iOS屏幕录制步骤一:截屏、将截屏图片合成视频

写在前面

公司近期让做一个录制屏幕类的App,我研究了iOS9新增的Replaykit框架,使用起来确实挺简单的,性能也很好,但是获取不到视频文件,这一点就决定了我不能使用这个框架。那么我只能使用最原始的方法,抓取view的截图,然后将这些截图合成视频,最后再把同时录制的音频合成到视频中。这篇文章先介绍如何抓取截图并合成视频。

抓取截屏

先贴一下代码:通过一个layer抓取屏幕截图

/// view => screen shot image
- (UIImage *)fetchScreenshot {
    UIImage *image = nil;
    if (self.captureLayer) {
        CGSize imageSize = self.captureLayer.bounds.size;
        UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
        CGContextRef context = UIGraphicsGetCurrentContext();
        [self.captureLayer renderInContext:context];
        image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
    
    return image;
}

上面的方法主要通过使用图形上下文CGContextRef来抓取layer的内容。代码很简单,不做过多的解释了。

将CGImage转换成CVPixelBufferRef缓存数据

/// image => PixelBuffer
- (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image {
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                             nil];
    
    CVPixelBufferRef pxbuffer = NULL;
    
    CGFloat frameWidth = CGImageGetWidth(image);
    CGFloat frameHeight = CGImageGetHeight(image);
    
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault,frameWidth,frameHeight,kCVPixelFormatType_32ARGB,(__bridge CFDictionaryRef) options, &pxbuffer);
    
    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
    
    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    NSParameterAssert(pxdata != NULL);
    
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, frameWidth, frameHeight, 8,CVPixelBufferGetBytesPerRow(pxbuffer),rgbColorSpace,(CGBitmapInfo)kCGImageAlphaNoneSkipFirst);
    
    NSParameterAssert(context);
    CGContextConcatCTM(context, CGAffineTransformIdentity);
    CGContextDrawImage(context, CGRectMake(0, 0,frameWidth,frameHeight),  image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    
    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
    
    return pxbuffer;
}

只有将CGImage转换成CVPixelBufferRef缓存数据后,才能存储到视频中。

将多张图片合成视频

将图片合成视频需要使用到以下几个类:

AVAssetWriter

AVAssetWriter负责将媒体数据写入到文件。创建AVAssetWriter对象需要传入的参数包括文件的输出路径URL和文件格式。文件格式选择AVFileTypeMPEG4即是MP4格式。

NSURL *fileUrl = [NSURL fileURLWithPath:self.videoPath];
    self.videoWriter = [[AVAssetWriter alloc] initWithURL:fileUrl fileType:AVFileTypeMPEG4 error:&error];
AVAssetWriterInput

AVAssetWriterInput负责存储视频或者音频缓存数据,AVAssetWriterInput对象创建完成后需要添加到AVAssetWriter中。

// 设置视频的编码和尺寸
NSDictionary *videoCompressionProps = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithDouble:size.width * size.height], AVVideoAverageBitRateKey, nil];
    
    NSDictionary *videoSettings = @{AVVideoCodecKey: AVVideoCodecH264,
                                    AVVideoWidthKey: @(size.width),
                                    AVVideoHeightKey: @(size.height),
                                    AVVideoCompressionPropertiesKey: videoCompressionProps};
    
    self.videoWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
    
    NSParameterAssert(self.videoWriterInput);

    // expectsMediaDataInRealTime设置为YES, 表示实时获取摄像头和麦克风采集到的视频数据和音频数据
    self.videoWriterInput.expectsMediaDataInRealTime = YES;
AVAssetWriterInputPixelBufferAdaptor

AVAssetWriterInputPixelBufferAdaptor负责将图片转成的缓存数据CVPixelBufferRef追加到AVAssetWriterInput中。

NSDictionary *bufferAttributes = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, nil];
    
    self.adaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:self.videoWriterInput sourcePixelBufferAttributes:bufferAttributes];

以上只写了图片合成视频的主要几个点,如果大家有不明白的,或者需要参考代码的话,请点击以下链接:GitHub

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