You probably want something like this
http://www.videohelp.com/tools/SUPER
Tool features, Convert:
3GP to 3GP , 3GP to AVC , 3GP to AVI , 3GP to DivX , 3GP to FLV , 3GP to H264 , 3GP to MP4 , 3GP to MPG , 3GP to XviD , ASF to 3GP , ASF to AVC , ASF to DivX , ASF to FLV , ASF to H264 , ASF to MP4 , ASF to MPG , ASF to XviD , AVC to AVC , AVC to AVI , AVC to DivX , AVC to FLV , AVC to H264 , AVC to MP4 , AVC to MPG , AVC to XviD , AVI to 3GP , AVI to AVC , AVI to AVI , AVI to FLV , AVI to H264 , AVI to MP4 , AVI to MPG , AVI to XviD , DivX to 3GP , DivX to AVC , DivX to AVI , DivX to DivX , DivX to FLV , DivX to H264 , DivX to MP4 , DivX to MPG , DivX to XviD , DVB to AVI , DVB to DivX , DVB to DVD , DVB to FLV , DVB to XviD , FLV to 3GP , FLV to AVI , FLV to DivX , FLV to DVD , FLV to H264 , FLV to MP4 , FLV to MPG , FLV to VOB , FLV to XviD , H264 to 3GP , H264 to AVC , H264 to AVI , H264 to DivX , H264 to FLV , H264 to H264 , H264 to MP4 , H264 to MPG , H264 to WMV , HDTV to AVI , HDTV to DivX , HDTV to DVD , HDTV to FLV , HDTV to H264 , HDTV to MP4 , HDTV to MPG , HDTV to VOB , HDTV to XviD , MOV to 3GP , MOV to AVC , MOV to AVI , MOV to DivX , MOV to FLV , MOV to H264 , MOV to MP4 , MOV to MPG , MOV to XviD , MKV to 3GP , MKV to AVC , MKV to AVI , MKV to DivX , MKV to FLV , MKV to H264 , MKV to MP4 , MKV to MPG , MKV to XviD , MP4 to 3GP , MP4 to AVC , MP4 to AVI , MP4 to DivX , MP4 to FLV , MP4 to H264 , MP4 to MP4 , MP4 to MPG , MP4 to XviD , MPG to 3GP , MPG to AVC , MPG to AVI , MPG to DivX , MPG to FLV , MPG to H264 , MPG to MP4 , MPG to MPG , MPG to XviD , OGM to 3GP , OGM to AVC , OGM to AVI , OGM to DivX , OGM to FLV , OGM to H264 , OGM to MP4 , OGM to MPG , OGM to XviD , RM to 3GP , RM to AVI , RM to DivX , RM to FLV , RM to H264 , RM to MP4 , RM to MPG , RM to XviD , VOB to 3GP , VOB to AVI , VOB to DivX , VOB to FLV , VOB to H264 , VOB to MP4 , VOB to MPG , VOB to XviD , SWF to 3GP , SWF to AVC , SWF to AVI , SWF to DivX , SWF to FLV , SWF to MP4 , SWF to MPG , SWF to XviD , WMV to 3GP , WMV to AVI , WMV to DivX , WMV to FLV , WMV to H264 , WMV to MP4 , WMV to MPG , WMV to XviD , XviD to 3GP , XviD to AVI , XviD to DivX , XviD to FLV , XviD to H264 , XviD to MP4 , XviD to MPG , XviD to XviD