How to capture hdmi->usb by mhl

Let's say I connect my smartphone's micro USB port to a micro HDMI port of a video handycam, with a MHL cable.

I need to know:
- The pin mapping done by the mhl cable- namely what usb pin is connected to what hdmi pin (I couldn't find on the net).
- How can I capture the audio/video signal output by the camera, with the phone through its micro USB port (I want to write the driver for that).

We suppose the phone doesn't have a dedicated MHL chip (even if it had one, it would be for output from the phone not for input).
Also, I don't want to use Wi-Fi.

Any hint is appreciated.
Thanks.