I always use this Video Converter. It supports the mutual conversion between almost all video/audio formats, and HD videos.
Input Formats: MPG, MPEG, MPEG 2, VOB, DAT, MP4, M4V, TS, RM, RMVB, WMV, ASF, MKV, AVI, 3GP, 3G2, FLV, SWF, MPV, MOD, TOD, QT, MOV, DV, DIF, MJPG, MJPEG
Output Formats: MP4, H.264, AVI, MP3, WMV, WMA, FLV, MKV, MPEG-1, MPEG-2, 3GP, 3GPP, VOB, DivX, Mov, RM, RMVB, M4A, AAC, WAV, OGG, RA.
It also can set video effect, set Deinterlacing, trim your video length, crop the play region, merge into one file, customize output settings.
For more informaion and free download from:
http://www.google.com/search?hl=en&q=tipard++video+converter&aq=f&aqi=&aql=&oq=&gs_rfai=