iphone- [AVAssetReaderAudioMixOutput copyNextSampleBuffer] Error
<p>I am working with AVAssetReader and AVAssetWriter to make movie with multi tracks.
So I finished it using [AVAssetReaderAudioMixOutput copyNextSampleBuffer] and [AVAssetWriterInput appendSampleBuffer].</p>

<p>But I kept getting the error: [AVAssetReaderTrackOutput copyNextSampleBuffer] cannot copy next sample buffer unless the asset reader is in the 'reading' state'.
How solve this problem.</p>
