

    //stick this somewhere so that it runs once, on the startup of your capture process
    //  noting, if you hibernate a laptop, you might need to recalc this if you don't restart 
    //  the process after dehibernation
    long toEpochOffset_ms = getEpochTimeShift();


//////////////////////
//...somewhere in your capture loop: 

    struct v4l2_buffer buf;

    //make the v4l call to  xioctl(fd, VIDIOC_DQBUF, &buf)

    //then: 
    long temp_ms = 1000 * buf.timestamp.tv_sec + (long) round(  buf.timestamp.tv_usec / 1000.0);
    long epochTimeStamp_ms = temp_ms + toEpochOffset_ms ;

    printf( "the frame's timestamp in epoch ms is: %ld", epochTimeStamp_ms);