Why are some YouTube videos so much better quality than others? What video specs and file format (AVI, MOV, MPG) produce the best results?

YouTube video probably varies in quality a great deal because of the source material. Probably a lot of stuff there that's been passed around for years, and degraded as its been converted from one format to another. And then there is probably crummy mobile phone video. YouTube looks like it converts everything to flash video format with a max resolution of 320x240. Furthermore, source files are limited to 10 minutes and 100MB. To get the best conversion, you'd want to start with a high quality source, match that resolution, and maximize the filesize while using the most efficient codec available, which is probably h.264 at that bitrate range. I wonder if they'll accept flash video without trancoding it as long as it fits the parameters for resolution, bitrate and other parameters.

I've tried mpeg and they came out pretty crappy. What happens is it re-encodes the files to .flv and a lot of the videos have already been compressed once or even twice. In my case I think they were compressed, captured from TV and recompressed and then recompressed when they were converted to youtube. In my experience any video codec will start to look like crap after the say forth compression (like duping tapes, etc). If you wanted to highest quality use the latest codecs they can handle (mp4?) and compress it to the highest amount under 100 megs and make sure it was compressed from an original uncompressed format. Usually can get away with two recompressions. Also certain things look better such as lower frame rates (certain types of animation with little movement), less black and green colors, less motion on the screen, less difference in color.

http://www.youtube.com/watch?v=kx4d33Q43bA was a first-generation 640x480 motion-JPEG source and it looks like crap. So I'm not sure what the solution is.

smakfu, your video is more of a problem of youtube using such a lofi amount of compression. There's a lot of motion in there (think of it as a difference between each pixel) and green/blue colors, both of which will turn out bad. Also I think your best bet is to make sure its resized to the lower resolution yourself.

YouTube's tech support finally got around to responding to my inquiry, so I'm answering my own question ;-) From their recently-updated http://youtube.com/t/help_makevideo: What's the best format to upload for high quality? We recommend the MPEG4 (Divx, Xvid) format at 320x240 resolution with MP3 audio. Resizing your video to these specifications before uploading will help your clips look better on YouTube.