AVMutableAudioMix (Help!!!)

[Another]

Hi!
I want to make fade in/out effect for export session. But it doesn't work. Please help me!

NSURL *assetURL = [song valueForProperty:MPMediaItemPropertyAssetURL];	
	AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil];

AVAssetExportSession *exportSession = [[AVAssetExportSession alloc]
                                           initWithAsset:songAsset
                                           presetName:AVAssetExportPresetPassthrough];
	
	NSArray *tracks = [songAsset tracksWithMediaType:AVMediaTypeAudio];
	AVAssetTrack *track = [tracks objectAtIndex:0];
	id desc = [track.formatDescriptions objectAtIndex:0];
	const AudioStreamBasicDescription *audioDesc = CMAudioFormatDescriptionGetStreamBasicDescription((CMAudioFormatDescriptionRef)desc);
    FourCharCode formatID = audioDesc->mFormatID;


// trim track
	CMTime startTrimTime = CMTimeMakeWithSeconds(startTime, 1);
	CMTime endTrimTime = CMTimeMakeWithSeconds(endTime, 1);
	CMTimeRange exportTimeRange = CMTimeRangeFromTimeToTime(startTrimTime, endTrimTime);
	exportSession.timeRange = exportTimeRange;

//add fade in, fade out     
        CMTime startFadeInTime = startTrimTime;
        CMTime endFadeInTime = CMTimeMakeWithSeconds(startTime + 4.0, 1);
        CMTimeRange fadeInTimeRange = CMTimeRangeFromTimeToTime(startFadeInTime, endFadeInTime);
        
        CMTime startFadeOutTime = CMTimeMakeWithSeconds(endTime - 4.0, 1);
        CMTime endFadeOutTime = endTrimTime;
        CMTimeRange fadeOutTimeRange = CMTimeRangeFromTimeToTime(startFadeOutTime, endFadeOutTime);
         
        AVMutableAudioMix *exportAudioMix = [AVMutableAudioMix audioMix];
        
        //AVMutableAudioMixInputParameters *exportAudioMixInputParameters = [AVMutableAudioMixInputParameters audioMixInputParameters];
        AVMutableAudioMixInputParameters *exportAudioMixInputParameters = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:track];
        
        [exportAudioMixInputParameters setVolumeRampFromStartVolume:0.0 toEndVolume:1.0 timeRange:fadeInTimeRange];
        [exportAudioMixInputParameters setVolumeRampFromStartVolume:1.0 toEndVolume:0.0 timeRange:fadeOutTimeRange];

        exportAudioMix.inputParameters = [NSArray arrayWithObject:exportAudioMixInputParameters];       
        exportSession.audioMix = exportAudioMix;