How choose language stream in a mpeg2 vob ?

[DamienBEG]

After ripp a dvd, I obtain some .vob. I want convert this .vob in .avi files. I use virtualdub-mpeg2 (or virtualdubmod). For example, I have VTS_09_1.VOB, VTS_09_2.VOB and VTS_09_31.VOB, and I know that my 3 files contains audio multistreams with ac3 inside. When I open VTS_09_2.VOB and VTS_09_31.VOB, I have the choice between some AC3 item (on for each streams) before parsing the mpeg-2. When I open VTS_09_1.VOB, there is no choice and only one audio language. How can i find my correct ac3 in VTS_09_1.VOB.

Merci beaucoup