What's the math to calculate storage?
- Thread starter Two_Times
- Start date
I forgot the math
heres a storage chart
HE 1440x1080 60i | 6mbps
3 hrs (8gb)- 6 hrs(16gb) - 12hrs(32gb)
HG 1920 x 1080 60i | 13mbps
1hr 15 mins- 2 hrs 30 mins- 5hrs 15mins
HA 1920 x 1080 60i | 17mbps
1 hr - 2 hrs - 4hrs
PH 1920x1080 60i, 30p, 24p | 21 mbps
45-50mins - 1 hr 30 mins - 3 hrs
PH 720 60p, 30p, 24p 21 mbps |
45-50mins - 1 hr 30 mins - 3 hrs
heres a storage chart
HE 1440x1080 60i | 6mbps
3 hrs (8gb)- 6 hrs(16gb) - 12hrs(32gb)
HG 1920 x 1080 60i | 13mbps
1hr 15 mins- 2 hrs 30 mins- 5hrs 15mins
HA 1920 x 1080 60i | 17mbps
1 hr - 2 hrs - 4hrs
PH 1920x1080 60i, 30p, 24p | 21 mbps
45-50mins - 1 hr 30 mins - 3 hrs
PH 720 60p, 30p, 24p 21 mbps |
45-50mins - 1 hr 30 mins - 3 hrs
Last edited:
ullanta
Veteran
The second one is easy - eight bits/byte means that 1MB/s = 8Mb/s
The first question is more complicated for a number of reasons. First, there are two standard definitions for the common terms megabyte and gigabyte. People who sell hardware like to describe a megabyte as 1 million bytes, and a gigabyte as 1 billion bytes. Most software/operating systems consider a megabyte to be 2^20 (1,048,576) bytes, and a gigabyte to be 2^30 (1,073,741,824) bytes. That's one of the reasons why an 80GB hard drive only holds 74 GB or so.
Second, the HMC uses variable bitrate encodings, though in my experience they tend to hold the average well.
So, assuming you're shooting PH mode, 21Mb/s = 2.86 MB/s, or 157.5 MB/minute, or 9450 MB/hour, or about 9.23 GB/hour.
This plays out for me in the real world... using Transcend 16GB SDHC cards (which are really 15GB or so), I get about 99 minutes in PH mode, 130 minutes in HA, 165 minutes in HG.
Does that answer your question?
The first question is more complicated for a number of reasons. First, there are two standard definitions for the common terms megabyte and gigabyte. People who sell hardware like to describe a megabyte as 1 million bytes, and a gigabyte as 1 billion bytes. Most software/operating systems consider a megabyte to be 2^20 (1,048,576) bytes, and a gigabyte to be 2^30 (1,073,741,824) bytes. That's one of the reasons why an 80GB hard drive only holds 74 GB or so.
Second, the HMC uses variable bitrate encodings, though in my experience they tend to hold the average well.
So, assuming you're shooting PH mode, 21Mb/s = 2.86 MB/s, or 157.5 MB/minute, or 9450 MB/hour, or about 9.23 GB/hour.
This plays out for me in the real world... using Transcend 16GB SDHC cards (which are really 15GB or so), I get about 99 minutes in PH mode, 130 minutes in HA, 165 minutes in HG.
Does that answer your question?
Allen Ellis
Well-known member
This is a great explanation - just to elaborate on it a little...
The reason GB is really measured as 2^30 instead of simply a billion bytes is because a lot of times in computer hardware a power of two is required. This is why memory cards go from 1GB to 2GB, then 4GB, then 8GB, then 16GB, then 32GB - they keep doubling.
This exact same formula is taking place at the microscopic byte level, too. And the closest number to a thousand in that chain happens to be 1,024.
(The powers of two go: 1 - 2 - 4 - 8 - 16 - 32 - 64 - 128 - 256 - 512 - 1024)
So a kilobyte (KB, with a capital B) = 1,024 bytes
A megabyte (MB, capital B) = 1,024 kilobytes
A gigabyte (GB, capital B) = 1,024 megabytes
It can seem like an insignificant difference - after all, who cares about that extra '24', right?
But if you wrongly substitute in 1,000 as all hard drive manufacturers do (cheating IMO), the errors really add up.
A terabyte should, by definition, consist of 1 099 511 627 776 bytes. But if you buy a so-called "1TB hard drive" today you'll only get 1 000 000 000 000 bytes. That's because the critical '24' has been left out billions of times, adding up to a loss of 91GB.
This all comes back to reality as ullanta said it if you want to calculate exact record times. If you forget to take this into account your calculations are going to be off by about 6 or 7%.
ullanta
Veteran
For all the good the calculation will do, though, given all the variables, the best thing to do is insert a blank card and switch modes... while knowing the basic math and doing some calculation is certainly useful, the most useful part of what I wrote, I think, are the real-world results:
mcsmooth
Well-known member
I did some similar math recently but was checking to see what real word results I was getting from full cards. My 16GB cards are also roughly 15GB. PH mode averages out to 100 minutes, so that is 150MB/minute or 9GB/hour. Those are easier rough numbers to work with, but actual values were usually a tad higher, like above. Because of variable bitrates and drive/card capacities, theres little use trying to esitmate more accurately like you can with a streaming format (eg. DV, HDV, or DVCPROHD). Figure you can get about 100 minutes on a "16GB" card and 100 hours on a 1TB drive (which are really ~930GB).
Yes, annoying, but at least it is a consistent marketing standard that is to be expected. It cracks me up all the reviews people make about any type of storage complaining about the missing space, blaming it on that specific product or their OS. I'm pretty sure the 1000 bytes disclaimer is always in the fine print these days. Well, at least we'll always get the extra bytes with our RAM
Another side note, I have 2 16GB cards from the same manufacturer that look the same, but have slightly different capacities. I only noticed this when trying to transfer contents back to the smaller one (to play back on the camera) and it did not have the space. Not really an issue for anything else.