Y4M header C

Hello /prog,
I need help parsing the header of a y4m file.
I took a look at the y4m.c file from the link below and i cannot understand what are all these 4 inputs for in the open_file func. The task is just to read the header.
Thanks in advance.

http://www.v.8mv.net/2010/mar/x264/input/y4m.c

One is filename, the three others are handlers and since none of them are declared const I assume they are output handlers.

So you should just put some of the required structures on the stack and then pass the address on to the function.

But from which one do i get the whole header?

>>3
Read the documentation you fucking mouthbreather.

header is defined on line 42
it gets set in lines 63 to 77