Question

long time reader, first time asker…

I am making a music app which uses AVAssetReader to read mp3 data from the itunes library. I need precise timing, so when I create an AVURLAsset, I use the “AVURLAssetPreferPreciseDurationAndTimingKey” to extract timing data. This has some overhead (and I have no problems when I don’t use it, but I need it!)

Every thing works fine on iphone(4) and ipad(1). I would like it to work on my ipod touch (2nd gen). But it doesn’t: if the sound file is too long (> ~7 minutes) then the AVAssetReader cannot start reading and throws an error ( AVFoundationErrorDomain error -11800. )

It appears that I am hitting a wall in terms of the scanter resources of the ipod touch. Any ideas what is happening, or how to manage the overhead of creating the AVURLAsset so that it can handle long files?
(I tried running this with the performance tools, and I don’t see a major spike in memory).

Thanks, Dan

Answer 1

Maybe you’re starting to read too son? As far as I understand, for mp3 it will need to go trough the entire file in order to to enable precise timing. So, try delaying the reading.
You can also try registering as an observer for some of the AVAsset properties. iOS 4.3 has ‘readable’ property. I’ve never tried it, but my guess would be it’s initially set to NO and as soon as AVAsset has finished loading it gets set to YES.

EDIT:
Actually, just looked into the docs. You’re supposed to use AVAsynchronousKeyValueLoading protocol for that and Apple provides an example

NSURL *url = <#A URL that identifies an audiovisual asset such as a movie file#>;
AVURLAsset *anAsset = [[AVURLAsset alloc] initWithURL:url options:nil];
NSArray *keys = [NSArray arrayWithObject:@"duration"];

[asset loadValuesAsynchronouslyForKeys:keys completionHandler:^() {

    NSError *error = nil;
    AVKeyValueStatus durationStatus = [asset statusOfValueForKey:@"duration" error:&error];
    switch (durationStatus) {
        case AVKeyValueStatusLoaded:
            [self updateUserInterfaceForDuration];
            break;
        case AVKeyValueStatusFailed:
            [self reportError:error forAsset:asset];
            break;
        case AVKeyValueStatusCancelled:
            // Do whatever is appropriate for cancelation.
            break;
   }
}];

If ‘duration’ won’t help try ‘readable’ (but like I mentioned before ‘readable’ requires 4.3). Maybe this will solve your issue.