I wanted to reuse the work around previously suggested by Graham to convert an AC3 file to another audio codec.
I followed this proceed sometime back & it worked just fine.
I tried it again the other day & have problems. I set DVDA back to a DVD project & dragged the AC3 file onto blue background. The file size was 180 MB. I clicked make DVD then prepare & told the program to save it to desktop. When I opened the Video_ts file in Vegas & dragged the vob file to the timeline the clip was only 5 seconds long.
I went back to the DVDA which was still open & clinked on Optimize disk looked at the tabs & saw that the duration was set to 5 seconds for video. How do I get it to match the duration of the audio?
I personally convert AC3 to WAV (though I rarely do this nowadays) before going to another format. You can use free software (like eac3to) to process the audio and it is rather quick.
To attempt to answer your DVDA question, it sounds like you are dragging it on to a menu. Under the general tab when the menu is opened, make sure that the length is set to the the length of the audio (usually auto calculate does this however).
Perhaps post a screenshot though and it will be easier for people to see what you are doing and provide better help.