For your lack of custom options, try this tip from Edward Troxel’s Vegas FAQ:
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Look in your registry, and make sure it only has these entries, and nothing else.
[HKEY_LOCAL_MACHINE\SOFTWARE\Sony Media Software\MC MPEG Plug-In\1.0\License]
“CurrentKey”=”XX-XXXXXX-XXXXXX-XXXXXX”
“InstFlags”=dword:00000010
(you shoud see letters and digits instead of the Xs here…)
If it is not “CurrentKey” or “InstFlags”, get rid of it.
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For #2, you’ll need to render the audio using the AC-3 template. As long as you put it in the same folder as the mpeg-2 file, DVDA will automatically load the audio as soon as you select the video stream.