QuickTimeImplAvf.mm

// QuickTimeImplAvf.mm
// line 296

void MovieBase::seekToFrame( int frame )
{
    if( ! mPlayer )
        return;
    
    //CMTime currentTime = [mPlayer currentTime];
    //CMTime oneFrame = CMTimeMakeWithSeconds(1.0 / mFrameRate, currentTime.timescale); // ERROR, timescale=1
    
    // Plan A : Get correct timescale
    CMTime oneFrame = CMTimeMakeWithSeconds(1.0 / mFrameRate, mPlayer.currentItem.asset.duration.timescale );
    
  	// plan B : set timescale 600 manualy
    //CMTime oneFrame = CMTimeMakeWithSeconds(1.0 / mFrameRate, 600 );
    
    // plan C : Use frameRate
    //CMTime oneFrame = CMTimeMake(1, 20);
    
    CMTime startTime = kCMTimeZero;
    CMTime addedFrame = CMTimeMultiply(oneFrame, frame);
    CMTime added = CMTimeAdd(startTime, addedFrame);
    
    [mPlayer seekToTime:added toleranceBefore:kCMTimeZero toleranceAfter:kCMTimeZero];
}

CMTimeReference
https://developer.apple.com/library/mac/documentation/CoreMedia/Reference/CMTime/