如何将AVSampleBufferDisplayLayer中显示的数据另存为Gallery中的视频文件？

Question

我有这个委托方法，该方法不断向我提供CMSampleBufferRef并将其加入队列

-(void)sampleBufferReceived: 
   (CMSampleBufferRef)sampleBuffer
{
    CFArrayRef attachments = 
CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, YES);
    CFMutableDictionaryRef dict = 
(CFMutableDictionaryRef)CFArrayGetValueAtIndex(attachments, 0);
    CFDictionarySetValue(dict, 
kCMSampleAttachmentKey_DisplayImmediately, kCFBooleanTrue);
    [_sampleBufferLayer enqueueSampleBuffer:sampleBuffer];
    CFRelease(sampleBuffer);
}

如何将这些samplebufferref保存为图库中的视频文件？