Without giving details on the hardware you're trying to run it on, it's difficult to give recommendations.
Firstly, there is no such thing as 1080p25. There is 1080p24/50/60. If you have "1080p25" as an option in your drivers, it is most likely outputting a 1080i50 signal, or a signal that very few displays will sync to.
If you are watching films, I would suggest outputting 1080p24 and using VideoClock anyway.
Unless your system can't handle madVR's scaling
at all I would set your output options to 1080p24/50/60 (or just 1080p24/60 if using VideoClock) rather than outputting video at its "native" resolution. (MC18 cannot output DVDs unscaled, even if you set it to 720x576)
I would recommend
not using the hardware acceleration option in MC18 if your CPU can handle the decoding, because that's a power saving option rather than a performance one in most cases. Once you have madVR running smoothly, you can try it again.
As for madVR performance, when it is running you can hit CTRL+J to view the on-screen statistics and check for dropped/delayed/repeated frames. Once playback has started (give it 10s) you should not experience any of these. (there will be some at the start and you can hit CTRL+R to reset the stats)
I would suggest starting by setting all scaling options to Bilinear, as this is the least demanding scaling option in madVR. (even less than DXVA - which is actually quite taxing on my system compared to many of the other options) If
this doesn't run smoothly, start enabling the "trade quality for performance" options one at a time, working your way down from the top.
If Bilinear is running smoothly, you want to work your way up the luma/image upscaling options. Generally the performance tiers are:
Lowest complexity:Nearest Neighbor
Bilinear
Low complexity:Mitchell-Netravali
Catmull-Rom
Bicubic
SoftCubic
Medium complexity:Lanczos
Spline
High complexity:Anti-ringing Lanczos/Spline
Jinc
Anti-ringing Jinc
Anything inside those groups should have the same performance, except the high complexity where it does get more demanding as you work down the list.
While you have the option of 3/4/8-tap scaling with some of the more complex algorithms, the best results both from an image quality and a performance standpoint, are achieved at 3-taps.
Which algorithm you pick depends on your preference between sharpness, ringing, and aliasing. Most algorithms only fare well in two of those categories so you are compromising on the third.
Personally I like a low-aliasing, low ringing image, and don't mind if that comes at the cost of sharpness, so I like SoftCubic 80 for DVD playback. (most commercial DVDs are full of compression artefacts/ringing in my experience)
Others may prefer how Mitchell-Netravali or something else looks.
Once you have found the scaling algorithm that performs well and looks good to you, then you may wish to try increasing the chroma scaling options. For that, I would suggest only trying these:
- Bilinear
- Mitchell-Netravali
- Bicubic 75 Anti-Ringing
- Lanczos 3 Anti-Ringing
- Jinc 3 Anti-Ringing
I do not think the other options are a good choice for chroma scaling. (either too soft, or too much ringing)
Chroma scaling is far less than Luma (image) scaling, so you are best to leave it at bilinear if that allows you to use a better Luma option unless you are particularly sensitive to it.
There is extensive discussion of which algorithms are best
over at Doom9. If you search through my post history there, you will find a number of large posts going into detail about it.