Overcrank hype: what's the deal?

megabit wrote on 5/28/2010, 6:28 AM

OK, so I can overcrank my EX1 at 720/25p to 50 fps (or do the same on the nanoFlash) - but what is so special about it?

What makes me ask this question to those more knowledgeable is that - in fact - I'm getting EXACTLY the same slow-motion results from Vegas, by simply by 2x stretching clips recorded normally, i.e. at 720/50p, in the 720/25p project.

Is there anything I'm missing, that could yield better results from over-cranking?

Comments

farss wrote on 5/28/2010, 6:41 AM

I don't think I really understand your question.

If you record at 50fps flagged as 25fps then recording at 50fps and slowing that down to 25fps in Vegas or anything else the result should be exactly the same, in theory with one exception.

If you use S&Q motion in the EX it writes at the full data rate.
720p50 is written at 35Mbps. Overcrank 25fps to 50fps and it writes at around 70Mbps. Whethere you notice any difference or not could depend on many things.

Bob.

richard-courtney wrote on 5/28/2010, 6:42 AM

That's a good question. Is there a difference capturing an image at 50fps or using
an image captured at 25fps but making it appear on screen twice as long?

Depends on how fast the subject is moving.

megabit wrote on 5/28/2010, 7:04 AM

Bob,

You have understood my doubts correctly (even though I might have expressed them not quite so...).

Anyway, when I studied the 2 methods VERY carefully indeed, I DID notice some quality advantage using 220 Mbps I-frame overcranked clip from the nanoFlash (mainly due to the 4:2:2 color resolution).

Perhaps - with really lots of movement - I could also see some improvement in the EX1's own overcranked clips (over the 35 Mbps one stretched 200%).

OK, the effective bitrate difference sort of answers my question.

Piotr

K-Decisive wrote on 5/28/2010, 7:34 AM

You should be able to get it alot smoother by doing it in camera. Try this, when you shoot overcranked, make sure the shutter is 1/50, 1/60 or maybe a little faster, but not 1/24. you will get much cleaner frames. If you just stretch, it's either blurring between every other frame or just repeating every frame twice. When I do slow-mo I shoot at 60fps on the HVX.

megabit wrote on 5/28/2010, 8:23 AM

Of course - when stretching, I entered the playback rate=0.5000 precisely and disabled resample - so I guess Vegas was doubling frames...

farss wrote on 5/28/2010, 2:04 PM

Vegas is NOT doubling frames.
In both cases the camera records 50fps, in one case (S&Q) the playback rate is flagged as 25fps, the other (720p50) the playback rate is flagged as 50fps. In the later case by setting the playback rate to 0.5000 Vegas will not interpolate frames, it will simply playback 50fps at 25fps i.e. change the playback rate.

One obvious advantage of S&Q is you can set the framerate to numbers such as 43fps, just make certain you have flicker free lighting. Trying to shoot 60fps in Region50 can be a challenge.

Bob.

megabit wrote on 5/28/2010, 6:56 PM

"In the later case by setting the playback rate to 0.5000 Vegas will not interpolate frames, it will simply playback 50fps at 25fps i.e. change the playback rate."

Yes you're right, Bob - I got mistaken by the suggestion from the previous poster who implied interpolation; hence I wrongly stated that Vegas rather doubles frames, if anything.

However, all this is not my point - I'm just slightly dismayed that motion-wise, the result of 50p stretched and played back at 25 fps is not that much worse than that of S&Q (overcranked) material. I was expecting overcrank to give much better results; it certainly will show the edge with a lot of movement or otherwise stretching the codec, thanks to its higher bitrate at acquisition stage.

Plus of course, similarly overcranked clips from the nanoFlash should be better still, due to even higher bitrates possible and 422 color resolution.

Piotr