AVMutableAudioMix and AVAssetExportSession (Help!!!)

Question

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

Trim works perfect! But fade in/out doesn't :(((

    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;
...

    myDeleteFile(filePath);
    exportSession.outputURL = [NSURL fileURLWithPath:filePath];


    [exportSession exportAsynchronouslyWithCompletionHandler:^{

        if (exportSession.status == AVAssetExportSessionStatusCompleted) {
            NSLog(@"export session completed");
            //
            //return YES;
        } else {
            NSLog(@"export session error");
            //return NO;
        }

        [exportSession release];
    }];