Success with mcbob and mvflowfps - thank you!

[2Bdecided]

It seems that I only ever come here with problems(!), so I thought I'd share my gratitude to the authors of these filters (and their component parts) because they're working well for me.

I've shared some video on another forum to try to show that 50i interlaced video is very useable/versatile, and the whole world doesn't have to switch to 24p!

http://www.hv20.com/showthread.php?t=2876

btw, mcbob is great for getting nice screen shots! I'm sure quite a few will be added to my digital photo collection, and printed to 6x4 to give to relatives for Christmas. Obviously I'm talking about snaps captured from videos of my kids, not the photo of a roundabout in the above thread!

Cheers,
David.

[morsa]

:script:

[2Bdecided]

What, you mean...
mpeg2source("myfile.d2v")
mcbob()? It's not very exciting! ;) I added ConvertToYUY2(interlaced=false) so I could save to HuffYUV.

I grabbed frame captures just using "copy source to clipboard" in VirtualDub, and resized to square pixel in CorelPhotoPaint. There are plenty of other ways of doing both.

mvflowfps from here:
http://forum.doom9.org/showthread.php?t=130332

24p version using this:
avisource("50i mcbob.avi") # i.e. the output from mcbob() saved to file

# Get motion vectors...
source=last
backward_vec = source.MVAnalyse(isb = true, truemotion=true, pel=2, idx=1, divide=2)
forward_vec = source.MVAnalyse(isb = false, truemotion=true, pel=2, idx=1, divide=2)

# Change frame rate and blur
source.MVFlowFps(backward_vec,forward_vec,num=600,den=1,idx=1)
temporalsoften(10,255,255,mode=1)
selectevery(25,0)

Strictly speaking, I think the temporal soften should be over 12-13 frames, not 10, but I didn't like that much blur. I don't actually like the blur anyway - I would never use 24p - but I was illustrating that you can shoot in 50i and then convert to 24p without major problems later if you want to - it's painfully slow though!

The point was I tried to shoot the same scene in 50i and real 24p, and then simulate 24p from 50i and see how close it came. It's not bad at all.

I wasn't convinced by MVFlowBlur, but maybe I didn't play with it enough.

Cheers,
David.

[anton_foy]

The result is very nice but why cant you just deinterlace to 25p from 50i and then changefps to 24? Then change the length (pitch) of the sound.

[2Bdecided]

You wouldn't get "correct" motion blur that way. My aim was to simulate real 24p, having comparable real 25p available as a reference, which I used to judge the result. The "real" 25p has bucket loads of motion blur, having been "filmed" with a 1/50th shutter speed.

Some people like this "look", apparently.

Cheers,
David.

[*.mp4 guy]

The reason people like that look (or atleast why I do) is because it helps keep stuttering at bay, at film frame rates. 25P with 1/50 shutter will have almost completely fluid motion (half of all motion is captured, but alot is mushed together into the same space, causing blur), contrast with 25p with 1/1000 shutter (relatively common), where only 1/40 of all motion is recorded, it has 20 times the temporal definition, and 20 times the judder (the temporal analog of spatial aliasing). Usually the brain fills in the gaps between frames, both adding its own motion blur, and guessing (very well) what happens between frames, but when the inconsistencies (motion) between frames is to great, the brain starts interpreting the "video" as a series of still pictures, and the illusion is ruined. using slow shutter speeds effectively applies a linear blending lowpass to the temporal dimension of the video, sacrificing spatial and temporal detail information for temporal fluidity information, thus keeping the illusion of motion at lower frame rates and/or during faster motion.

Basically you want to use the fastest shutter you can that will always produce smooth motion in your video, for some footage 1/50 is extreme overkill, and sometimes it may not be enough.

[anton_foy]

Im pretty sure that you would get the correct amount of blur if you shoot 50i with a 1/50 shutter and deint to 25p then slowdown to 24 fps. The shutter would be 1/48 now right?
For 25p or 50i the shutter should never be less than 1/50 unless you settle for a Saving Private Ryan-look or slowmotion you can use 1/100 or more. Less than 1/50 will give that crappy videocamcorder-feeling even though Collateral and Apocalypto uses it in some shots it looks like shit IMO.

[2Bdecided]

Im pretty sure that you would get the correct amount of blur if you shoot 50i with a 1/50 shutter and deint to 25p then slowdown to 24 fps. The shutter would be 1/48 now right?Yes, if the goal is to get 25p from a camcorder which doesn't have 25p, then you could force the shutter speed to 1/50th, mcbob the result, and drop every second frame. You might need an ND filter, otherwise forcing 1/50th in bright light is going to force a very (sometimes impossibly) narrow aperture.


Most camcorders shooting 50i in auto mode don't use 1/50th (unless there's very little light), which is a good thing, because the result has less motion blur at higher shutter speeds. I know stupidly high shutter speeds give strobing ("Saving Private Ryan" look), but something like 1/120th is a good compromise. Also, you can't get useable stills from 1/50th, while you can at higher shutter speeds.

The point of this experiment was to see if it was possible to produce footage at 50i which was optimum for 50i, but could be re-purposed for 24p/25p to a standard that was almost indistinguishable from native 25p. It seems, with AVIsynth, that it is - if you can wait a very long time for the processing to complete!

Cheers,
David.