1、图片转视频流（CVPixelBufferRef）

// image convert to Pixel buffer
- (CVPixelBufferRef)pixelBufferFromCGImage:(CGImageRef)image
                                      size:(CGSize)imageSize
{
    NSDictionary *options = @{(id)kCVPixelBufferCGImageCompatibilityKey: @YES,
                              (id)kCVPixelBufferCGBitmapContextCompatibilityKey: @YES};
    CVPixelBufferRef pxbuffer = NULL;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, imageSize.width,
                                          imageSize.height, 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, imageSize.width,
                                                 imageSize.height, 8, 4*imageSize.width, rgbColorSpace,
                                                 kCGImageAlphaNoneSkipFirst);
    NSParameterAssert(context);

    CGContextDrawImage(context, CGRectMake(0 + (imageSize.width-CGImageGetWidth(image))/2,
                                           (imageSize.height-CGImageGetHeight(image))/2,
                                           CGImageGetWidth(image),
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}

2、视频流（CVImageBufferRef）转图片

// CVImageBufferRef to UIImage
- (UIImage *)screenshotOfVideoStream:(CVImageBufferRef)imageBuffer
{
    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuffer];
    CIContext *temporaryContext = [CIContext contextWithOptions:nil];
    CGImageRef videoImage = [temporaryContext
                             createCGImage:ciImage
                             fromRect:CGRectMake(0, 0,
                                                 CVPixelBufferGetWidth(imageBuffer),
                                                 CVPixelBufferGetHeight(imageBuffer))];

    UIImage *image = [[UIImage alloc] initWithCGImage:videoImage];
    CGImageRelease(videoImage);
    return image;
}

3、视频流（CVImageBufferRef）转图片

+ (UIImage *)trasformToImageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8,
                                                 bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);
    
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    UIImage *image = [UIImage imageWithCGImage:quartzImage scale:1.0 orientation:UIImageOrientationRight];
    
    CGImageRelease(quartzImage);
    return (image);
}

拓展：

借鉴：深入理解 CVPixelBufferRef
https://zhuanlan.zhihu.com/p/24762605