/*

     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: 1.1

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 */

#import "AVSEAddMusicCommand.h"

@implementation AVSEAddMusicCommand

- (void)performWithAsset:(AVAsset*)asset

{

    AVAssetTrack *assetVideoTrack = nil;

    AVAssetTrack *assetAudioTrack = nil;

    // Check if the asset contains video and audio tracks

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

        assetVideoTrack = [asset tracksWithMediaType:AVMediaTypeVideo][0];

    }

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

        assetAudioTrack = [asset tracksWithMediaType:AVMediaTypeAudio][0];

    }

    NSError *error = nil;

    // Step 1

    // Extract the custom audio track to be added to the composition

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

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

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

    // Step 2

    // Create a composition with the given asset and insert audio and video tracks into it from the asset

    if (!self.mutableComposition) {

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

        // Create a new composition

        self.mutableComposition = [AVMutableComposition composition];

        // Add tracks to composition from the input video asset

        if (assetVideoTrack != nil) {

            AVMutableCompositionTrack *compositionVideoTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

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

        }

        if (assetAudioTrack != nil) {

            AVMutableCompositionTrack *compositionAudioTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

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

        }

    }

    // Step 3

    // Add custom audio track to the composition

    AVMutableCompositionTrack *customAudioTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

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

    // Step 4

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

    AVMutableAudioMixInputParameters *mixParameters = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:customAudioTrack];

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

    self.mutableAudioMix = [AVMutableAudioMix audioMix];

    self.mutableAudioMix.inputParameters = @[mixParameters];

    // Step 5

    // Notify AVSEViewController about add music operation completion

    [[NSNotificationCenter defaultCenter] postNotificationName:AVSEEditCommandCompletionNotification object:self];

}

@end