使用Swift抓取视频中的帧 [英] Grab frames from video using Swift

问题描述

我想在特定时间从视频中抓取帧.我正在将我的抓取帧函数调用为Float64，将时间指定为秒. 问题在于它没有抓取当前帧.似乎忽略了小数点.如果我使用例如1.22和1.70调用该函数，它将返回同一帧.关于Swift，我是一个新手，所以我想我没有正确使用CMTime对象.那么谁能看到这是怎么回事?

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)) 

推荐答案

感谢@ eric-d找到了这篇文章: iOS进行多屏拍摄

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

我设法找出添加的内容:

I manage to find out that adding:

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

...对我的功能而言，它可以解决问题.

...to my function will do the trick.

我更新的功能如下:

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))

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