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Frame rate interpolation

 
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Sesse
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PostPosted: Fri Jan 03, 2003 8:51 am    Post subject: Frame rate interpolation Reply with quote

A friend of mine needs to convert some PAL video (ie. 50Hz, interlaced) to NTSC (ie. 60Hz), but couldn't find any decent software to do it (Premiere blends entire frames instead of fields, and most other software either was very limited or expensive). What did you guys use? Motion vectors etc. would probably be a plus but definitely no need -- low or zero price would be a very big plus. The ability to read a standard AVI file (as opposed to "DV only" etc.) would also be a very big plus. :-)
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Trixter
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PostPosted: Fri Jan 03, 2003 12:00 pm    Post subject: Reply with quote

One of the ways I achieved motion interpolation at extremely low cost was to use DynaPel's MotionPerfect (http://www.dynapel.com/). It's $29. It has flaws; it won't work with AVI files over 2 gig, and it doesn't grok interlaced footage. But if you need to convert 5-minute or less segments, you can work around those flaws like this: Convert your footage with virtualdub + avisynth to a progressive double-rate .AVI (http://home.bip.net/gunnart/video/#deinterlacesmooth is the best way) and feed that to MotionPerfect, let it convert, and then convert it back to interlaced footage with avisynth again. You trade your time and skill for money, basically. Wink Download the trial of Motion Perfect and do a convertion on an 8-second clip using the above method to see if it works for you.

If you need conversion longer than five minutes, you have several field-based alternatives:

- Canopus Procoder
- Adobe After Effects

...or you have some motion-interpolation options:

- Realviz ReTimer
- Reelsmart Twixtor

The latter being expensive, of course.

There are also hardware standards converters with motion-compensation circuitry, but they cost upwards of $20,000 (Folsom) and are meant for high-end broadcast applications. Otherwise, field-based hardware standards converters range from $1100 to $5000 like the Sony DSC-1024 (king of all scan converters, used heavily at demoparties to convert ntsc/pal/vga to whatever the projector supports).

PS: There is an intriguing product at http://www.dvunlimited.com/ that claims to support both field and motion and is very cheap, only $98. But I have never used it, and it only supports 720x480 (NTSC) or 720x576 (PAL) DV.
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Sesse
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PostPosted: Fri Jan 03, 2003 12:11 pm    Post subject: Reply with quote

Thanks, I'll pass the information on. :-) I think the last product you mention already was tried and found a) too expensive (this is for personal use, not DVD mastering :-) ), and b) not good enough (took DV only, and took no frameserving from Premiere etc.). I might be throwing together a simple VirtualDub filter or something if MotionPerfect doesn't do the trick, but I think this will be good enough. :-)
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Trixter
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PostPosted: Fri Jan 03, 2003 2:36 pm    Post subject: Reply with quote

Glad I could help. Here's some more notes:

- MotionPerfect (and any motion vectoring/interpolation method) easily provides the best results, but can result in sometimes bizarre artifacts and also easily has the highest rendering time. Expect at least a second per frame.

- Field-based interpolation isn't necessarily that bad -- in fact, if you have medium-to-low-motion footage, the results are just as good if not better. (Better meaning that if you have a lot of noise in your footage, the blending that occurs reduces the noise.)

- Canopus Procoder has measurably better NTSC<-->PAL conversion than After Effects. I'm still investigating why, but I believe it is interpolating fields line-by-line, as opposed to After Effects, which interpolates all fields in a frame by the same value.

- Writing a VirtualDub filter to do this is currently impossible because VirtualDub filters cannot insert or remove frames. You would be better off writing an avisynth filter.

- Don't get unreasonable Smile Meaning, don't expect everything to work like Virtualdub and avisynth, etc. The tool I mentioned previously is a good tool; don't damn it just because "you can't frameserve" or something. Finding a motion vectoring tool for $29 that could be worked with was a godsend -- the best products in this category cost $8000.

For an example of MotionPerfect, watch the end vector fly-by of 2nd Reality in MindCandy. If it looks significantly smoother than the original, that's because it is (up-synthesized to 60fps). Wink However, the eagle-eyed will notice two interpolation errors in the first ten seconds of the footage.
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