How to down-rate 60p to 25p?

General questions or discussion about HandBrake, Video and/or audio transcoding, trends etc.
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piula
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How to down-rate 60p to 25p?

Post by piula »

I have a video which has been "upframed" (how do you call that?) from 25p to 60p. There hasn't been any frame interpolation, only simple frame repetition. So the picture sequence is AABBBCCDDDEEFFFGGHHH...

I want to get rid of the redundant frames by using "--cfr --rate 25". I'd assume handbrake using each 2nd, 3rd, 2nd, 3rd... frame for the output video.

The problem is that imho this can lead either to a correct or to a wrong result, depending on whether the algorithm starts in a 2-frame-block or in a 3-frame-block:

AABBBCCDDDEEFFFGGHHH --> correct ABCDEFGH
AABBBCCDDDEEFFFGGHHH --> correct ABCDEFGH
AABBBCCDDDEEFFFGGHHH --> wrong BBDDFFHH
AABBBCCDDDEEFFFGGHHH --> correct ABCDEFGH
AABBBCCDDDEEFFFGGHHH --> correct ABCDEFGH

So there is a 1:4 chance for getting a wrong picture sequence in the output file.

Does handbrake detect this situation or is there some other advice for ensuring that the proper frames are taken?
mduell
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Re: How to down-rate 60p to 25p?

Post by mduell »

HB doesn't detect it. Try it with HB to see if it does what you want.

If it doesn't, you'll probably need to use ffmpeg or avisynth for more control over the frame selection.
musicvid
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Re: How to down-rate 60p to 25p?

Post by musicvid »

Content deleted -- wrong answer.
Last edited by musicvid on Mon Oct 05, 2020 4:54 pm, edited 1 time in total.
mduell
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Re: How to down-rate 60p to 25p?

Post by mduell »

He's dealing with frame duplicated content, not native 60p content.
musicvid
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Re: How to down-rate 60p to 25p?

Post by musicvid »

Sorry for not reading carefully.

Here is a recent example of Handbrake getting it correctly with its "dumb" drop/dupe behavior. Specify "Constant" with your new frame rate. Either it works or it doesn't.
viewtopic.php?f=6&t=40524&p=192488&hili ... pe#p192488
If it doesn't work, VirtualDub will definitely do the trick with its available filters.
piula
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Re: How to down-rate 60p to 25p?

Post by piula »

Ok, thanks for helping me. I'll have a look at VirtualDub then.
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Rodeo
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Re: How to down-rate 60p to 25p?

Post by Rodeo »

HandBrake does dumb frame duplication but it also does feature basic frame similarity analysis for "smart" frame dropping. When it works, it works, but indeed, there's no guarantees it will.
musicvid
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Re: How to down-rate 60p to 25p?

Post by musicvid »

by Rodeo » Mon Oct 05, 2020 12:28 pm
HandBrake does dumb frame duplication but it also does feature basic frame similarity analysis for "smart" frame dropping. When it works, it works, but indeed, there's no guarantees it will.
Thanks for that, @Rodeo, I didn't know about that feature.
I suggest you try it in Handbrake first, as that is the simplest.

Here are the original Donald Graft VirtualDub filters, going back to ca. 2002.
http://rationalqm.us/mine.html#virtualdub
There are doubtless many newer VDub filters available, but you need to hunt around, maybe Videohelp has a compendium.
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