Core Audio in iOS 6 (CocoaConf San Jose, April 2013)
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Transcript of Core Audio in iOS 6 (CocoaConf San Jose, April 2013)
Core Audio in iOS 6Chris Adamson • @invalidname
CocoaConf San JoseApril 20, 2013
Sides and code available on my blog:http://www.subfurther.com/blog
Monday, April 29, 13
Plug!
Monday, April 29, 13
The Reviews Are In!
Monday, April 29, 13
The Reviews Are In!
Monday, April 29, 13
The Reviews Are In!
Monday, April 29, 13
The Reviews Are In!
Monday, April 29, 13
Legitimate copies!
• Amazon (paper or Kindle)
• Barnes & Noble (paper or Nook)
• Apple (iBooks)
• Direct from InformIT (paper, eBook [.epub + .mobi + .pdf], or Bundle)
Monday, April 29, 13
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
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Simple things should be simple,complex things should be possible.
–Alan Kay
Monday, April 29, 13
Simple things should be simple,complex things should be possible.
–Alan Kay
AV Foundation, Media Player
Monday, April 29, 13
Simple things should be simple,complex things should be possible.
–Alan Kay
AV Foundation, Media Player
Core Audio
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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
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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
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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)
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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
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Helpers: Converters
• Convert buffers of audio to and from different encodings
• One side must be in an uncompressed format (i.e., Linear PCM)
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Helpers: ExtAudioFile
• Combine file I/O and format conversion
• Read a compressed file into PCM buffers
• Write PCM buffers into a compressed file
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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
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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…
Monday, April 29, 13
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)
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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
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Engines and Helpers• Audio Units
• Audio Queue
• Open AL
• Audio File
• Audio File Stream
• Audio Converter
• ExtAudioFile
• Audio Session
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Audio Units
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Audio Unit
AUSomething
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Types of Audio Units
• Output (which also do input)
• Generator
• Converter
• Effect
• Mixer
• Music
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Pull Model
AUSomething
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Pull Model
AUSomething
AudioUnitRender()
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Pull Model
AUSomethingAUSomethingElse
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Buses (aka, Elements)
AUSomething
AUSomethingElse
AUSomethingElse
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AUGraph
AUSomething
AUSomethingElse
AUSomethingElse
Monday, April 29, 13
Render Callbacks
AUSomething
AUSomethingElse
OSStatus converterInputRenderCallback (void *inRefCon,AudioUnitRenderActionFlags *ioActionFlags,const AudioTimeStamp *inTimeStamp,UInt32 inBusNumber,UInt32 inNumberFrames,AudioBufferList * ioData) {
CCFWebRadioPlayer *player = (__bridge CCFWebRadioPlayer*) inRefCon;
// read from bufferioData->mBuffers[0].mData = player.preRenderData;
return noErr;}
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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
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Create AURemoteIOCheckError(NewAUGraph(&_auGraph), ! ! "couldn't create au graph"); !CheckError(AUGraphOpen(_auGraph), ! ! "couldn't open au graph"); !AudioComponentDescription componentDesc;componentDesc.componentType = kAudioUnitType_Output;componentDesc.componentSubType = kAudioUnitSubType_RemoteIO;componentDesc.componentManufacturer =
kAudioUnitManufacturer_Apple; !AUNode remoteIONode;CheckError(AUGraphAddNode(_auGraph, ! ! ! ! ! ! &componentDesc, ! ! ! ! ! ! &remoteIONode), ! ! "couldn't add remote io node");
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Getting an AudioUnit from AUNode
! CheckError(AUGraphNodeInfo(self.auGraph, ! ! ! ! ! ! ! remoteIONode, ! ! ! ! ! ! ! NULL, ! ! ! ! ! ! ! &_remoteIOUnit), ! ! ! "couldn't get remote io unit from node");
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AURemoteIO Buses
AURemoteIO
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AURemoteIO Buses
AURemoteIObus 0
to output H/W
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AURemoteIO Buses
AURemoteIObus 0
to output H/Wbus 0
from app
Monday, April 29, 13
AURemoteIO Buses
AURemoteIObus 0
to output H/W
bus 1from input H/W
bus 0from app
Monday, April 29, 13
AURemoteIO Buses
AURemoteIObus 0
to output H/W
bus 1from input H/W
bus 1to app
bus 0from app
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EnableIO ! UInt32 oneFlag = 1; ! UInt32 busZero = 0; ! CheckError(AudioUnitSetProperty(self.remoteIOUnit, ! ! ! ! ! ! ! ! ! kAudioOutputUnitProperty_EnableIO, ! ! ! ! ! ! ! ! ! kAudioUnitScope_Output, ! ! ! ! ! ! ! ! ! busZero, ! ! ! ! ! ! ! ! ! &oneFlag, ! ! ! ! ! ! ! ! ! sizeof(oneFlag)), ! ! ! "couldn't enable remote io output"); ! UInt32 busOne = 1; ! CheckError(AudioUnitSetProperty(self.remoteIOUnit, ! ! ! ! ! ! ! ! ! kAudioOutputUnitProperty_EnableIO, ! ! ! ! ! ! ! ! ! kAudioUnitScope_Input, ! ! ! ! ! ! ! ! ! busOne, ! ! ! ! ! ! ! ! ! &oneFlag, ! ! ! ! ! ! ! ! ! sizeof(oneFlag)), ! ! ! "couldn't enable remote io input");
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Pass Through
AURemoteIO
bus 1from input H/W
bus 0to output H/W
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Connect In to Out
! UInt32 busZero = 0; ! UInt32 busOne = 1; ! CheckError(AUGraphConnectNodeInput(self.auGraph, ! ! ! ! ! ! ! ! ! remoteIONode, ! ! ! ! ! ! ! ! ! busOne, ! ! ! ! ! ! ! ! ! remoteIONode, ! ! ! ! ! ! ! ! ! busZero), ! ! ! "couldn't connect remote io bus 1 to 0");
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Pass-Through with Effect
bus 0to output H/W
AURemoteIO
AUEffect
bus 1from input H/W
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Demo: Delay EffectNew in iOS 6!
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Creating the AUDelay ! componentDesc.componentType = kAudioUnitType_Effect; ! componentDesc.componentSubType = kAudioUnitSubType_Delay; ! componentDesc.componentManufacturer =
kAudioUnitManufacturer_Apple; ! ! AUNode effectNode; ! CheckError(AUGraphAddNode(self.auGraph, ! ! ! ! ! ! ! &componentDesc, ! ! ! ! ! ! ! &effectNode), ! ! ! "couldn't create effect node"); ! AudioUnit effectUnit; ! CheckError(AUGraphNodeInfo(self.auGraph, ! ! ! ! ! ! ! effectNode, ! ! ! ! ! ! ! NULL, ! ! ! ! ! ! ! &effectUnit), ! ! ! "couldn't get effect unit from node");
Monday, April 29, 13
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
Monday, April 29, 13
Setting formats ! AudioStreamBasicDescription effectDataFormat; ! UInt32 propSize = sizeof (effectDataFormat); ! CheckError(AudioUnitGetProperty(effectUnit, ! ! ! ! ! ! ! ! ! kAudioUnitProperty_StreamFormat, ! ! ! ! ! ! ! ! ! kAudioUnitScope_Output, ! ! ! ! ! ! ! ! ! busZero, ! ! ! ! ! ! ! ! ! &effectDataFormat, ! ! ! ! ! ! ! ! ! &propSize), ! ! ! "couldn't read effect format"); ! CheckError(AudioUnitSetProperty(self.remoteIOUnit, ! ! ! ! ! ! ! ! ! kAudioUnitProperty_StreamFormat, ! ! ! ! ! ! ! ! ! kAudioUnitScope_Output, ! ! ! ! ! ! ! ! ! busOne, ! ! ! ! ! ! ! ! ! &effectDataFormat, ! ! ! ! ! ! ! ! ! propSize), ! ! ! "couldn't set bus one output format");
Then repeat AudioUnitSetProperty() for input scope / bus 0
Monday, April 29, 13
AUNewTimePitch
• New in iOS 6!
• Allows you to change pitch independent of time, or time independent of pitch
• How do you use it?
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AUTimePitch
! AudioComponentDescription effectcd = {0}; ! effectcd.componentType = kAudioUnitType_FormatConverter; ! effectcd.componentSubType = kAudioUnitSubType_NewTimePitch; ! effectcd.componentManufacturer = kAudioUnitManufacturer_Apple; ! ! AUNode effectNode; ! CheckError(AUGraphAddNode(self.auGraph, ! ! ! ! ! ! ! &effectcd, ! ! ! ! ! ! ! &effectNode), ! ! ! "couldn't get effect node [time/pitch]");
Notice the type is AUFormatConverter, not AUEffect
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AudioUnitParameters.h// Parameters for AUNewTimePitchenum { ! ! // 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
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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
Monday, April 29, 13
Pitch shifting
• Pitch can vary, time does not
• Suitable for real-time sources, such as audio capture
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Demo: Pitch ShiftNew in iOS 6!
Monday, April 29, 13
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
Monday, April 29, 13
Demo: Rate ShiftNew in iOS 6!
Monday, April 29, 13
AUSplitter
AUSplitter
AUSomethingElse
AUSomethingElse
New in iOS 6!
Monday, April 29, 13
AUMatrixMixer
AUMatrixMixer
AUSomethingElse
AUSomethingElse
AUSomethingElse
AUSomethingElse
AUSomethingElse
New in iOS 6!
Monday, April 29, 13
Audio Queues(and the APIs that help them)
Monday, April 29, 13
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
Monday, April 29, 13
Audio Queue
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Audio Queue
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Audio Queue
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Audio Queue
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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
Monday, April 29, 13
Web Radio
• Project from Thursday’s workshop
• 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
Monday, April 29, 13
Parsing web radio
Monday, April 29, 13
Parsing web radio
NSData NSData
Packets Packets Packets Packets Packets
NSURLConnection delivers NSData buffers, containing audio and framing info. We pass it to Audio File Services.
Monday, April 29, 13
Parsing web radio
NSData NSData
Packets Packets Packets Packets Packets
Packets Packets
Packets Packets Packets
NSURLConnection delivers NSData buffers, containing audio and framing info. We pass it to Audio File Services.
Audio File Services calls us back with parsed packets of audio data.
Monday, April 29, 13
Parsing web radio
NSData NSData
Packets Packets Packets Packets Packets
Packets Packets
Packets Packets Packets
012Packets
PacketsPackets
PacketsPackets
Packets
NSURLConnection delivers NSData buffers, containing audio and framing info. We pass it to Audio File Services.
Audio File Services calls us back with parsed packets of audio data.
We create an AudioQueueBuffer with those packets and enqueue it for play-out.
Monday, April 29, 13
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”
Monday, April 29, 13
AudioQueue Tap!
http://www.last.fm/music/Spinal+TapMonday, April 29, 13
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
Monday, April 29, 13
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), ! ! ! ! "couldn't create AQ tap");
Notice that you receive maxFrames and tapFormat. These do not appear to be settable.
Monday, April 29, 13
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// ...
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So what should we do with the audio?
Monday, April 29, 13
So what should we do with the audio?
Let’s apply our pitch-shift effect
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Shouldn’t this work?
AUEffect
Monday, April 29, 13
Shouldn’t this work?
AUEffectAudioUnitRender()
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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?
Monday, April 29, 13
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
Monday, April 29, 13
invalidname’s convert-and-effect recipe
AUGenericOutputAUConverterAUEffectAUConverter
OSStatus converterInputRenderCallback (void *inRefCon,AudioUnitRenderActionFlags *ioActionFlags,const AudioTimeStamp *inTimeStamp,UInt32 inBusNumber,UInt32 inNumberFrames,AudioBufferList * ioData) {
CCFWebRadioPlayer *player = (__bridge CCFWebRadioPlayer*) inRefCon;
// read from bufferioData->mBuffers[0].mData = player.preRenderData;
return noErr;}
Note: red arrows are float format, yellow arrows are int
Monday, April 29, 13
How it works
• AUGraph: AUConverter → AUEffect → AUConverter → AUGenericOutput
• Top AUConverter is connected to a render callback function
Monday, April 29, 13
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.
Monday, April 29, 13
Yes, reallyThis 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);}
Monday, April 29, 13
Yes, really
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;}
This is the render callback that supplies data to the int→float converter
Monday, April 29, 13
Demo: AQ Tap + AUNewTimePitch
New in iOS 6!
Monday, April 29, 13
Monday, April 29, 13
Meanwhile in a mini-bus near
Copenhagan…
Monday, April 29, 13
Audiobus
Monday, April 29, 13
Audiobus
• Allows multiple audio apps to exchange data in realtime
• Works by sending raw data in MIDI
• Actually approved by Apple
• Actually supported in GarageBand
Monday, April 29, 13
Monday, April 29, 13
Monday, April 29, 13
Supporting Audiobus
• Get the SDK from audiob.us
• Enable background mode, add an audiobus-compatible URL scheme, get API key from audiob.us
• Create and use ABAudiobusController, ABOutputPort/ABInputPort, and ABAudiobusAudioUnitWrapper
Monday, April 29, 13
Wrapping up…
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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
Monday, April 29, 13
Q&A
• Slides will be posted to slideshare.net/invalidname
• Code will be linked from there and my blog
• Watch CocoaConf glassboard, @invalidname on Twitter/ADN, or [Time code]; blog for announcement
• Thanks!
Monday, April 29, 13