Need assistance regarding CMTimeMakeWithSeconds - ios

Question

I am trying to fetch all frames of video and converting and storing them as individual images.
I am using this code in AV Foundation Programming Guide.
the code for getting multiple images is
CMTime firstThird = CMTimeMakeWithSeconds(durationSeconds/3.0, 600);
CMTime secondThird = CMTimeMakeWithSeconds(durationSeconds*2.0/3.0, 600);
CMTime end = CMTimeMakeWithSeconds(durationSeconds, 600);
this is hard coded, but I want to convert whole video. I know I can use for loop but what to do with this durationsecond means how can I use from begging to end to get all frames?
here is my attempt
for(float f=0.0; f<=durationSeconds; f++) {
[times addObject:[NSValue valueWithCMTime:CMTimeMakeWithSeconds(durationSeconds, 600)]];
}

Answer 1

Any time you're about to write hundreds of lines of nearly identical code is probably a time where you need to be using a loop of some sort:
for (int currentFrame = 0; currentFrame < durationSeconds; ++currentFrame) {
CMTime currentTime = CMTimeMakeWithSeconds(i, 600);
// the rest of the code you need to create the image or whatever
}
That snippet will grab one frame per second. If you wanted to grab 30 frames per second, it'd look more like this:
const CGFloat framesPerSecond = 30.0;
for (int currentFrame = 0; currentFrame < (durationSeconds * framesPerSecond); ++currentFrame) {
CMTime currentTime = CMTimeMakeWithSeconds(currentFrame/framesPerSecond, 600);
// again, the code you need to create the image from this time
}
Just set the value of framesPerSecond to however many frames per second you want to capture.
As a disclaimer, I'm not completely familiar with this stuff, so a <= might be appropriate in the conditional statements here.
ADDENDUM: The code I've posted is only going to grab the timestamp for which to grab an image. The rest of the code should look something like this:
AVAsset *myAsset = // your asset here
AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:myAsset];
NSError *error;
CMTime actualTime;
CGImageRef currentImage = [imageGenerator copyCGImageAtTime:currentTime
actualTime:&actualTime
error:&error];
if (!error) {
[someMutableArray addObject:[[UIImage alloc] initWithCGImage:currentImage]];
}