Understanding how to calculate storage space required from bitrate can only affect your workflow in a positive way, as a filmmaker, or editor, it’s imperative that you understand how to calculate storage space. Let’s discuss in detail what a bitrate is and how to use it to calculate file sizes.
There will come a time when you are shooting with a new camera, and you need to know how long your memory card will last. It’s simple, and all you need to know is the bitrate of the camera’s codec and a fairly simple formula.
To make it easy, there are video file size calculators out there, but unfortunately, they don’t include every codec, and manually calculating filesize is a simple task.
Many are intimidated by all of the numbers involved in calculating video bitrates and file size, it’s really not that hard. Let’s get started.
bits versus Bytes
Here is the most important thing about calculating bitrates: bits vs Bytes. The concept is simple: 8 bits = One Byte.
It’s important to note the naming convention is to use a lowercase b for bits and an uppercase B for bytes. If you need to convert bits to Bytes, you divide by 8. For example 800 Mb‘s = 100 MB‘s. The Formula is (800 / 8 = 100).
To convert the other way, MB‘s to Mb‘s multiply by 8. For example 800 MB‘s = 6400 Mb‘s. The formula is (800 * 8 = 6400).
When someone tells you about video bitrates, they usually give you that number in megabits per second (Mbps or Mb/s). If that is the case, it’s usually easier to convert Mb/sec to MB/sec so you will work with a smaller number. It’s paramount to know if you are working with Mb‘s or MB‘s to alleviate any error.
A video bitrate is the amount of data that are conveyed or processed per unit of time. In other words, it’s the amount of information per second.
For example, let’s say we want to shoot 2 hours of footage (120 minutes) on the Epic Dragon @ 6K full format @ 24p / 8:1 which yields 89 MB/sec, we want to know how much storage space we need.
Now we need to multiply MB/sec (megabytes per second) with time [120 minutes], but we need that in terms of minutes, not seconds. So, let’s convert from MB/sec to MB/minute [MB/s to MB/m] (megabytes per minute).
89 MB/sec * 60 = 5340 MB/minute. We need to multiply by 60 because there are 60 seconds in one  minute.
Now we have MB/minute, let’s calculate the total minutes . All we do is multiply by the number of minutes we have. We shot for 2 hours, so that’s 120 minutes.
5340MB * 120 [min] = 640,800 MB total sapvce required.
Conversion to gigabytes
Ok, we have our result, but the number is HUGE. It would be easier to talk in numbers of gigabytes, not megabytes, so let’s convert to gigabytes. Simply take 640,800 and divide by 1000. (640,800 MB / 1000 = 640.8 GB)
That is it! – now we know that we need 640.8 GB‘s of space to shoot 2 hours on the Epic Dragon!
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