I'm pretty sure that YouTube will allow you to upload an .AVI video exported from Movie Maker, but from my experience the best format for getting HD (High-Definition) videos is to upload as a H264 .MOV. But don't take my word for it. Here are the official YouTube recommendations:
QUOTE:
Video:
Format - MP4 codec, (not xvid)
Frame Rate - 25fps
Decoder - H.264,
Resolution - 1280x720,
Bit Rate - 1411kbps average; but varies according to what you upload.
A ceiling of 4028 is as high as you should ever attempt to upload.
Even that is too high for consistent performance and normally fails
with glitches n stutter on viewers browsers. The size would also be
larger with a longer upload process.
To get best YT on site transcoding, never upload videos much higher
than 2000kbps for best results. With that, YouTube will hit that
average on the mark, in conversion. That with an average on site file
size of 30 to 60mg, for an average 3-4min HD video!
Audio:
Frequency - 44,100htz (anything less or higher may not work in the any
flash player)
Codec - AAC (this is what YT uses, best if uploaded file is not the
inferior mp3 codec. As it must then be transcoded on site for HD.
Meaning upgrading data info that isn't there in mp3)
Bitrate - 128kbps
Channels - 2
Bits per sample - 16
Note: MP4a is the ffmpeg audio container and MP4v is the ffmpeg video
container.
The closer you get your HD file to these settings the more likely your
video will run properly on YouTube, once uploaded. Remember files
proportionate to their duration work best. If you are trying to upload
a 500mg 4min file, it's bound to have problems, as it's most likely in
a raw format. Any raw AVCHD file with the extension .mt2s, right out
of a camera will most likely fail!!!
The list of conversion tools available would take up a page itself.
But here's the short list:
Some Free Programs that do the job!
1. Super Converter (has some issues, but overall works great)
2. PS3Video9 (works depending on what you're converting from)
3. Any Video Converter Freeware (very good program but you will be
bugged to buy licensed version!)
4. Megui (powerful Open Source program, but not the best for a
beginner)
5. Cinelerra for Video Production and Editing (not for beginners at
all and it's Linux only) What the Pros use and there's very little
that it can't do!!!
/QUOTE