AudioDeviceDetection

Version 8 (Adrian Georgescu, 07/25/2010 02:22 pm)

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= Audio Device Detection =
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[[TOC(Design*, AudioDeviceDetection, depth=1)]]
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== Introduction ==
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The idea behind audio device detection is to allow SIP users to switch headphones, speakers or microphones as they are plugged or unplugged from the computer.
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Many SIP applications allow this. Some require to restart the application, while others can detect it while running. SIP SIMPLE client can currently detect hotplugged devices in Mac OS X platforms.
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== Goal ==
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The ultimate goal is to enable SIP SIMPLE client applications to detect audio device changes on the fly in all currently supported platforms, with the most immediate priority being [ticket:117 Windows platform].
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== Schematic Overview ==
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[[Image(wiki:AudioDeviceDetection:SipSimpleAudioDevicesChange.png, width=1024)]]
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== Required Modifications ==
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After a first analysis of the SIP SIMPLE client SDK, these are the necessary code modifications:
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=== PortAudio modifications ===
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First, it's necessary to hook up into the host OS multimedia system in order to get notified when new devices are added or old ones removed. If the OS doesn't provide a notification API, a poll loop with sensible frequency settings will need to be used.
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 * Currently, this is already achieved in Mac OS X through the `AudioHardwareAddPropertyListener` function in Core Audio API.
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 * In Windows platforms (under `WMME` hostapi), `WM_DEVICECHANGE` notification or similar methods may be used (proper research of `mmsystem` API is pending).
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 * Each of the rest of platforms (or corresponding hostapis) will need their own implementations too.
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Second, the hostapi needs to react to the `DevicesChanged` notification, by updating the internal audio devices data (after which PortAudio will proceed to notify upper layers about the availability of a new devices list). This is achieved through the `RescanDevices` function.
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 * Mac OS X hostapi, Audiocore, already updates its internal devices list with `RescanDevices()`.
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 * Windows platform lacks such a function. [http://osdir.com/ml/audio.portaudio.devel/2007-02/msg00094.html Partial implementations] have been provided in PortAudio mailing list, but have not yet been integrated into SIP SIMPLE client official releases.
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 * The rest of platforms will need their own implementations too.
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=== SIP SIMPLE client modifications ===
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The Windows version of SIP SIMPLE client SDK may need some very minor tweaks.
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At first sight, `AudioDevicesDidChange` and `DefaultAudioDeviceDidChange` observers have to be added to `Application` implementation.