Philippe Gorley authored Feb 19, 2019 and Adrien Béraud committed Mar 26, 2019

Sets up video streams upon receiving the first video frame. Audio
streams are still initialized as soon as possible.

This allows a video encoder to use the pixel format of its received
frames, and to set up a hardware transcoding pipeline if it receives
a hardware frame.

Change-Id: I622fc44b6096d63d7423837d2f2ec15680548a83