Disclaimer: I’m not a video expert, so this tutorial may be entirely wrong. It reflects only my understanding of what I’ve learned so far about editing video files.
Note: I had intended to write a series of tutorials while I dealt with some menial task for a video project, but those tasks turned out to be easier than expected. So I’m not sure how many more of these entries I’ll write.
There are a lot of places on the Interwebs where you can find out about video resolutions and the first two links provided by Google are good places to start.
Assuming you can get through all the jargon that gets thrown around.
Here’s the thing you should come away with in learning about video resolution: there are many ways to describe the same thing.
Let’s begin with aspect ratio, the width of an image divided by its height. Long ago and far away when televisions started inching their way into American homes, film studios combated the perceived threat of the medium by expanding the size of the theater screen. As a result, films have an aspect ratio of 16:9, while TV has an aspect ratio of 4:3. That’s the simple history of aspect ratios.
Now comes the hard part.
4:3 and 16:9 can be expressed as a lot of other numbers — 0.9091, 1.2121, 1.333, 320×240, 640×480, 720×480, 1280×720, 1980×1080. By means confusing and technical, all these numbers represent the various ways video is displayed in 4:3 and 16:9, despite the fact some of these numbers don’t even express that proportion.
It has to do, in part, with scan lines.
The About.com article describes it best:
A television or recorded video image is basically made up of scan lines. Unlike film, in which the whole image is projected on a screen at once, a video image is composed of rapidly scanning lines across a screen starting at the top of the screen and moving to bottom.
Even though the image you see on the screen may be 4:3, the video resolution expresses the degree of granularity within that 4:3 aspect ratio. A 640×480 resolution has a 4:3 aspect ratio. 640 / 480 = 1.333. A 720×480 resolution also has a 4:3 aspect ratio. 720 / 480 = 1.5.
What? 1.333 is not the same as 1.5.
All right, let’s talk about standards. Different regions of the world have set specifications by which video makers and manufactures must abide. In North America, there’s NTSC. In Europe and Asia, there’s PAL. And there’s also SECAM, wherever that’s used. Each specification states how many scan lines can be used in video equipment.
That explains why the 480 doesn’t change between 640 and 720 — the specification deems it so.
What’s the deal with the 640 and 720, then?
Scan lines deal with vertical resolution, but each line contains a number of dots — that is, pixels — that get fired up anytime that scanning beam of light hits it. The more lines and the more dots you have, the sharper the picture becomes.
Throwing all these numbers around won’t mean a thing without seeing just how messing with them affects your picture. Ever hear of letterboxing? It’s those black bars that show up on the top and bottom of your screen if you try to watch a 16:9 film image on a 4:3 TV set. If you tried to watch a 4:3 image on a 16:9 screen, the black bars would show up on sides.
Try to fill the entire space with the image, and it gets distorted. The narrow picture on a widescreen gets stretched, while a wide image on a narrow screen gets squished. Take out the distortion, and the image gets clipped.
In the audio world, it’s best to cut than to boost, and that still applies to video as well. Analog images look terrible on high definition screens because of the differences in scan lines — the 480 vertical lines of an analog signal can’t possible fill all 720 lines of a hi-def screen. It’s like transcoding a 128kbps MP3 to 192kbps — it’s still going to sound like a 128kbps MP3.
So if you want to watch a video shot at 320×480 on a DVD player, you cannot help but have a fuzzy picture. And if you transcode a high definition video to standard definition — no, I’m not even going to get into what those terms mean — then try to upload to a site that supports high definition, you get a letterboxing double whammy.
Combine these concepts with the lesson about codecs, and … well crap, my brain just shut down trying to keep all of it together.
And there’s still much more to learn.