Calculating storage

[Robin Probyn]

Shooting HDX900 1080/60i.. recording Nanoflash XDCAM 422HD QT 50Mbps.. Long GOP..

Can 60i be treated as 30p re how much GB,s it will use up in a HDD.. I have a calculator which has 1080/30p and 1080/60p.. but no 60i..

many thanks

[Dan Keaton]

Dear Robin,

Unlike most other devices, when you specify a certain bit-rate in the nanoFlash, that is the bit-rate you get, regardless of the frame rate or if it is interlaced or progressive.

On our website, we have a simple table for you to determine approximate run times:

Media | Convergent Design

With the above link, you can determine how much footage will fit on a 64 GB card. Then you can calculate the GB's per minute of footage, then determine how many minutes you can get on your hard disk drive.

[Robin Probyn]

Ok thanks Dan..

[Dan Keaton]

Dear Robin,

If you tell me the details of your hard disk drive, or the formatted capacity, I will calcuate the number of minutes of footage that it can hold.

[Robin Probyn]

Hi Dan

Just a simple 320 GB HDD.. I would be using a MacBook.. with shotput pro 3 for the transfer.. 4 sound channels

Thanks

[Dan Keaton]

Dear Robin,

At 50 Mbps, you get approximately 160 minutes on a 64 GB card.

160/64 = 2.5 minutes per GB (approximately)

I am ignoring the fact that a 64 GB card may not have a full 64 GB of usable space.


A 320 GB Hard Disk Drive may have around 297 GB of formatted storage.

297 GB x 2.5 minutes per GB = 742.5 minutes.

Please consider these to be rough calculations.

[Robin Probyn]

Thanks Dan.. yes thats about the same as I got.

So the frames per sec e.g. 30p or 60p doesn't make any difference..? why is that? On my iphone app for calculating data storage,there is a difference between frame rates..?? confused..

Thanks

[Dan Keaton]

Dear Robin,

With other recorders or in-camera recording, the frame rate does matter.

For example, with DVCPro HD, the effective bit rate depends on the frame rate and it varies from 100 Mbps down to 40 Mbps.

With ProRes recording, the frame rate matters also.

With the nanoFlash the "bit rate per frame" actually increases when there are fewer frames per second.
Thus, when recording in 24p mode, one actually obtains a little higher quality since the number of bits allocated per frame is more than when recording 30 frames per second.

This ensures that the bits used per second remains constant regardless of the frame rate.

With the nanoFlash, when you specify 100 Mbps you actuall get 100 Mbps regardless of the frame rate.

Thus the calculations are easy.


Note: There is one exception: the very special 720p 60/50 > 30/25 mode.

In this mode, for technical reasons, we have to encode the frames first, then discard the duplicate frames.

One obtains the same quality per frame, at a given bit rate, as one would normally, but the actual bits used per second would be 1/2 the normal amount.

If desired, in the special 720p 60/50 >30/25 mode, one could actually use a higher bit-rate in the nanoFlash menu.

For example, in this mode, using CompactFlash cards that only work up to 220 Mbps, one could select 280 Mbps, if desired and it would work fine.

[Robin Probyn]

Hi Dan

Ok many thanks..

[Jeff DePonte]

Originally Posted by Robin Probyn

Just a simple 320 GB HDD.. I would be using a MacBook.. with shotput pro 3 for the transfer.. 4 sound channels

Hi Robyn,

I recently became aware of Shotput Pro, and you are the first person I know you uses it. I'm curious: why do you use it? Is it the automation aspect? I'd like to understand the workflow.

And, the 320GB HDD you mention: is this the internal HDD on your MacBook, or an external?

I recently acquired a Dell Mini 10v "Hackintosh" running Mac OS 10.6. I'm now using it as my backup host cpu in the field with external USB HDDs, although it does have a 160GB internal HDD that has 140GB free. The USB CF card reader that Convergent Design supply with the Nano is pretty quick!

Off-topic: I spent some time on Veteran's Day at Pearl Harbor visiting the USS Bowfin, a WWII submarine. It was fun trying to imagine how big those Japanese aircraft carrier submarines must have been!

Aloha,

Jeff

[Adam Stanislav]

Originally Posted by Robin Probyn

So the frames per sec e.g. 30p or 60p doesn't make any difference..? why is that?

I do not see how the frame rate could make any difference when you use Mbps as your measure. Mbps stands for megabits per second. It tells you how many megabits you end up with after you have compressed all of the frames in one second.

So, if you use 220 Mbps for example, you end up with 220 megabits each second whether those 220 megabits contain the compressed data of 24 frames, 25 frames, or 30 frames and whether they contain the compressed data of 1080p or 720p frames.

That also means that 24 fps will give you fewer compression artifacts than 25 fps or 30 fps because the uncompressed 24 fps stream contains less data than the uncompressed 25 fps or 30 fps stream, so the compression throws less of the original data away from the 24 frames than it does from the 25 frames, let alone the 30 frames.

So, to get the same quality from a 30 fps stream as you get from a 24 fps stream compressed at 180 Mbps, you would have to compress the 30 fps stream at 225 Mbps. This is only if you want the same quality per frame.

In reality, since 30 fps shows 30 frames in a second and 24 fps shows 24 frames in a second, you probably would not notice any difference visually because your brain has less time to look at each frame at 30 fps than at 24 fps. So, visually you should get more or less the same result from 180 Mbps regardless of the frame rate.

But if you were to examine individual frames as if they were static images, 24 fps will get you fewer compression artifacts than 30 fps compressed with the same bit rate.

OK, I'll stop now as I do not want to confuse you. Just remember the megabits per second measure the size of the data after it is compressed, so 220 megabits is 220 megabits in a second regardless of how many frames the 220 megabits contains.

[Andrew Stone]

A very useful and free iphone, ipod touch app is available that allows you to easily calculate the storage requirements for a variety of codecs and their various bitrates. There are a lot of standard image size/codec and bitrates listed but you can call up custom ones as well. It's called "AJA DataCalc" and you get it through Apple's "App Store". Aside from the "Daylight" app that tells you when the Golden Hour is for any given day of the year, it is the most used film app on my iPhone.

[Robin Probyn]

Hi Andrew

Yes thanks.. thats the app I have already.. but this does give different results for different frame rates ?

Unlike what Adam says?

Hi Jeff

I did a job earlier this year in Tokyo and the US data wrangler guy was using this software(version 2) there is now version 3.. the few small jobs I had done with the nano I was just dragging and dropping on the desktop.
Shotput pro is $99 but well worth it for worry warts like myself!! you get an easy interface.. you can see whats going on.. files are verified as they get transferred .. there is a report if there is any trouble you can see what and where.And also you can copy to multiple drives at the same time.
I guess for those with FCP or similar on their computers they can transfer straight into their edit workflow.. as i dont edit and will only be giving a HDD to the director shotput pro is a really good for peace of mind..
You can do allsorts of things with naming/renaming files also..

[Dan Keaton]

Dear Robin,

For AJA's devices, the frame rate matters.

For our nanoFlash and/or nano3D, the frame rate does not matter.
If you specify 100 Mbps, you get 100 Mbps.
(Above I noted the one exception.)

[Robin Probyn]

Hi Dan/Adam

Ah ok I get it.. didnt figure that was for their products only..

Thanks again