Here is a list of some well-known formats that YouTube supports:
WebM files – Vp8 video codec and Vorbis Audio codecs
.MPEG4, 3GPP and MOV files – Typically supporting h264, mpeg4 video codecs, and AAC audio codec
.AVI – Many cameras output this format – typically the video codec is MJPEG and audio is PCM
.MPEGPS – Typically supporting MPEG2 video codec and MP2 audio
.FLV – Adobe-FLV1 video codec, MP3 audio
Here is a list of some common formats that YouTube does NOT support:
Project files: No project files of any kind are acceptable. It is generally very easy to convert project files to a supported format.
MSWMM and WLMP: You can easily convert these project files to .WMV.
Audio files (MP3, WAV, etc.) and Image files (JPG, PNG, etc.)