Hi sentio,

Since you didn't say, I'll assume you are on QCAR SDK 1.5.8 on iOS writing native iOS apps.

To set simultaneous tracking you need to add a hint in EAGLView.mm:

// called after QCAR is initialised but before the camera starts
- (void) postInitQCAR
{
    // These two calls to setHint tell QCAR to split work over multiple
    // frames.  Depending on your requirements you can opt to omit these.
    QCAR::setHint(QCAR::HINT_IMAGE_TARGET_MULTI_FRAME_ENABLED, 1);
    QCAR::setHint(QCAR::HINT_IMAGE_TARGET_MILLISECONDS_PER_MULTI_FRAME, 25);
    
    // Here we could also make a QCAR::setHint call to set the maximum
    // number of simultaneous targets                
    // QCAR::setHint(QCAR::HINT_MAX_SIMULTANEOUS_IMAGE_TARGETS, 2);
}

Find the above function and uncomment the last line - you can increase the number of simultaneous targets but be aware of performance degradation if you have complex augmentations.