Android : Access video frame buffer in callback in HAL 1.0

I am working on the camera HAL 1.0 for Android. I have read in the documentation that the video frames are returned in the camera_data_timestamp_callback with a CAMERA_MSG_VIDEO_FRAME message.

When I check the data in the camera_memory_t* parameter, there are only 8 bytes of data in it. My questions are, what are these 8 bytes and how can I use this data to access the actual buffer with the video frame data?