The P2 data rate

Yuval Shrem

Yuval Shrem

Active member
Reading about the P2 cards, I couldn't help but calculating the data rate, and I must say that whatever I did, the numbers just didn't add up.
It seems that consistently, the data as it is stored on a P2 card only takes one 6th of the space it is supposed to take.

For example: DVC Pro-50 should store 50 MB per second with 60i, however, a quick look at the P2 chart shows that a 4GB card could hold 8 minutes of DVC-Pro-50 video footage.

50MB x 60sec X 8min = 24GB

So how the 24GB footage could fit in a 4GB P2 card ?????

This 1/6 ratio is consistent when calculating on a per-frame basis. Can anyone please explain this? can anyone solve this data rate riddle?

Thanks,

Yuval.
 
You got your bits and bytes mixed up.

50mbit per second is not the same as 50 MB per second.

Not sure what the exact conversion rate is but 50mbit per second should be about 6 MB.
 
ProjX's right -- you're mixing up megabits and megaBytes.

25 megabits per second = about 4 minutes per gigabyte (DV, DVCPRO25)
40 megabits per second = about 2.25 minutes per gigabyte (DVCPROHD 720/24p)
50 megabits per second = about 2 minutes per gigabyte (DVCPRO50)
100 megabits per second = about 1 minute per gigabyte (DVCPROHD 1080)


The numbers are not exactly on -- for example, you really should be able to get about 4.75 minutes per gigabyte in DV mode -- but I'm rounding the numbers down presuming that various metadata files will occupy a little bit of space.
 
Thanks!

Thanks!

Thanks for your helpful feedback! :)

It surly did eliminate a lot of confusion.
I was worried about data compassion…
I guess I shouldn’t worry about that then.
:beer:
 
Could one daisy chain via Firewire the HVX200 to a 12" powerbook with a high-speed mobile firewire 7200RPM 60GB drive INSTEAD of using the P2 cards? I realize that this is a clunky but inexpensive solution to those already owning a powerbook.

This appears to be the fastest mobile firewire drive on the market (See Below)
http://www.lacie.com/products/product.htm?pid=10555

(shooting at 24p 720p)
based on Barry's datarate above for shooting at 720p/24p would require a diskdrive to handle 40 megabits/sec or 5MB/s data transfer.

So the question I need to research is what is the data transfer rate for a Lacie 7200RPM portable firewire drive? Besides data transfer rate, is there any other reason that using a portable firewire drive to replace P2 as an ad hoc low cost solution besides the obvious? (at least until P2 prices come down after 12 months after release)
 
internal hard drives are fast enough

internal hard drives are fast enough

leofish said:
Could one daisy chain via Firewire the HVX200 to a 12" powerbook with a high-speed mobile firewire 7200RPM 60GB drive INSTEAD of using the P2 cards? I realize that this is a clunky but inexpensive solution to those already owning a powerbook.
Click to expand...

why even bother with a firewire drive except for occasional backups? you can throw a 60gb, 80gb, 100gb or greater 2.5" drive in your powerbook and capture directly in fcp. check out this 2.5" drive test on barefeats (last speed test on bottom shows mb/sec). all of the drives are nearly twice the required 12.5mb/sec:

http://www.barefeats.com/mini01c.html
 
leofish said:
Could one daisy chain via Firewire the HVX200 to a 12" powerbook with a high-speed mobile firewire 7200RPM 60GB drive INSTEAD of using the P2 cards? I realize that this is a clunky but inexpensive solution to those already owning a powerbook.
Click to expand...
Yes you could do exactly that.

Besides data transfer rate, is there any other reason that using a portable firewire drive to replace P2 as an ad hoc low cost solution besides the obvious? (at least until P2 prices come down after 12 months after release)
Click to expand...
For a low-cost alternative, this is a completely viable solution. As long as you can schlep the computer and drive around, you can do exactly what you're suggesting. Although I wouldn't use a powerbook, I'd get a PC-based laptop and use Serious Magic's HD Rack program (which hasn't even been announced yet, I'm just anticipating that they'll do it) so you get a full-screen monitor, waveform, vectorscope, disk recorder, and all sorts of other goodies.

If someone makes a comparable program for the mac, then the powerbook becomes just as good of an option.
 
thanks wigby and barry....great and helpful responses.

wigby, might want to have a spare firewire to avoid capture to main system drive using FCP but just tacking on a 12" Powerbook with 5200RPM 100GB drive is a lot cheaper than P2 right out of the gate.

HD Rack looks like it could be pretty sweet. might shape up to be the best option when HVX ships at year's end.
 
Barry_Green said:
If someone makes a comparable program for the mac, then the powerbook becomes just as good of an option.
Click to expand...

Final Cut Pro 5 is just that program with the added bonus of being a top editing app at the same time.

And from next year on when Apple switches to Intel processors, HD Rack will run natively on the new generation of Intel-Powerbooks as well.
 
PKraft said:
Final Cut Pro 5 is just that program with the added bonus of being a top editing app at the same time.

And from next year on when Apple switches to Intel processors, HD Rack will run natively on the new generation of Intel-Powerbooks as well.
Click to expand...
Several people have made the same comment regarding HD/DV Rack, that isn't the case. It would be fairly straight forward to recompile DV/Rack to run on a Mac today - its not the chips, it's the fact that OSX doesn't have (Mirosoft's) Direct X required for the graphic overlays. Even if OSX ran on intel's today you still coudn't run DV/HD Rack unless Apple is willing to license Direct X or Serious Magic is willing to re-write their graphics engine to accomodate OSX.

If I were Serious Magic I would not want to be the first on the block to make that transition. They could just cut to the chase and port it to the iPod... :)
 
ChuckS said:
Several people have made the same comment regarding HD/DV Rack, that isn't the case. It would be fairly straight forward to recompile DV/Rack to run on a Mac today - its not the chips, it's the fact that OSX doesn't have (Mirosoft's) Direct X required for the graphic overlays. Even if OSX ran on intel's today you still coudn't run DV/HD Rack unless Apple is willing to license Direct X or Serious Magic is willing to re-write their graphics engine to accomodate OSX.

If I were Serious Magic I would not want to be the first on the block to make that transition. They could just cut to the chase and port it to the iPod... :)
Click to expand...

The future Intel-Macs/Powerbooks are said to be double bootable which means you can also run Windows natively on that platform --> with Direct X being available then, what should hinder you to run DV/HD Rack on a Powerbook then?

BTW, there are already apps available that run both on PowerPC and Intel Macs. I have three of those here.
Fact is, it's a mostly a pretty straightforward recompile to make apps compatible for both platforms, and yes, there are Intel-Macs out there at developpers to do just that and test how easy it is to go that way. Nothing secret, nothing miraculous.
 
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