New PJSUA & PJSUA2 APIs for instantiating extra audio device

[nanang]

The APIs will be useful for application that needs to work with multiple sound devices concurrently. It can also help application to simplify the tasks of improving media framework clock as described here.

Specifications

1. Audio device configuration settings to be supported:
   • PJSUA: ​pjmedia_snd_port_param.
   • PJSUA2: only playback and record device IDs.
2. Application can apply further settings whenever needed by:
   • PJSUA: querying the sound device port and apply further settings directly to it using PJMEDIA Sound Device Port APIs.
   • PJSUA2: inheriting class ExtraAudioDevice and apply the settings using the same approach as PJSUA above. This needs be done in C++.
3. Audio device must be registered to the conference bridge:
   • PJSUA: it must have API to query the conference bridge port.
   • PJSUA2: it must be a descendant of ​AudioMedia.

Sample code using PJSUA

enum { EXTRA_SND_DEV_ID  = 3; };

pjmedia_snd_port_param ext_param;
pjsua_ext_snd_dev *ext_snd_dev;
pjsua_conf_port_id ext_id;

/* Generate params (with default values) */
status = pjmedia_snd_port_param_default(&ext_param);
status = pjmedia_aud_dev_default_param(EXTRA_SND_DEV_ID, &ext_param.base);

/* Create the extra audio device */
status = pjsua_ext_snd_dev_create(&ext_param, &ext_snd_dev);
ext_id = pjsua_ext_snd_dev_get_conf_port(ext_snd_dev);

/* Connect extra audio dev mic to main audio dev */
status = pjsua_conf_connect(ext_id, 0);

/* Connect main audio dev mic to extra audio dev */
status = pjsua_conf_connect(0, ext_id);

...

/* Destroy extra audio dev (after no longer used) */
pjsua_ext_snd_dev_destroy(ext_snd_dev);

Sample code using PJSUA2

/* Use Null Audio Device as main media clock. This is useful for improving
 * media clock (see also https://trac.pjsip.org/repos/wiki/FAQ#tx-timing)
 * especially when sound device clock is jittery.
 */
ep.audDevManager().setNullDev();

/* Install extra audio device */
ExtraAudioDevice *auddev2 = new ExtraAudioDevice(-1, -1);
try {
    auddev2->open();
} catch (...) {
    std::cout << "Extra sound device failed" << std::endl;
}

/* Create WAV player and play the WAV to extra audio speaker */
AudioMediaPlayer amp;
amp.createPlayer(PATH_TO_WAV_FILE);
if (auddev2->isOpened())
    amp.startTransmit(*auddev2);

/* Wait for the WAV playback */
pj_thread_sleep(5000);

...

/* Destroy extra audio device (after no longer used) */
delete auddev2;

[nanang]

In 5717:

Close #2077: New PJSUA & PJSUA2 APIs for instantiating extra audio device.