/*

     File: AVSEAddMusicCommand.m

 Abstract: A subclass of AVSECommand which uses AVMutableAudioMix. This tool replaces the existing audio track of a AVMutableComposition with a custom audio track and shows the use of AVMutableAudioMixInputParameters to add volume ramps to the audio track.

  Version: 1.0

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 */

#import "AVSEAddMusicCommand.h"

@implementation AVSEAddMusicCommand

@synthesize mutableComposition;

@synthesize mutableAudioMix;

- (void)performWithAsset:(AVAsset*)asset 

{

    AVAssetTrack *videoTrack = nil;

    AVAssetTrack *audioTrack = nil;

    // Check if the asset contains video and audio tracks

    if ([[asset tracksWithMediaType:AVMediaTypeVideo] count] != 0) {

        videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

    }

    if ([[asset tracksWithMediaType:AVMediaTypeAudio] count] != 0) {

        audioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

    }

    NSError *error = nil;

    NSString *audioURL = [[NSBundle mainBundle] pathForResource:@"music" ofType:@"m4a"];

    AVAsset *audioAsset = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:audioURL] options:nil];

    AVAssetTrack *newAudioTrack = [[audioAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

    // Check whether a composition has already been created, i.e, some other tool has already been applied.

    if (!mutableComposition) { 

        // Create a new composition

        mutableComposition = [AVMutableComposition composition];

        // Add to tracks to composition from the input video asset

        if (videoTrack != nil) {

            AVMutableCompositionTrack *vTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

            [vTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:videoTrack atTime:kCMTimeZero error:&error];

        }

        if (audioTrack != nil) {

            AVMutableCompositionTrack *aTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

            [aTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:audioTrack atTime:kCMTimeZero error:&error];

        }    

    }

    // Add custom audio track to the composition

    AVMutableCompositionTrack *aTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

    [aTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [mutableComposition duration]) ofTrack:newAudioTrack atTime:kCMTimeZero error:&error];

    // Mix parameters sets a volume ramp for the audio track to be mixed with the existing audio track for the duration of the composition

    AVMutableAudioMixInputParameters *mixParameters = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:aTrack];

    [mixParameters setVolumeRampFromStartVolume:1 toEndVolume:0 timeRange:CMTimeRangeMake(kCMTimeZero, mutableComposition.duration)];

    mutableAudioMix = [AVMutableAudioMix audioMix];

    mutableAudioMix.inputParameters = [NSArray arrayWithObject:mixParameters];

    // Notify AVSEDocument class to reload the player view with the changes

    [[NSNotificationCenter defaultCenter] 

     postNotificationName:AVSEReloadNotification 

     object:self];

}

@end