arpo arpo - 2 months ago 26
Swift Question

Grab frames from video using Swift

I want to grab frames from a video at a specific time. I'm calling my grab-frame-function with a time specified as seconds as a Float64.
The problem is that it doesn't grab the current frame. It seems to ignore the decimals. If I call the function with for example 1.22 and 1.70 it will return the same frame. I'm quite new when it comes to Swift so I guess I don't get the CMTime object right. So can anyone see what's wrong with this?

func generateThumnail(url : NSURL, fromTime:Float64) -> UIImage {
var asset :AVAsset = AVAsset.assetWithURL(url) as! AVAsset
var assetImgGenerate : AVAssetImageGenerator = AVAssetImageGenerator(asset: asset)
assetImgGenerate.appliesPreferredTrackTransform = true
var error : NSError? = nil
var time : CMTime = CMTimeMakeWithSeconds(fromTime, 600)
var img : CGImageRef = assetImgGenerate.copyCGImageAtTime(time, actualTime: nil, error: &error)
var frameImg : UIImage = UIImage(CGImage: img)!
return frameImg
}

var grabTime = 1.22
img = generateThumnail(urlVideo, fromTime: Float64(grabTime))

Answer

Thanks to @eric-d who found this post: iOS Take Multiple Screen Shots

I manage to find out that adding:

    assetImgGenerate.requestedTimeToleranceAfter = kCMTimeZero;
    assetImgGenerate.requestedTimeToleranceBefore = kCMTimeZero;

...to my function will do the trick.

My updated function looks like this:

func generateThumnail(url : NSURL, fromTime:Float64) -> UIImage {
    var asset :AVAsset = AVAsset.assetWithURL(url) as! AVAsset
    var assetImgGenerate : AVAssetImageGenerator = AVAssetImageGenerator(asset: asset)
    assetImgGenerate.appliesPreferredTrackTransform = true
    assetImgGenerate.requestedTimeToleranceAfter = kCMTimeZero;
    assetImgGenerate.requestedTimeToleranceBefore = kCMTimeZero;
    var error       : NSError? = nil
    var time        : CMTime = CMTimeMakeWithSeconds(fromTime, 600)        
    var img         : CGImageRef = assetImgGenerate.copyCGImageAtTime(time, actualTime: nil, error: &error)
    var frameImg    : UIImage = UIImage(CGImage: img)!
    return frameImg
}

var grabTime = 1.22
img = generateThumnail(urlVideo, fromTime: Float64(grabTime))