Building a Playlist with AV Foundation

Slides from my talk at iOSDevCampDC 2013 about building playlists with AV Foundation.

Transcript

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

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

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3. Why just music?
   AV Foundation
   Audio-only
   Classes
   

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4. View Slide

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6. UIKit
   Core Audio Core Media Core Animation
   Media Player
   AV Foundation
   

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7. MPMusicPlayerController
   

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8. 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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10. UIKit
    Core Audio Core Media Core Animation
    Media Player
    AV Foundation
    

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11. Players
    

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12. AVPlayer
    AVQueuePlayer
    

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13. AVURLAsset *asset =
    [AVURLAsset URLAssetWithURL:
    options:nil];
    !
    !
    AVPlayerItem *playerItem =
    [[AVPlayerItem alloc] initWithAsset:asset];
    !
    !
    AVPlayer *audioPlayer =
    [[AVPlayer alloc] initWithPlayerItem:playerItem];
    !
    !
    [audioPlayer play];
    

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

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15. Assets
    

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

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17. Time
    

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18. CMTime fiveSeconds = CMTimeMake(5, 1);
    CMTime halfSecond = CMTimeMake(1, 2);
    CMTime thirtyFPS = CMTimeMake(1, 30);
    CMTimeAdd(, )
    !
    CMTimeSubtract(, subtrahend#>)
    !
    CMTimeShow()
    

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19. CMTimeRange range = CMTimeRangeMake(CMTimeMake(5,
    1), CMTimeMake(5, 1));
    !
    CMTimeRangeMake(, duration#>)
    !
    CMTimeRangeContainsTime(,
    )
    !
    CMTimeRangeShow()
    

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20. Demo
    

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22. Compositions and
    AudioMix
    

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23. AVComposition
    

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24. AVCompositionTrack
    

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25. AVCompositionTrack
    AVCompositionTrack
    

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26. AVCompositionTrack (Video)
    AVCompositionTrack (Audio)
    

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

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

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

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30. A composition is an
    asset.
    

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

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32. 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];
    

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33. Demo
    

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35. Questions?
    You can even ask why so much Hasselhoff?
    

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

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