Core Audio in iOS 6 (CocoaConf Portland, Oct. '12)

Core Audio in iOS 6 Chris Adamson • @invalidname CocoaConf PDX October 27, 2012Slides and sample code will be available later today

The Reviews Are In!

Legitimate copies!• Amazon (paper or Kindle)• Barnes & Noble (paper or Nook)• Apple (iBooks)• Direct from InformIT (paper, eBook [.epub + .mobi + .pdf], or Bundle) • 35% off with code COREAUDIO3174

What You’ll Learn• What Core Audio does and doesn’t do• When to use and not use it• What’s new in Core Audio for iOS 6

Simple things should be simple,complex things should be possible. –Alan Kay

AV Foundation, Media Player Simple things should be simple, complex things should be possible. –Alan Kay

AV Foundation, Media Player Simple things should be simple, complex things should be possible. –Alan Kay Core Audio

Core Audio• Low-level C framework for processing audio • Capture, play-out, real-time or off-line processing• The “complex things should be possible” part of audio on OS X and iOS

Chris’ CA Taxonomy• Engines: process streams of audio • Capture, play-out, mixing, effects processing• Helpers: deal with formats, encodings, etc. • File I/O, stream I/O, format conversion, iOS “session” management

Helpers: Audio File• Read from / write to multiple audio ﬁle types (.aiff, .wav, .caf, .m4a, .mp3) in a content-agnostic way• Get metadata (data format, duration, iTunes/ID3 info)

Helpers: Audio File Stream• Read audio from non-random-access source like a network stream• Discover encoding and encapsulation on the ﬂy, then deliver audio packets to client application

Helpers: Converters• Convert buffers of audio to and from different encodings• One side must be in an uncompressed format (i.e., Linear PCM)

Helpers: ExtAudioFile• Combine file I/O and format conversion• Read a compressed file into PCM buffers• Write PCM buffers into a compressed file

Helpers: Audio Session• iOS-only API to negotiate use of audio resources with the rest of the system• Deetermine whether your app mixes with other apps’ audio, honors ring/silent switch, can play in background, etc.• Gets notiﬁed of audio interruptions• See also AVAudioSession

Engines: Audio Units• Low-latency (~10ms) processing of capture/play-out audio data• Effects, mixing, etc.• Connect units manually or via an AUGraph• Much more on this topic momentarily…

Engines: Audio Queue• Convenience API for recording or play-out, built atop audio units• Rather than processing on-demand and on Core Audio’s thread, your callback provides or receives buffers of audio (at whatever size is convenient to you)• Higher latency, naturally• Supports compressed formats (MP3, AAC)

Engines: Open AL• API for 3D spatialized audio, implemented atop audio units• Set a source’s properties (x/y/z coordinates, orientation, audio buffer, etc.), OpenAL renders what it sounds like to the listener from that location

Engines and Helpers• Audio Units • Audio File• Audio Queue • Audio File Stream• Open AL • Audio Converter • ExtAudioFile • Audio Session

Audio Units

Audio Unit AUSomething

Types of Audio Units• Output (which also do input)• Generator• Converter• Effect• Mixer• Music

Pull Model AUSomething

Pull Model AUSomething AudioUnitRender()

Pull ModelAUSomethingElse AUSomething

Buses (aka, Elements) AUSomethingElse AUSomething AUSomethingElse

AUGraphAUSomethingElse AUSomethingAUSomethingElse

Render CallbacksOSStatus converterInputRenderCallback (void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList * ioData) { CCFWebRadioPlayer *player = (__bridge CCFWebRadioPlayer*) inRefCon; // read from buffer ioData->mBuffers[0].mData = player.preRenderData; return noErr;} AUSomething AUSomethingElse

AURemoteIO• Output unit used for play-out, capture• A Core Audio thread repeatedly and automatically calls AudioUnitRender()• Must set EnableIO property to explicitly enable capture and/or play-out • Capture requires setting appropriate AudioSession category

Create AURemoteIOCheckError(NewAUGraph(&_auGraph),! ! "couldnt create au graph");!CheckError(AUGraphOpen(_auGraph),! ! "couldnt open au graph");!AudioComponentDescription componentDesc;componentDesc.componentType = kAudioUnitType_Output;componentDesc.componentSubType = kAudioUnitSubType_RemoteIO;componentDesc.componentManufacturer = kAudioUnitManufacturer_Apple;!AUNode remoteIONode;CheckError(AUGraphAddNode(_auGraph,! ! ! ! ! ! &componentDesc,! ! ! ! ! ! &remoteIONode),! ! "couldnt add remote io node");

Getting an AudioUnit from AUNode! CheckError(AUGraphNodeInfo(self.auGraph,! ! ! ! ! ! ! remoteIONode,! ! ! ! ! ! ! NULL,! ! ! ! ! ! ! &_remoteIOUnit),! ! ! "couldnt get remote io unit from node");

AURemoteIO Buses AURemoteIO

AURemoteIO Buses AURemoteIO bus 0 to output H/W

AURemoteIO Buses AURemoteIO bus 0 bus 0from app to output H/W

AURemoteIO Buses bus 1from input H/W AURemoteIO bus 0 bus 0 from app to output H/W

AURemoteIO Buses bus 1 bus 1from input H/W to app AURemoteIO bus 0 bus 0 from app to output H/W

EnableIO! UInt32 oneFlag = 1;! UInt32 busZero = 0;! CheckError(AudioUnitSetProperty(self.remoteIOUnit,! ! ! ! ! ! ! ! ! kAudioOutputUnitProperty_EnableIO,! ! ! ! ! ! ! ! ! kAudioUnitScope_Output,! ! ! ! ! ! ! ! ! busZero,! ! ! ! ! ! ! ! ! &oneFlag,! ! ! ! ! ! ! ! ! sizeof(oneFlag)),! ! ! "couldnt enable remote io output");! UInt32 busOne = 1;! CheckError(AudioUnitSetProperty(self.remoteIOUnit,! ! ! ! ! ! ! ! ! kAudioOutputUnitProperty_EnableIO,! ! ! ! ! ! ! ! ! kAudioUnitScope_Input,! ! ! ! ! ! ! ! ! busOne,! ! ! ! ! ! ! ! ! &oneFlag,! ! ! ! ! ! ! ! ! sizeof(oneFlag)),! ! ! "couldnt enable remote io input");

Pass Through bus 1from input H/W AURemoteIO bus 0 to output H/W

Connect In to Out! UInt32 busZero = 0;! UInt32 busOne = 1;! CheckError(AUGraphConnectNodeInput(self.auGraph,! ! ! ! ! ! ! ! ! remoteIONode,! ! ! ! ! ! ! ! ! busOne,! ! ! ! ! ! ! ! ! remoteIONode,! ! ! ! ! ! ! ! ! busZero),! ! ! "couldnt connect remote io bus 1 to 0");

Pass-Through with Effect AUEffect bus 1 from input H/W AURemoteIO bus 0 to output H/W

Demo: Delay Effect New in iOS 6!

Creating the AUDelay! componentDesc.componentType = kAudioUnitType_Effect;! componentDesc.componentSubType = kAudioUnitSubType_Delay;! componentDesc.componentManufacturer = kAudioUnitManufacturer_Apple;!! AUNode effectNode;! CheckError(AUGraphAddNode(self.auGraph,! ! ! ! ! ! ! &componentDesc,! ! ! ! ! ! ! &effectNode),! ! ! "couldnt create effect node");! AudioUnit effectUnit;! CheckError(AUGraphNodeInfo(self.auGraph,! ! ! ! ! ! ! effectNode,! ! ! ! ! ! ! NULL,! ! ! ! ! ! ! &effectUnit),! ! ! "couldnt get effect unit from node");

The problem with effect units• Audio Units available since iPhone OS 2.0 prefer int formats• Effect units arrived with iOS 5 (arm7 era) and only work with ﬂoat format• Have to set the AUEffect unit’s format on AURemoteIO

Setting formats! AudioStreamBasicDescription effectDataFormat;! UInt32 propSize = sizeof (effectDataFormat);! CheckError(AudioUnitGetProperty(effectUnit,! ! ! ! ! ! ! ! ! kAudioUnitProperty_StreamFormat,! ! ! ! ! ! ! ! ! kAudioUnitScope_Output,! ! ! ! ! ! ! ! ! busZero,! ! ! ! ! ! ! ! ! &effectDataFormat,! ! ! ! ! ! ! ! ! &propSize),! ! ! "couldnt read effect format");! CheckError(AudioUnitSetProperty(self.remoteIOUnit,! ! ! ! ! ! ! ! ! kAudioUnitProperty_StreamFormat,! ! ! ! ! ! ! ! ! kAudioUnitScope_Output,! ! ! ! ! ! ! ! ! busOne,! ! ! ! ! ! ! ! ! &effectDataFormat,! ! ! ! ! ! ! ! ! propSize),! ! ! "couldnt set bus one output format"); Then repeat AudioUnitSetProperty() for input scope / bus 0

AUNewTimePitch• New in iOS 6!• Allows you to change pitch independent of time, or time independent of pitch• How do you use it?

AUTimePitch! AudioComponentDescription effectcd = {0};! effectcd.componentType = kAudioUnitType_FormatConverter;! effectcd.componentSubType = kAudioUnitSubType_NewTimePitch;! effectcd.componentManufacturer = kAudioUnitManufacturer_Apple;!! AUNode effectNode;! CheckError(AUGraphAddNode(self.auGraph,! ! ! ! ! ! ! &effectcd,! ! ! ! ! ! ! &effectNode),! ! ! "couldnt get effect node [time/pitch]"); Notice the type is AUFormatConverter, not AUEffect

AudioUnitParameters.h // Parameters for AUNewTimePitch enum { ! ! // Global, rate, 1/32 -> 32.0, 1.0 ! kNewTimePitchParam_Rate! ! ! ! ! ! = ! 0, ! ! // Global, Cents, -2400 -> 2400, 1.0 ! kNewTimePitchParam_Pitch! ! ! ! ! ! = 1, ! ! // Global, generic, 3.0 -> 32.0, 8.0 ! kNewTimePitchParam_Overlap! ! ! ! ! ! = 4, ! ! // Global, Boolean, 0->1, 1 ! kNewTimePitchParam_EnablePeakLocking! ! ! = 6 };This is the entire documentation for the AUNewTimePitch parameters

AUNewTimePitch parameters• Rate: kNewTimePitchParam_Rate takes a Float32 rate from 1/32 speed to 32x speed. • Use powers of 2: 1/32, 1/16, …, 2, 4, 8…• Pitch: kNewTimePitchParam_Pitch takes a Float32 representing cents, meaning 1/100 of a musical semitone

Pitch shifting• Pitch can vary, time does not• Suitable for real-time sources, such as audio capture

Demo: Pitch Shift New in iOS 6!

Rate shifting• Rate can vary, pitch does not • Think of 1.5x and 2x speed modes in Podcasts app• Not suitable for real-time sources, as data will be consumed faster. Files work well. • Sources must be able to map time systems with kAudioUnitProperty_InputSamplesInOutput

Demo: Rate Shift New in iOS 6!

AUSplitter AUSomethingElseAUSplitter AUSomethingElse New in iOS 6!

AUMatrixMixerAUSomethingElse AUSomethingElseAUSomethingElse AUMatrixMixer AUSomethingElseAUSomethingElse New in iOS 6!

Audio Queues(and the APIs that help them)

AudioQueue• Easier than AURemoteIO - provide data when you want to, less time pressure, can accept or provide compressed formats (MP3, AAC)• Recording queue - receive buffers of captured audio in a callback• Play-out queue - enqueue buffers of audio to play, optionally reﬁll in a callback

AudioQueue 2 1 0

Common AQ scenarios• File player - Read from file and “prime” queue buffers, start queue, when called back with used buffer, refill from next part of file• Synthesis - Maintain state in your own code, write raw samples into buffers during callbacks

Web Radio• Thursday class’ third project• Use Audio File Stream Services to pick out audio data from a network stream• Enqueue these packets as new AQ buffers• Dispose used buffers in callback

Parsing web radio

Parsing web radioNSURLConnection deliversNSData buffers, containing audioand framing info. We pass it to NSData NSDataAudio File Services. Packets Packets Packets Packets Packets

Parsing web radioNSURLConnection deliversNSData buffers, containing audioand framing info. We pass it to NSData NSDataAudio File Services. Packets Packets Packets Packets Packets Packets PacketsAudio File Services calls us backwith parsed packets of audio data. Packets Packets Packets

Parsing web radioNSURLConnection deliversNSData buffers, containing audioand framing info. We pass it to NSData NSDataAudio File Services. Packets Packets Packets Packets Packets Packets PacketsAudio File Services calls us backwith parsed packets of audio data. Packets Packets PacketsWe create an AudioQueueBuffer Packets Packetswith those packets and enqueue it Packets 2 Packets 1 0for play-out. Packets Packets

A complex thing!• What if we want to see that data after it’s been decoded to PCM and is about to be played? • e.g., spectrum analysis, effects, visualizers• AudioQueue design is “ﬁre-and-forget”

AudioQueue Tap!http://www.last.fm/music/Spinal+Tap

AudioQueueProcessingTap• Set as a property on the Audio Queue• Calls back to your function with decoded (PCM) audio data• Three types: pre- or post- effects (that the AQ performs), or siphon. First two can modify the data.• Only documentation is in AudioQueue.h

Creating an AQ Tap! ! // create the tap! ! UInt32 maxFrames = 0;! ! AudioStreamBasicDescription tapFormat = {0};! ! AudioQueueProcessingTapRef tapRef;! ! CheckError(AudioQueueProcessingTapNew(audioQueue,! ! ! ! ! ! ! ! ! ! ! tapProc,! ! ! ! ! ! ! ! ! ! ! (__bridge void *)(player),! ! ! ! ! ! ! ! ! ! ! kAudioQueueProcessingTap_PreEffects,! ! ! ! ! ! ! ! ! ! ! &maxFrames,! ! ! ! ! ! ! ! ! ! ! &tapFormat,! ! ! ! ! ! ! ! ! ! ! &tapRef),! ! ! ! "couldnt create AQ tap"); Notice that you receive maxFrames and tapFormat. These do not appear to be settable.

AQ Tap Procvoid tapProc (void * inClientData,! ! ! AudioQueueProcessingTapRef inAQTap,! ! ! UInt32 inNumberFrames,! ! ! AudioTimeStamp * ioTimeStamp,! ! ! UInt32 * ioFlags,! ! ! UInt32 * outNumberFrames,! ! ! AudioBufferList * ioData) {! CCFWebRadioPlayer *player = (__bridge CCFWebRadioPlayer*) inClientData;! UInt32 getSourceFlags = 0;! UInt32 getSourceFrames = 0;! AudioQueueProcessingTapGetSourceAudio(inAQTap,! ! ! ! ! ! ! ! ! ! inNumberFrames,! ! ! ! ! ! ! ! ! ! ioTimeStamp,! ! ! ! ! ! ! ! ! ! &getSourceFlags,! ! ! ! ! ! ! ! ! ! &getSourceFrames,! ! ! ! ! ! ! ! ! ! ioData); // then do something with ioData // ...

So what should we do with the audio?

So what should we do with the audio? Let’s apply our pitch-shift effect

Shouldn’t this work? AUEffect

Shouldn’t this work? AUEffect AudioUnitRender()

AudioUnitRender()• Last argument is an AudioBufferList, whose AudioBuffer members have mData pointers • If mData != NULL, audio unit does its thing with those samples • If mData == NULL, audio data pulls from whatever it’s connected to• So we just call with AudioBufferList ioData we got from tap callback, right?

Psych!• AQ tap provides data as signed ints• Effect units only work with ﬂoating point• We need to do an on-the-spot format conversion

invalidname’s convert- and-effect recipe OSStatus converterInputRenderCallback (void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList * ioData) { CCFWebRadioPlayer *player = (__bridge CCFWebRadioPlayer*) inRefCon; // read from buffer ioData->mBuffers[0].mData = player.preRenderData; return noErr; } AUConverter AUEffect AUConverter AUGenericOutputNote: red arrows are ﬂoat format, yellow arrows are int

How it works• AUGraph: AUConverter → AUEffect → AUConverter → AUGenericOutput• Top AUConverter is connected to a render callback function

The trick!• Copy mData pointer to a state variable and NULL it in ioData• Call AudioQueueRender() on output unit. The NULL makes it pull from the graph.• Top of the graph pulls on render callback, which gives it back the mData we copied off.

Yes, really This is the rest of tapProc()! // copy off the ioData so the graph can read from it // in render callback! player.preRenderData = ioData->mBuffers[0].mData;! ioData->mBuffers[0].mData = NULL;!! OSStatus renderErr = noErr;! AudioUnitRenderActionFlags actionFlags = 0;! renderErr = AudioUnitRender(player.genericOutputUnit,! ! ! ! ! ! ! ! &actionFlags,! ! ! ! ! ! ! ! player.renderTimeStamp,! ! ! ! ! ! ! ! 0,! ! ! ! ! ! ! ! inNumberFrames,! ! ! ! ! ! ! ! ioData);! NSLog (@"AudioUnitRender, renderErr = %ld",renderErr);}

Yes, really This is the render callback that supplies data to the int→ﬂoat converterOSStatus converterInputRenderCallback (void *inRefCon,! ! ! ! ! ! ! ! ! AudioUnitRenderActionFlags *ioActionFlags,! ! ! ! ! ! ! ! ! const AudioTimeStamp *inTimeStamp,! ! ! ! ! ! ! ! ! UInt32 inBusNumber,! ! ! ! ! ! ! ! ! UInt32 inNumberFrames,! ! ! ! ! ! ! ! ! AudioBufferList * ioData) {! CCFWebRadioPlayer *player = (__bridge CCFWebRadioPlayer*) inRefCon;!! // read from buffer! ioData->mBuffers[0].mData = player.preRenderData;! return noErr;}

Demo: AQ Tap +AUNewTimePitch New in iOS 6!

Other new stuff

Multi-Route• Ordinarily, one input or output is active: earpiece, speaker, headphones, dock- connected device • “Last in wins”• With AV Session “multi-route” category, you can use several at once• WWDC 2012 session 505

Utility classes moved again• C++ utilities, including the CARingBuffer • < Xcode 4.3, installed into /Developer • Xcode 4.3-4.4, optional download from developer.apple.com • ≧ Xcode 4.5, sample code project “Core Audio Utility Classes”

Takeaways• Core Audio fundamentals never change• New stuff is added as properties, typedefs, enums, etc.• Watch the SDK API diffs document to ﬁnd the new stuff• Hope you like header ﬁles and experimentation

Q&A• Slides will be posted to slideshare.net/ invalidname• Code will be linked from there and my blog• Watch CocoaConf PDX glassboard, @invalidname on Twitter/ADN, or [Time code]; blog for announcement• Thanks!

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Core Audio in iOS 6 (CocoaConf Portland, Oct. '12)

by Chris Adamson on Oct 27, 2012

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