Function roi_regions 

fn roi_regions(
    attribute: Option<u32>,
    hardware: Hardware,
    entrypoint: VAEntrypoint,
    cbr: bool,
) -> u32

The regions of interest a frame may name (Negotiated::roi_regions), from the driver’s VAConfigAttribEncROI: none where it reports none, or at a constant rate whose rate control takes no quantizer deltas (bit 9). On Intel’s low-power entry point at a constant quantizer no more than INTEL_VDENC_NATIVE_ROI: iHD’s VDEnc from Gen9 to Gen12 copies the delta of every region it is handed into a stack array of three when they share at most three deltas, which one refinement always does, so a fourth region writes past it and a frame naming a dozen aborted the process on __stack_chk_fail inside vaEndPicture (N97, a window dragged at 144 fps). Its rate control hands the regions to the firmware instead.