push_video_context

declaration:

    function push_video_context() => context_index;

store the current VID context on a stack, return the current stack index.
returns -1 on failure (stack full).

related functions:
[pop_video_context] [system_context_size] [current_context_usage]

caveats:
There's a static amount of possible stacks, although the number of elements allowed in new stack frames can be changed dynamically.