Ho fatto una piccola ricerca ...
Questi sono i formati supportati da YouTube:
Supported YouTube formats YouTube supports a wide variety of the range of video and audio formats in use. You can get a quick overview of what may be an issue with your video`s formatting by taking a look at the warnings and error messages that we communicate to you while you`re uploading your video.
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
.WMV
.FLV - Adobe-FLV1 video codec, MP3 audio
Per essere compatibile con i Mobile Device tipo iPHONE devi caricare un video codificato in H.264
H.264 non è un codec incluso in Microsoft Movie Maker quindi lo devi convertire.
Ti ho trovato un software free che converte il formato WMM (Windows Movie Maker) in H264
www.erightsoft.com/SUPER.htmlAlla fine devi solo convertire il tuo video WMM in un H264 con estensione .MPEG4 o .MOV e ricaricarlo su YouTube
Buon lavoro