Support for Voice Processing IO Audio Unit on Mac

[nanang]

Voice Processing IO Audio Unit is considered to provide nice features such as echo cancellation & AGC, it is supported since Mac OSX 10.7.

Our internal testing indicates that the EC performance is far more superior than any software EC. However, VPIO seems to work only with specific devices, thus requiring you to use the default/built-in audio I/O devices (i.e. it doesn't allow you to select your own devices). Application wishing to disable the hardware EC and use software EC instead can specify PJMEDIA_ECHO_USE_SW_ECHO in pjsua_media_config.ec_options (or MediaConfig.ecOptions in pjsua2).

*Limitation: only works in mono. *

[ming]

In 6094:

Fixed #1778: Support for Voice Processing IO Audio Unit on Mac

[ming]

In 6127:

Re #1778: Fixed incorrect calculation for stereo mode

[ming]

In 6128:

Re #1778: Temporarily disable VPIO on Mac for stereo due to recording sound defects.
Steps to reproduce:

• Revert this changeset
• Use pjsua to do sound loopback (cc 0 0) with --ec-tail=0 (VPIO disabled->audio fine) and ec-tail=1 (VPIO enabled->recording sound defects)

Several observations:

• Playback is totally fine in VPIO stereo mode.
• Defect more noticable in 44.1 kHz