[DTL]

It is all done inside single blending engine for better speed. Any sequence of 'filters' in AVS takes lots of RAM for caching inbetween filters and for each thread and also the second main reason of single blending engine - it can load once all src and all ref frames blocks data from RAM to CPU L1D cache and make many processing not touching host RAM any more.

If you chain some filters in AVS each filter make full frame scan in some order so data is many time loaded from host RAM into CPU and it is much slower.

So for performance reasons it is better to make all processing for each input/output block in single (may be very complex) blending engine and not write some intermediate results in AVS-clips RAM objects and making final blend/merge in separate objects. Unfortunately AVS-filters can not interoperate image data on small chunks like blocks or samples - only total frames are requested by downstream filters from upstream. And total frame request invalidate most of caches (at least L1D as the fastest but only about <100 kBytes in size).

If IVS-mask is useful for some other scripting it can be special mode of MDegrainN to output this mask in some more nice form like grayscale 256 levels or just 1 black and white. Currently its output is designed only to check of mask placing over the frame data so it is not clean from image data.

I think for better understanding how old and current MDegrainN (MAnalyse + MDegrainN) is working and where many of adjustments params are passing it is good to create some structure scheme. May be will do in some form for documentation.

One sad issue with 'direct output' of IVS-mask: In better quality 'overlapped' mode of MdegrainN it is also generated for each block of 'overlapped blending space' and the blocks count in any overlapped mode are > blocks count in not overlapped mode (simple tesselation of frame to width/blocksizeH and height/blocksizeV number of blocks). So the IVS-mask in simple single frame form can not be outputted for good quality overlapping processing modes. Or some way of output of overlapped mask need to be designed (like doubling or quadrupling of output framerate to output each part of mask in separate frame). It is much more complex. It is also reason of using single blending engine instead of attempt to transfer mask via current AVS scripting interface based mostly on simple 'clips' objects of fixed frame size and may be expecting masks to be produced in same size.