Decoding efficiency optimization: Copy decoded video frame(video memory) into system memory

hi.

I tested with sample_decode (./sample_decode_drm h264 -i intel_hw_test.h264 -o output.yuv -hw -vaapi),  that efficiency is very low.  

the test data:

• 720p video, decoding 15 frame per second and cpu100%  (total cpu400%).
• When I removed the write file operation(m_FileWriter.WriteNextFrame (frame)), decoding 1700 frames per second and cpu40%. 
• if I use memcpy operation to replace write file operation, decoding 80 frames per second and cpu100%.

So i guess , copy one frame from video memory to system memory is Performance bottlenecks.

My question is:

1. My guess is correct?
2. Is there a good way to enhance the efficiency of decoding?  My requirement: decoding 200 frame per second and  consume less CPU.

thanks.

hang.liu