Building a Playlist
with AV Foundation Josh Johnson @jnjosh | αjnjosh | jnjosh.com 

or: A crash course to AV Foundation
with music. Josh Johnson @jnjosh | αjnjosh | jnjosh.com 

Why just music? AV Foundation Audio-only Classes 

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UIKit Core Audio Core Media Core Animation Media Player AV Foundation 

MPMusicPlayerController 

MPMusicPlayerController *player =
[MPMusicPlayerController applicationMusicPlayer]; ! // Access the music through the iPod Library Access API MPMediaQuery *query = [MPMediaQuery artistsQuery];
! [query addFilterPredicate:[MPMediaPropertyPredicate predicateWithValue:@"David Hasselhoff" forProperty:MPMediaItemPropertyArtist comparisonType:MPMediaPredicateComparisonEqualTo]]; [query setGroupingType:MPMediaGroupingArtist]; ! // Let the player have the query [player setQueueWithQuery:query]; ! // Listen to the musical stylings of David Hasselhoff [player play]; 

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UIKit Core Audio Core Media Core Animation Media Player AV Foundation 

Players 

AVPlayer
AVQueuePlayer 

AVURLAsset *asset =
[AVURLAsset URLAssetWithURL:<# hasselhoff.mp3 #>
options:nil];
! ! AVPlayerItem *playerItem =
[[AVPlayerItem alloc] initWithAsset:asset];
! ! AVPlayer *audioPlayer =
[[AVPlayer alloc] initWithPlayerItem:playerItem];
! ! [audioPlayer play]; 

AVURLAsset *asset =
[AVURLAsset URLAssetWithURL:<# hasselhoff.mp3 #>
options:nil];
! AVPlayerItem *item1 =
[[AVPlayerItem alloc] initWithAsset:asset];
! // setup asset2 and item2
! AVQueuePlayer *audioPlayer =
[AVQueuePlayer queuePlayerWithItems:@[ item1, item2 ]];
! ! [audioPlayer play]; 

Assets 

AVURLAsset *asset =
[AVURLAsset URLAssetWithURL:song.url options:nil];
! ! [asset loadValuesAsynchronouslyForKeys:@[ @"tracks" ] completionHandler:^{
! NSArray *assetTracks = [asset tracksWithMediaType:AVMediaTypeAudio];
// ...
! }]; 

Time 

CMTime fiveSeconds = CMTimeMake(5, 1); CMTime halfSecond = CMTimeMake(1, 2); CMTime thirtyFPS = CMTimeMake(1, 30); CMTimeAdd(<#CMTime addend1#>, <#CMTime addend2#>)
! CMTimeSubtract(<#CMTime minuend#>, <#CMTime subtrahend#>)
! CMTimeShow(<#CMTime time#>) 

CMTimeRange range = CMTimeRangeMake(CMTimeMake(5, 1), CMTimeMake(5, 1)); ! CMTimeRangeMake(<#CMTime start#>, <#CMTime duration#>)
! CMTimeRangeContainsTime(<#CMTimeRange range#>, <#CMTime time#>)
! CMTimeRangeShow(<#CMTimeRange range#>) 

Demo 

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Compositions and AudioMix 

AVComposition 

AVCompositionTrack 

AVCompositionTrack AVCompositionTrack 

AVCompositionTrack (Video) AVCompositionTrack (Audio) 

AVCompositionTrackSegment seconds 50-60 of “the_hoff.mp3” AVCompositionTrackSegment seconds 0-10 of “the_hoff.mp3” 

AVURLAsset *asset =
[AVURLAsset URLAssetWithURL:song.url options:nil];
! ! [asset loadValuesAsynchronouslyForKeys:@[ @"tracks" ] completionHandler:^{
! NSArray *assetTracks = [asset tracksWithMediaType:AVMediaTypeAudio];
// ...
! }]; 

AVMutableComposition *composition = [AVMutableComposition composition]; AVMutableCompositionTrack *track = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid]; AVAssetTrack *audioTrack = [assetTracks lastObject]; [track insertTimeRange:audioTrack.timeRange ofTrack:audioTrack atTime:<# CMTime #> error:&error]; 

A composition is an asset. 

AVComposition *compositionAsset = [composition copy]; ! ! AVPlayerItem *playerItem = [[AVPlayerItem alloc] initWithAsset:compositionAsset];
! ! AVPlayer *audioPlayer = [[AVPlayer alloc] initWithPlayerItem:playerItem]; ! ! // Observe `status` for AVPlayerStatusReadyToPlay ! ! [audioPlayer play]; 

AVMutableAudioMixInputParameters *params =
[AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:track]; ! CMTime crossfadeDuration = ...; CMTimeRange crossfadeEndRange = CMTimeRangeMake(CMTimeSubtract(CMTimeRangeGetEnd(songRange), crossfadeDuration), crossfadeDuration); ! // set the ramp [params setVolumeRampFromStartVolume:1.0 toEndVolume:0.0 timeRange:crossfadeEndRange]; [audioMixParameters addObject:params]; ! AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix]; [audioMix setInputParameters:audioMixParameters]; [playerItem setAudioMix:fadeMix]; 

Demo 

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Questions? You can even ask why so much Hasselhoff? 

Thank you! Josh Johnson @jnjosh | αjnjosh | jnjosh.com