YouTube has started making available higher resolution versions of its videos, offering 480×360 video with higher quality audio, up from the standard resolution of 320×240. The video is MP4 with AAC audio. It has also made available 448×336 video, with 44100 Hz audio, double the normal.
To benefit from this, append &fmt=18 to the end of a video URL to get 480×360 video with higher quality audio. Or append &fmt=6 and get 448×336 video, with 44100 Hz audio. However, not all videos will work. Newer ones are most likely to work, as the source file is there so it can be converted.
One video I did notice that does have the higher quality video is the “One Peg More” video by Gop Virk & Laddi Bath.
If you are embedding the videos and want the higher quality version, add “&ap=%2526fmt%3D18” after the video URL in both places in the embed code (or “&ap=%2526fmt%3D6” for the non-MP4 high quality version).
You can also download these videos using KeepVid appending the code at the end of the download URL. I downloaded all three versions, the standard version is 8.59 MB, the MP4 version is 16.4 MB and the non-MP4 high quality version is 24 MB, the largest of the lot.
From looking at just this example, I noticed that the non-MP4 high quality version has got clearer images than the MP4 version, despite it having a higher resolution, but this may not be true for all videos. It could be because I was using QuickTime to view the MP4, and YouTube for the others. I could be wrong. Try it out, and tell me what you think.