Hi,
You can call NvbufferComposite() in jetson_multimedia_api. And there is constraint in maximum video planes:
/**
* Defines the maximum number of input video frames that can be used for composition.
*/
#define MAX_COMPOSITE_FRAME 16
For Jetson Nano/TX1, the constraint is 8. Please check
[mmapi] how many input buffer is supported by function "NvBufferComposite" - #5 by DaneLLL