This is a question that comes up when people are new to working with video. Video cameras and displays are so ubiquitous now, that it’s easy to be unaware of the technical challenges video poses. Warning! There will be math involved 🙂
Let’s begin with a statement I make at the beginning of video editing courses. When we watch a movie or a TV program, nothing on the screen moves. “But wait!” you might ask. “I just saw Lassie run up to Timmy!” What you saw was an illusion. Motion pictures, as we like to refer to motion picture film and video, do not move. Instead, a series of images is flashed in front of our eyes at a fast enough pace to cause our brains to interpret what we see as motion. Luckily, we don’t need to know this little secret to enjoy a great movie – in fact it’s best to forget in order to become immersed in the story. However, this allows us to begin to understand a few things about handling video.
Motion pictures are actually a stream of individual images displayed in order at a relatively fast rate. We call the individual images frames. A frame is a single image out of the group. I the digital realm, images are a 2-dimensional grid of picture elements – aka pixels! A pixel contains just enough information to define a color – typically three bytes Don’t worry if you don’t know what a byte is – just know that it’s a small bit of digital data, and our foundation for measuring file sizes.
There are many frame sizes in use – we’ll use an HD video standard as our example today. A full HD frame is 1920 pixels wide and 1080 pixels tall. From that, we can determine the size of an individual frame of HD video: 1920 x 1080 x 3 = 6,220,800. Roughly, 6 million bytes, or 6 megabytes (MB). Not huge by today’s computer file standards, but remember – this is one frame out of many. How many?
Enter our next piece of the equation. The next way that we measure moving pictures is by frame rate. How fast are those frames flashing in front of our eyes? There are many frame rates in use, depending on the technology. Many cartoons run at 12 frames per second (fps) – just fast enough to create the illusion. This is important to animators, as drawing or rendering individual frames can be time-consuming. However, 12 fps is not very smooth. Film usually runs at twice that amount: 24 fps. Video in the US and most of North America runs at 30 fps (OK its really 29.97 fps, but close enough!), including HD video. Let’s do the math…
6MB frames x 30 fps = 180MB per second
180MB per second x 60 = 10,800MB per minute – approx. 10 gigabytes (GB)
10GB per minute x 60 = 600GB per hour – yikes!
Even with today’s inexpensive hard drives, it can cost a lot to store much video in it’s uncompressed form, and will take huge amounts of time uploading to a website. Luckily, there are groups of incredibly smart people out there figuring out ways to shrink our video files to more manageable sizes. Using a variety of compression techniques, we get high quality motion pictures to upload more quickly and to fit onto USB drives, etc.
There are many more varieties and flavors of video tech than can be covered in a blog page. The main perspective to take away is that video files are gigantic compared to most other computer files. Be patient when it takes an hour to export your 15 minute masterpiece and another hour to upload it to YouTube 🙂
In the next post, I’ll teach you how web color codes work – in other words: I call it red, but my website calls it ff0000?!?