1.Set default factory settings for Sony vegas pro 11 or 12 or 13 [ any version]
Click on start on your windows -> programs -> Press & Hold CTRL+SHIFT while clicking on the Sony vegas pro icon .You must continue to hold the CTRL & SHIFT keys .Now a pop-up show message " DO you want to allow this app..." Click on "Yes" .NOw another pop-up Show message"Doyou want to reset all vegsa pro preference to default values .Select the checkbox next to “Delete all cached application data” and then click Yes.
Strech or compress the length of the video
Press Ctrl Key + Mouse | Stretch or compress the length of the video by use the mouse at the end of the clip
2.Seperate Audio from Video
Select the audio track and press " ctrl + u " the audio will be seperated from video. Now you can delete the audio
3. Add new audio track to the video and merge them
After doing the step 2. you can add new music or voice-over to the video and merge them
Hold the "Ctrl" key and select the video and audio track and release the "ctrl" key and press "G" key.
Now the audio and video is merged.