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.
“One Peg More” Video:
Standard Version (320×240)
MP4 Version HQ (480×360, H.264, AAC)
Non-MP4 Version HQ (448×336, 44,100 Hz)
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.
UPDATE: I have noticed that more videos work with the MP4 version trick. And it also seems that despite being higher quality these videos are still in mono not stereo sound.
UPDATE 2: YouTube has added a “Video Playback Quality” option in “My Account” settings. From here you can choose to “always play higher-quality video when it’s available”.
Sources: InsideGoogle | CyberNetNews | VideoHelp Forum
Amarjeet Rai's Blog 
wow, cool. About time too.
Have a look at my blog, it’s all about the stories behind viral/youtube videos:
http://downthetube.wordpress.com/
even though YouTube is displaying high quality videos, there are about 20%. But still you need to know why might not be to have hi res videos in YouTube yet as I read in this article called YouTube high definition:
http://www.squidoo.com/youtubehd
JUST A THANKS FOR USEING MY VIDEO AS AN EXAMPLE:)
MUCH APPRECIATED..
GOP VIRK
lol
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