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Old December 26th, 2010, 04:27 PM   #1
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bit-rate in different frame rates

Since the bit-rate is per second, with higher frame-rates the bit-rate per frame will be lower. For highest quality I-Fo @ 280 mb/s is recommended. Am I right that when shooting in Pal area with 25 fps using 220 mb/s will be more or less equal to using 280 mb/s in NTSC area with 30 fps? (I realize that 220/25 is not exactly the same as 280/30, but I just mean to ask if lowering the frame-rate allows you to lower the bit-rate accordingly to get the same quality)
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Old December 26th, 2010, 04:38 PM   #2
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Dear Cees,

As far as I know, the nanoFlash is unique in almost always giving you the bit-rate that you requested, regardless of the frame rate.

So, yes, if you are shooting in 24p, the number of bits allocated to each frame is slightly higher than if you were shooting 30p.

And yes, you could take advantage of this fact, if you wish.

I calculate, (280 * 25) / 30 = 233.33 Mbps.

But, I would just pick out a bit-rate that you want to use, and use regardless of your frame rate.


In just a few cases, we have to run the incoming video stream through the Sony Codec, then, for example, discard duplicate frames.
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Old December 27th, 2010, 10:07 AM   #3
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Quote:
Originally Posted by Cees van Kempen View Post
Since the bit-rate is per second, with higher frame-rates the bit-rate per frame will be lower.
Most compression codecs are looking at the changes between frames. At a higher frame rate, the changes between frames are smaller. This leads to a non-obvious conclusion -- that bit rate is largely independent of frame rate. Depending on codec of course.

There's a pretty good explanation in considerably more depth in another thread on this board. I don't remember where and didn't book mark it. But some searching on your part should pull it out. Just a couple of months ago IIRC.
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Old December 28th, 2010, 05:15 PM   #4
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Quote:
Originally Posted by Cees van Kempen View Post
Am I right that when shooting in Pal area with 25 fps using 220 mb/s will be more or less equal to using 280 mb/s in NTSC area with 30 fps? )
Yes, basically is like that.
At equal data-rate, a p25 movie can allocate some 17% more info per picture, than a p30 movie.
This doesn't happens only with the NANO, but with every single codec.
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