Hi,
This looks good. For calling NvBufferComposite(), please refer to code in the sample:
/usr/src/jetson_multimedia_api/samples/13_multi_camera/
Ideally the solution should work but uncertain if it can achieve target frame rate. Please also refer to this topic to run the engine at maximum clock:
Nvvideoconvert issue, nvvideoconvert in DS4 is better than Ds5? - #3 by DaneLLL