Subdividing camera image into smaller regions and time multiplexing them so that I can read more than 4 markers simultaneously. Works badly. SO: http://stackoverflow.com/questions/19431661/avcapturemetadataoutput-detect-more-than-four-4-qr-codes

reg.m

- (id)init
{
    ...
    static const float w = 1. / subdivisionColumns, h = 1. / subdivisionRows;
    int i = 0;
    for(int y = 0; y < subdivisionRows; y++) {
        for(int x = 0; x < subdivisionColumns; x++, i++) {
            _regions[i] = CGRectMake(x*w, y*h, w*1.5, h*1.5);

        }
    }
    [NSTimer scheduledTimerWithTimeInterval:0.2 target:self selector:@selector(changeRectOfInterest) userInfo:nil repeats:YES];

    return self;
}

- (void)changeRectOfInterest
{
    _currentRegionIndex = (_currentRegionIndex + 1) % (subdivisionRows*subdivisionColumns);
    _overlay.drawThis = _metadataOutput.rectOfInterest = _regions[_currentRegionIndex];
    [_overlay setNeedsDisplay];
}

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputMetadataObjects:(NSArray *)metadataObjects fromConnection:(AVCaptureConnection *)connection
{
    _objectsInRegion[@(_currentRegionIndex)] = metadataObjects;
    NSMutableArray *allObjects = [NSMutableArray new];
    NSMutableSet *allIdentifiers = [NSMutableSet new];
    for(NSArray *regionObjects in _objectsInRegion.allValues) {
        for(id object in regionObjects) {
            if(![allIdentifiers containsObject:[object stringValue]]) {
                [allObjects addObject:object];
                [allIdentifiers addObject:[object stringValue]];
            }
        }
    }