Question

Xcode for iOS

The issue that I’m having is in the playback of an AVMutableComposition. I’m creating the composition then adding AVURLAssets to it inside a for loop. I’m adding everything as I would similarly add an object to a mutable array and then attempting to play it back afterwards, but playback isn’t occuring. Here is my code:

AVMutableComposition *composition = [AVMutableComposition composition];

int count;

count = array.count;

for (int y=0;y<count;y++){    

        NSURL *url;

            url = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%@.mp3", [[NSBundle mainBundle] resourcePath],[array objectAtIndex:y]]];





        NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];

        AVURLAsset *sourceAsset = [[AVURLAsset alloc] initWithURL:url options:options];

        //calculate times
        NSNumber *time = [soundArray1 objectAtIndex:1];

        double timenow = [time doubleValue];
        double insertTime = (240*y);

        CMTime douTime = CMTimeMake(240, timenow);
        CMTime staTime = CMTimeMake(0, 1);
        CMTimeRange editRange = CMTimeRangeMake(staTime,douTime);

        CMTime insTime = CMTimeMake(insertTime, timenow);


        NSError *editError;


        [composition insertTimeRange:editRange ofAsset:sourceAsset atTime:insTime error:&editError];

    }


AVPlayer* mp = [AVPlayer playerWithPlayerItem:[AVPlayerItem playerItemWithAsset:composition]];


[mp play];

I’d assume that I am getting it completely wrong, but I then added this inside the loop instead of after, inside an if and opening a NSRunLoop to check (a little bad, but it was just to test!):

    AVMutableComposition *composition = [AVMutableComposition composition];

int count;

count = array.count;

for (int y=0;y<count;y++){    

        NSURL *url;

            url = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%@.mp3", [[NSBundle mainBundle] resourcePath],[array objectAtIndex:y]]];





        NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];

        AVURLAsset *sourceAsset = [[AVURLAsset alloc] initWithURL:url options:options];

        //calculate times
        NSNumber *time = [soundArray1 objectAtIndex:1];

        double timenow = [time doubleValue];
        double insertTime = (240*y);

        CMTime douTime = CMTimeMake(240, timenow);
        CMTime staTime = CMTimeMake(0, 1);
        CMTimeRange editRange = CMTimeRangeMake(staTime,douTime);

        CMTime insTime = CMTimeMake(insertTime, timenow);


        NSError *editError;


        [composition insertTimeRange:editRange ofAsset:sourceAsset atTime:insTime error:&editError];



    if(y==3){

    AVPlayer* mp = [AVPlayer playerWithPlayerItem:[AVPlayerItem playerItemWithAsset:composition]];


    [mp play];


    [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:20]];

        }
    }

Here, I just gave my array 4 elements and made it play the composition on the 4th run-through. It worked and played my 4 audio files in perfect order.

What do I need to do to make my composition play after this loop rather than in it? Am I mis-using the system?

EDIT: by sticking my open RunLoop code on the end, it plays. Should I be doing it this way, or is there a better way to do this?

Answer 1

So I was going about this the wrong way. I needed to create an AVMutableCompositionTrack for each element and add that to my composition

       NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES]
                                                            forKey:AVURLAssetPreferPreciseDurationAndTimingKey];

        AVURLAsset *sourceAsset = [[AVURLAsset alloc] initWithURL:url options:options];

        //calculate times
        NSNumber *time = [soundArray1 objectAtIndex:1];

        double timenow = [time doubleValue];

        double insertTime = (240*y);

                    AVMutableCompositionTrack *track =
        [composition addMutableTrackWithMediaType:AVMediaTypeAudio
                                 preferredTrackID:kCMPersistentTrackID_Invalid];

        //insert the audio track from the asset into the track added to the mutable composition
        AVAssetTrack *myTrack = [[sourceAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
        CMTimeRange myTrackRange = myTrack.timeRange;
        NSError *error = nil;
        [track insertTimeRange:myTrackRange
                                      ofTrack:myTrack
                                       atTime:CMTimeMake(insertTime, timenow) 
                                        error:&error];

        [sourceAsset release];

followed by

AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:composition];
self.player = [[AVPlayer alloc] initWithPlayerItem:playerItem];


        [self.player play];

with player declared as a property in the interface section

@interface SecondViewController ()



@property (nonatomic, assign) AVPlayer *player;



@end