It's a proprietary windows format that won't play on anything else.
Video * Wide aspect ratio 16:9 (WVGA) * Video recording file format: .mp4; codec: MPEG-4 * Video recording at up to 848 × 480 pixels (WVGA) and up to 25fps * Video playback file formats: .mp4, .avi, .wmv, .3gp; codecs: H.264, MPEG-4, Xvid, WMV, H.263