Function drmtap_set_output_buffer 

pub unsafe extern "C" fn drmtap_set_output_buffer(
    ctx: *mut drmtap_ctx,
    dst: *mut c_void,
    len: usize,
) -> c_int

Point the conversion paths at a caller-owned buffer instead of a library-owned one, so a consumer that must end up with the pixels in its own memory does not copy the frame.

dst must stay valid for as long as it is set AND for as long as any frame pointing into it is held; libdrmtap never frees or reallocates it. Pass a null dst (with any len) to go back to the library buffer. A frame needing more than len bytes is refused with -ENOSPC and dst is left untouched, so a short frame can never be mistaken for a complete one. Size dst from a real frame’s stride * height, not width * height * 4: the CPU deswizzle keeps the source stride, which on a padded scanout is wider than the visible width.