AVAsset tracks is empty - ios

Question

Essentially I am looking to concatenate AVAsset files. I've got a rough idea of what to do but I'm struggling with loading the audio files.
I can play the files with an AVAudioPlayer, I can see them in the directory via my terminal, but when I attempt to load them with AVAssetURL it always returns an empty array for tracks.
The URL I am using:
NSURL *firstAudioFileLocation = [NSURL fileURLWithPath:[NSString stringWithFormat:#"%#%#", workingDirectory , #"/temp.pcm"]];
Which results in:
file:///Users/evolve/Library/Developer/CoreSimulator/Devices/8BF465E8-321C-47E6-BF2E-049C5E900F3C/data/Containers/Data/Application/4A2D29B2-E5B4-4D07-AE6B-1DD15F5E59A3/Documents/temp.pcm
The asset being loaded:
AVAsset *test = [AVURLAsset URLAssetWithURL:firstAudioFileLocation options:nil];
However when calling this:
NSLog(#" total tracks %#", test.tracks);
My output is always total tracks ().
My subsequent calls to add them to my AVMutableCompositionTrack end up crashing the app as the AVAsset seems to not have loaded correctly.
I have played with other variations for loading the asset including:
NSURL *alternativeLocation = [[NSBundle mainBundle] URLForResource:#"temp" withExtension:#"pcm"];
As well as trying to load AVAsset with the options from the documentation:
NSDictionary *assetOptions = #{AVURLAssetPreferPreciseDurationAndTimingKey: #YES};
How do I load the tracks from a local resource, recently created by the AVAudioRecorder?
EDIT
I had a poke around and found I can record and load a .CAF file extension.
Seems .PCM is unsupported for AVAsset, this page also was of great help. https://developer.apple.com/documentation/avfoundation/avfiletype

Answer 1

An AVAsset load is not instantaneous. You need to wait for the data to be available. Example:
AVAsset *test = [AVURLAsset URLAssetWithURL:firstAudioFileLocation options:nil];
[test loadValuesAsynchronouslyForKeys:#[#"playable",#"tracks"] completionHandler:^{
// Now tracks is available
NSLog(#" total tracks %#", test.tracks);
}];
A more detailed example can be found in the documentation.