ASSETWriterInput for making Video from UIImages on Iphone Issues

I try the following 2 methods of appending UIImages pixelbuffer to ASSETWriterInput. Everything looks good except there's No data in the video file. What's wrong?

1 Adaptor class

AVAssetWriterInputPixelBufferAdaptor * avAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput sourcePixelBufferAttributes:NULL];

[avAdaptor appendPixelBufferixelBuffer withPresentationTime:CMTimeMake(1, 10)];

2 Making the

// Create sample buffer.
CMSampleBufferRef sampleBuffer = NULL;
result = CMSampleBufferCreateForImageBuffer(kCFAllocatorDef ault, pixelBuffer, true, NULL, NULL, videoInfo, &timing, &sampleBuffer);

// Ship out the frame.
NSParameterAssert(CMSampleBufferDataIsReady(sample Buffer));
NSParameterAssert([writerInput isReadyForMoreMediaData]);
BOOL success = [writerInput appendSampleBuffer:sampleBuffer];