One of the most common questions that people have when they first start to conceive content for Youtube is Which file format does Youtube support? What file format should I use when I upload to Youtube?
Luckily, it accepts a pretty wide variety. Looks look at the more popular ones first.
This is a file format found in a lot of cameras, and is preferred by Mac computers. There's a pretty good chance that your camera or video editing software will use this format as a default, or that you'll be able to export to this format very easily.
.AVI files are rampant. If your camera doesn't use MOV, it probably uses AVI. AVI is a default format for tons of video editing software, and an AVI file can range from uncompressed (huge files) to fairly small compressed files (usually with the MJPEG codec which is very common, and Youtube supports it).
If you're working in a Windows environment, particularly if you're editing in Windows Movie Maker, this is the format of choice. It produces very small files of fairly good quality, and it's perfect for Youtube.
Large files and high quality video, this common file format/codec is available in many cameras. If this is the format you're working in, no worries -- Youtube accepts it!
Adobe's FLV codec is out there and has been gaining steam for years ... and Youtube supports it!
The Vorbis Audio and Vp8 video codecs are also supported.