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
2. or: A crash course to AV Foundation
   with music. Josh Johnson @jnjosh | αjnjosh | jnjosh.com
3. Why just music? AV Foundation Audio-only Classes
6. UIKit Core Audio Core Media Core Animation Media Player AV Foundation
7. MPMusicPlayerController
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];
10. UIKit Core Audio Core Media Core Animation Media Player AV Foundation
11. Players
12. AVPlayer
    AVQueuePlayer
13. AVURLAsset *asset =
    [AVURLAsset URLAssetWithURL:<# hasselhoff.mp3 #>
    options:nil];
    ! ! AVPlayerItem *playerItem =
    [[AVPlayerItem alloc] initWithAsset:asset];
    ! ! AVPlayer *audioPlayer =
    [[AVPlayer alloc] initWithPlayerItem:playerItem];
    ! ! [audioPlayer play];
14. 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];
15. Assets
16. AVURLAsset *asset =
    [AVURLAsset URLAssetWithURL:song.url options:nil];
    ! ! [asset loadValuesAsynchronouslyForKeys:@[ @"tracks" ] completionHandler:^{
    ! NSArray *assetTracks = [asset tracksWithMediaType:AVMediaTypeAudio];
    // ...
    ! }];
17. Time
18. 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#>)
19. CMTimeRange range = CMTimeRangeMake(CMTimeMake(5, 1), CMTimeMake(5, 1)); ! CMTimeRangeMake(<#CMTime start#>, <#CMTime duration#>)
    ! CMTimeRangeContainsTime(<#CMTimeRange range#>, <#CMTime time#>)
    ! CMTimeRangeShow(<#CMTimeRange range#>)
20. Demo
22. Compositions and AudioMix
23. AVComposition
24. AVCompositionTrack
25. AVCompositionTrack AVCompositionTrack
26. AVCompositionTrack (Video) AVCompositionTrack (Audio)
27. AVCompositionTrackSegment seconds 50-60 of “the_hoff.mp3” AVCompositionTrackSegment seconds 0-10 of “the_hoff.mp3”
28. AVURLAsset *asset =
    [AVURLAsset URLAssetWithURL:song.url options:nil];
    ! ! [asset loadValuesAsynchronouslyForKeys:@[ @"tracks" ] completionHandler:^{
    ! NSArray *assetTracks = [asset tracksWithMediaType:AVMediaTypeAudio];
    // ...
    ! }];
29. 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];
30. A composition is an asset.
31. AVComposition *compositionAsset = [composition copy]; ! ! AVPlayerItem *playerItem = [[AVPlayerItem alloc] initWithAsset:compositionAsset];
    ! ! AVPlayer *audioPlayer = [[AVPlayer alloc] initWithPlayerItem:playerItem]; ! ! // Observe `status` for AVPlayerStatusReadyToPlay ! ! [audioPlayer play];
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];
33. Demo
35. Questions? You can even ask why so much Hasselhoff?
36. Thank you! Josh Johnson @jnjosh | αjnjosh | jnjosh.com