[Libva] Get image data from VaapiSurface

[Sivaramkrishna]

Hi all,

I am trying to perform hardware accelerated decode of 720P h264 encoded 
stream using Gstreamer Vaapi decode and Vaapisink plugins .I am using 
ATI Radeon 5600 GPU .

My requirement is to get the image data from the Vaapi Surface after 
decoding .I want to perform some operations on this image like scaling 
,composing the two images .

As of now i tried to extract the image from the Vaapisurface by using 
the functions in Gstreamer Vaapi library ,

image = gst_vaapi_surface_derive_image(surf);

value = gst_vaapi_surface_get_image(surf,image);

the about functions were unsuccessful and i couldn't get the image data 
from the Vaapi surface .

Is there any way i can perform scaling and composing directly on the 
Vaapi surfaces without extracting the image data ?what do you suggest 
,should i use gstreamer vaapi plugins or libva API's directly to do the 
above mentioned tasks ?if i can work using libva API's ,can anyone 
explain me how to perform scaling and composing of two vaapi surfaces?

Any help is highly appreciated .

Thanks,
N Sivaramkrishna.