Links for October 25th through January 23rd:
A customer recently got in touch with me with an odd problem — Talkie for iPhone was going silent on him. After a little diagnosis, it turned out the audio system was throwing up an undocumented error — -12986 — while starting up on his iPod Touch.
Some googling turned up this thread on Stack Overflow, which presented a solution for the AVAudioSession framework: It turns out, on recent SDKs (somewhere equal to or above 3.0), the audio system will refuse to start up if the session is set to a recording mode, with no input device available, spitting out this error. Alas, the error isn’t listed anywhere that I could find.
So, the way to fix it is to check whether there’s an input device available, then choose an audio category accordingly:
OSStatus status; UInt32 inputAvailable=0; UInt32 size = sizeof(inputAvailable); AudioSessionGetProperty(kAudioSessionProperty_AudioInputAvailable, &size, &inputAvailable); UInt32 sessionCategory; if ( inputAvailable ) { // Set the audio session category for simultaneous play and record sessionCategory = kAudioSessionCategory_PlayAndRecord; } else { // Just playback sessionCategory = kAudioSessionCategory_MediaPlayback; } status = AudioSessionSetProperty (kAudioSessionProperty_AudioCategory, sizeof (sessionCategory), &sessionCategory); checkStatus(status); |
It’s probably a good idea to respond when input becomes available or goes away, so add a property listener too:
void inputAvailablePropertyListener (void *inClientData, AudioSessionPropertyID inID, UInt32 inDataSize, const void *inData) { if ( inID = kAudioSessionProperty_AudioInputAvailable ) { UInt32 *inputAvailable = (UInt32*)inData; UInt32 sessionCategory; if ( *inputAvailable ) { // Set the audio session category for simultaneous play and record sessionCategory = kAudioSessionCategory_PlayAndRecord; } else { // Just playback sessionCategory = kAudioSessionCategory_MediaPlayback; } OSStatus status = AudioSessionSetProperty (kAudioSessionProperty_AudioCategory, sizeof (sessionCategory), &sessionCategory); checkStatus(status); } } |
then:
// Listen for audio input availability status = AudioSessionAddPropertyListener(kAudioSessionProperty_AudioInputAvailable, inputAvailablePropertyListener, NULL); |
Links for May 21st through June 2nd:
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Links for March 6th through March 16th:
Last Thursday I did an interview with Dan Grigsby from Mobile Orchard; the interview is now online.
Highlights from this interview include:
From UIView to OpenGL: the seven different implementations it took to finalize its unique — and Best App Ever award-nominated — UI.
From audio-queues to Remote IO: the four different architectural approaches he tried before finalizing audio subsystems.
The travails of trying to implement echo cancelation.
The business of making a living off of a $10 app
Listen to it here, or subscribe in iTunes (30 min.)
Read MoreJust in case there’s someone else that didn’t know this, when one gets an error code from one of the iPhone/OS X SDKs with no other information available, it can usually be looked up in the MacErrors.h header. Just open a terminal, type:
open -h MacErrors.h
Then do a search for your error code and you’ll hopefully find a corresponding macro name that gives some indication of what went wrong.
Failing that, if you have an inkling of where the error occurred (eg. the AudioToolbox framework), then you can often find the error defined within the framework’s headers:
That was, type in Terminal grep -r 'the error code', then drag the framework straight from XCode into the Terminal, where the path will be inserted.
Read MoreLinks for February 10th through February 27th: