[László Kovács] “Well, looking at DVDA 7.0 I feel I would like to get ac3 pro back.”
Short answer from user Cornico on the MAGIX Vegas forum:
1. Copy the file ac3plug.dll from your C:\Program Files\Sony\Vegas Pro 13.0\FileIO Plug-Ins\ac3plug
2. Rename it to ac3studioplug.dll
3. Change this file with the ac3studioplug.dll from your C:\Program Files\VEGAS\VEGAS Pro 14.0\FileIO PlugIns\ac3studioplug.
Long answer is this thread where the fix came from. The post from Cornico is at the top of page 3.
AC3 pro render missing in VP14