AVSimpleEditorOSX/AVSEAddMusicCommand.m

/*
     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