iOS采取多个屏幕截图 [英] iOS Take Multiple Screen Shots

问题描述

我有一个包含视频的 NSURL ，我想要每秒钟记录该视频的一帧十次。我有代码，将捕获我的播放器的图像，但我有麻烦设置它捕获10帧每秒。我试着这样的东西，但它是返回相同的初始帧的视频，正确的次数？这是我有：

I have an NSURL that contains a video, and I want to record a frame of that video ten times every seconds. And I have code that will capture an image of my player, but I have trouble setting it up to take capture 10 frames per second. I am trying something like this, but it is returning the same initial frame of the video, the correct number of times? Here is what I have:

AVAsset *asset = [AVAsset assetWithURL:videoUrl];
CMTime vidLength = asset.duration;
float seconds = CMTimeGetSeconds(vidLength);
int frameCount = 0;
for (float i = 0; i < seconds;) {
    AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset];
    CMTime time = CMTimeMake(i, 10);
    CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:NULL];
    UIImage *thumbnail = [UIImage imageWithCGImage:imageRef];
                                CGImageRelease(imageRef);
NSString* filename = [NSString stringWithFormat:@"Documents/frame_%d.png", frameCount];
NSString* pngPath = [NSHomeDirectory() stringByAppendingPathComponent:filename];

[UIImagePNGRepresentation(thumbnail) writeToFile: pngPath atomically: YES];
frameCount++;
i = i + 0.1;
}

但是不是获取视频的当前时间i

But instead of getting the frame at the current time i of the video, I just get the initial frame?

如何获取视频的帧10次？

How can I get the frame of the video 10 times a second?

感谢您的帮助：）

推荐答案

您正在得到初始帧，因为您正试图创建CMTime帮助float value： / p>

You are getting initial frame because you are trying to create CMTime with help of float value:

CMTime time = CMTimeMake(i, 10);

由于 CMTimeMake 函数 int64_t 第一个参数，你的float值将被四舍五入到int，你会得到不正确的结果。

Since CMTimeMake function takes int64_t value as first parameter, your float value will be rounded to int, and you will get incorrect result.

让你的代码有点变化：

1）首先，您需要找到需要从视频中获取的总帧数。你写道你每秒需要10帧，因此代码将是：

1) At first, you need to find total frames count that you need to get from the video. You wrote that you need 10 frames per second, so the code will be:

int requiredFramesCount = seconds * 10;

2）接下来，您需要找到一个值，每个步骤的CMTime值：

2) Next you need to find a value that will be increasing your CMTime value on each step:

int64_t step = vidLength.value / requiredFramesCount;

3）最后，您需要将requestedTimeToleranceBefore和requestedTimeToleranceAfter设置为kCMTimeZero ，以在精确的时间获得框架：

3) And lastly, you need to set requestedTimeToleranceBefore and requestedTimeToleranceAfter to kCMTimeZero, to get a frame at precise time:

imageGenerator.requestedTimeToleranceAfter = kCMTimeZero;
imageGenerator.requestedTimeToleranceBefore = kCMTimeZero;

以下是代码的外观：

CMTime vidLength = asset.duration;
float seconds = CMTimeGetSeconds(vidLength);

int requiredFramesCount = seconds * 10;
int64_t step = vidLength.value / requiredFramesCount;

int value = 0;

for (int i = 0; i < requiredFramesCount; i++) {

    AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset];
    imageGenerator.requestedTimeToleranceAfter = kCMTimeZero;
    imageGenerator.requestedTimeToleranceBefore = kCMTimeZero;

    CMTime time = CMTimeMake(value, vidLength.timescale);

    CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:NULL];
    UIImage *thumbnail = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    NSString* filename = [NSString stringWithFormat:@"Documents/frame_%d.png", i];
    NSString* pngPath = [NSHomeDirectory() stringByAppendingPathComponent:filename];

    [UIImagePNGRepresentation(thumbnail) writeToFile: pngPath atomically: YES];

    value += step;
}

这篇关于iOS采取多个屏幕截图的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！