How do you force audio to come out of the iPhone speaker when a headset is attached?

I'm trying to add a loudspeaker feature to one of开发者_运维问答 my iPhone apps. I already created the recording functionality, but when I play the recorded audio it only plays to the phone headset.

What I need is the recorded file to be played on the loudspeaker, even if there is a headset attached. How could I reroute the audio to do this?

You need to override the default audio properties using AudioSessionSetProperty. Look at something like this to force all audio to go to the speaker (note that this will even happen if headphones are plugged in).

OSStatus err = 0;
UInt32 audioRouteOverride = kAudioSessionOverrideAudioRoute_Speaker;
err = AudioSessionSetProperty(kAudioSessionProperty_OverrideAudioRoute,sizeof(audioRouteOverride),&audioRouteOverride);

To detect the headphones, try this (this is literally copy/paste code off of another SO post, so caveat emptor, but it works for me):

/**
 * Tells us if the headset is plugged in
 */
- (BOOL) headsetIsPluggedIn
{
  BOOL returnVal = NO;

  UInt32 routeSize = sizeof(CFStringRef);
  CFStringRef route = NULL;
  OSStatus error = AudioSessionGetProperty(kAudioSessionProperty_AudioRoute, &routeSize, &route);
  if (!error && (route != NULL) && ([(NSString*)route rangeOfString:@"Head"].location != NSNotFound))
  {
    CFRelease(route);
    returnVal = YES;
  }
  return returnVal;
}

EDIT: There is a bit of a discussion in the comments about whether the CFRelease is appropriate or not. Any hardcore Core Foundation experts care to weigh in?