Video API for PJSUA-LIB

[bennylp]

PJSUA-LIB video API specification:

1. Video Device Enumeration API

Specifications:

1. query device count
2. query device names
3. hotswap support?

2. Video Call API

Specifications:

1. enable or disable video when initiating call
2. enable or disable video when receiving call
3. choose which device to use for video call
4. add and remove video media stream during the call
5. change which device to use during the call
6. hide remote video window
7. move and/or resize video window

3. Video Capture Preview API

Specifications:

1. start and stop preview for the specified camera device, independent of calls
2. preview more than one capture devices independently
3. move and/or resize preview window

4. Media Info and Statistic API

The new API can be used for both audio and video.

Specifications:

1. query the number of media streams in a call
2. query the media stream info
3. query the media stream statistic
4. query the media transport info/statistic
5. move pjsua function that dumps call statistic (i.e. "dq" command) to a separate size, to reduce footprint for apps that don't use it.

5. Notification API

Nothing special for video. Update in media status is reported in on_media_state() callback as usual. Application may use media status API to query about video status.