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copied!<p>Yes it is possible, here is a snippet of code that is used to add audio to an existing composition, i grabbed this from apples sample code, you should probably view the whole project, youll find it very useful, the project is AVEditDemo and you can find it in the WWDC 2010 material that they posted here developer.apple.com/videos/wwdc/2010. Hope that helps</p> <pre><code> - (void)addCommentaryTrackToComposition:(AVMutableComposition *)composition withAudioMix:(AVMutableAudioMix *)audioMix { NSInteger i; NSArray *tracksToDuck = [composition tracksWithMediaType:AVMediaTypeAudio]; // before we add the commentary // Clip commentary duration to composition duration. CMTimeRange commentaryTimeRange = CMTimeRangeMake(self.commentaryStartTime, self.commentary.duration); if (CMTIME_COMPARE_INLINE(CMTimeRangeGetEnd(commentaryTimeRange), >, [composition duration])) commentaryTimeRange.duration = CMTimeSubtract([composition duration], commentaryTimeRange.start); // Add the commentary track. AVMutableCompositionTrack *compositionCommentaryTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid]; [compositionCommentaryTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, commentaryTimeRange.duration) ofTrack:[[self.commentary tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:commentaryTimeRange.start error:nil]; NSMutableArray *trackMixArray = [NSMutableArray array]; CMTime rampDuration = CMTimeMake(1, 2); // half-second ramps for (i = 0; i < [tracksToDuck count]; i++) { AVMutableAudioMixInputParameters *trackMix = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:[tracksToDuck objectAtIndex:i]]; [trackMix setVolumeRampFromStartVolume:1.0 toEndVolume:0.2 timeRange:CMTimeRangeMake(CMTimeSubtract(commentaryTimeRange.start, rampDuration), rampDuration)]; [trackMix setVolumeRampFromStartVolume:0.2 toEndVolume:1.0 timeRange:CMTimeRangeMake(CMTimeRangeGetEnd(commentaryTimeRange), rampDuration)]; [trackMixArray addObject:trackMix]; } audioMix.inputParameters = trackMixArray; </code></pre> <p>}</p>

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