Trancode only audio from mkv

Hello,
how have to look a profil in the profile file, when i just want to trancode the audio stream from a mkv file from dts to ac3 or stereo?
Greetings
how have to look a profil in the profile file, when i just want to trancode the audio stream from a mkv file from dts to ac3 or stereo?
Greetings