ffdshow scaling colour issue & post-processing alternative?

[DragonQ]

Hi all, I have two questions regarding post-processing.

Firstly, I have MediaPortal set up to use ffdshow raw video filter, which itself is set to resize any video below 720p with Lanczos. LAV Video decodes and deinterlaces via CUVID, then ffdshow resizes if necessary (SD sources). However, for some reason, enabling this resizing filter changes the colour output of the video. I can see the colours get darker when I tick the resize box and get lighter again when I untick it, in real time. Is there any reason why this would happen? I have the output colour space set to "auto".

Secondly, ffdshow is rather old and no longer supported. Are there any newer raw video filters that offer superior functionality (e.g. better scaling algorithms)? Ideally I'd just use MadVR but unfortunately MediaPortal doesn't support it.

Thanks for any advice!

[vivan]

SD and HD video use different color matrices (BT.601 and BT.709). Video renderer believes that it should use BT.709 for RGB conversion since it gets video with HD resolution while it should use BT.601, which leads to wrong colors.
Probably the easiest way to solve this would be to force LAV to convert video to RGB (untick everything in output formats except RGB). If perfomance impact will be too high - do this with ffdshow instead (I haven't been using it for a long time, but I believe it has such an option).

Yeah, getting madVR support will be ideal...

[DragonQ]

Thanks for that, vivan. I've set ffdshow to output RGB32 only and that fixes the issue. I was originally confused because changing settings seemed to have no effect but I needed to restart the video stream after changing the output format. Now, if I switch between BT.601/Auto and BT.709 in ffdshow, I can see the difference in colour immediately. CPU usage for 576i/25 is now ~50% but that's OK. Setting LAV Filters to output RGB32 pushes this to 85%, which is too high for everyday use IMO.