Explanation: Video Aspect Ratio, Definition, Upscaling and File Sizes (Read Description)

Where annotations once were:
2:23 Update: Youtube actually likes 854x480.
3:37 Youtube also added 144p = 192 x 144 = Very Low Quality Fullscreen
6:13 To clarify: Upscaling won't always make video blurry, but it certainly won't increase the quality. All it does is multiply pixels to fill in spaces needed to increase it's resolution. Which can sometimes look a bit muddy.
7:09 Uhhh, I decided against it because Camstudio messed up their quality so you couldn't tell. as I said here, test it yourself to see for fun.

A few comments asking why I don't make videos in HD spawned this video. I wanted to make this one for a while to explain what all the numbers are and what aspect ratios are. It's actually really simple because it all comes down to the resolution.

Note that upscaling from a lower resolution to a higher resolution will not increase quality. It will only increase file size. You can't create detail that wasn't there in the first place. down scaling works pretty well, though I don't know why you'd do it unless you want to save bandwidth.

Here's the aspect ratio calculator:
http://andrew.hedges.name/experiments/aspect_ratio/original.html

Here's the data I showed in the video for you to copy and past for yourself for your own use. Remember, these are all basic aspect ratios. There's a LOT more of them. But I stuck with these two common formats for the best examples:

Standard 16:9 Widescreen Ratio Video Formats

High Definition Widescreen
1080p = 1920 x 1080 = Full HD Widescreen
720p = 1280 x 720 = Standard HD Widescreen

Standard Definition Widescreen
480p = 854 x 480 = High Quality Widescreen
360p = 640 x 360 = Standard Quality Widescreen
240p = 427 x 240 = Low Quality Widescreen
Edit, Youtube made: 144p: 256 x 144 = Very Low Quality Widescreen

Standard 4:3 Fullscreen Ratio Video Formats:

High Definition Fullscreen
1080p = 1440 x 1080 = Full HD Fullscreen
720p = 960 x 720 = Standard HD Fullscreen

Standard Definition Fullscreen
480p = 640 x 480 = High Quality Fullscreen
360p = 480 x 360 = Standard Quality Fullscreen
240p = 360 x 240 = Low Quality Fullscreen
Edit, Youtube made: 144p: 192 x 144 = Very Low Quality Fullscreen

Enjoy and I hope this info helps! I kept it as simple as I possibly could.