who know what s/w is use to convert to rm file to mpeg file one??

when i use the TMPGEnc Plus to convert my rm file some of the file that i convert just have the video but no sound. why this will happen one??

ty for helping but now i using the ImToo Rm converter. it quite ok to make the rm to mpeg2 because i wanna make the file that i dl can be watch by the dvd player.