Have you every wondered what the difference is between a bit and a byte or tried to understand the meaning of a kilobyte, megabyte or a gigabyte? Understanding each of these will help you understand video bitrates and video bandwidth which are relevant to anyone using any of the available video hosting providers including iPlayerHD.
What is a bit? Is the basic unit of information used in computing. A bit is one unit. One apple on an apple tree is one unit. It's that simple. And a byte? A byte is eight apples on that same tree.
A kilobyte is a unit of information of computer storage equal to about one thousand bytes. That's one thousand times one byte. Simple math.
A megabyte is a unit of information of computer storage equal to about one million bytes. That's one thousand times a kilobyte. After all, one thousand times one thousand equals a million, right?
A gigabyte is a unit of information or computer storage meaning approximately one billion bytes. That's one thousand times a megabyte. After all, one thousand times one million equals a billion, right?
When we measure the file size of a video, we use bytes. Specifically, the amounts of data downloaded and thus the bandwidth used (they are the same thing), we measure in kilobytes (KB), megabytes (MB) and gigabytes (GB). We would say that a file that is 45 megabytes is 45 MB. We would not say 45,000 KB even though it is equal to 45 MB. We say 2 GB but we don't say 2000 MB even though they are equal. Get it?
So where file sizes are measured in bytes, video delivery is measured in bits delivered every second.
Let's talk about the speed of a video, also known as bitrate (not byterare). The higher the bitrate, the higher the quality. Bitrate is measured in bits per second. We can use either kilobits (kbits/sec or kbps) or megbits (mbits/sec or mbps). At iPlayerHD, we use kbps when we describe best-practice compression settings.
Converting is simple. A 6.3 mbps video bitrate equals 6300 kbps. At iPlayerHD, we deliver our HD videos at either 1000 kbps or 2000 kbps or a smartphone/tablet mobile bitrate under 1000 kbps. Which file we deliver depends upon the device speed or bandwidth we detect when the play button is clicked. If the bandwidth is more than 2000 kbps - the exact number is part of our secret recipe - then we deliver the 2000 kbps version.
Determining the file size of a video is based on three criteria - bitrate, length of video and the calculus. The calculas is complicated and would waste useful space here and in our heads so we'll skip it. At iPlayerHD, we've created an easy to use bandwidth and file size calculator and you can get it here.
In the calculator, change the minutes and video and audio bitrates and we'll give you the approximate file size of the video. While we've based the calculation on the H264 codec at 1280 x 720, if your video has a larger or smaller resolution, the file size will be about the same.
I hope this information is useful to you. If it is, please comment below. I'd like to know your thoughts.
Cheers.
Wes
wes@iplayerhd.com
www.iplayerhd.com
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