Start Sony Vegas and download the file you need. You can do this in the menu “File” -> “Open” or by opening the folder with the video in the normal “Explorer” and dragging the object icon onto the temporary table of the program. Please note that after loading, two tracks appeared on the temporary table: the top shows footage of the video, on the bottom – sound oscillations.
Click on any of the tracks, which should lead to the selection of both. At this stage, the sound and video are “linked” into a single group. You can split them by the option “ignore grouping”: it is called by a special button on the top panel (Ignore Event Grouping), the context menu command (one of the lines that appears when you click right click) and Ctrl+Shift+U. After the command is called, reset the current selection by clicking anywhere in the screen and try to drag the audio track. Now she moves regardless of the audio.
If you need to separate the sound only in part of the video, then the separated sound track must be limited. To do this, put a marker at the moment where the sound should end and press S. The audio will split into two independent pieces. Obviously, if the sound is to “come back”, then a similar cut must be made at the right moment.
To keep the sound track separate from the video (or vice versa) then, after separation remove the unnecessary component from the monk table. After that, select File – Recalculate As menu. A window similar to the Save File dialog appears: at the bottom you can select the desired output format. Obviously if you choose .mp3 then the video will not be saved. But if a video format (such as .avi) is selected to save, all the contents of the desktop will be saved: make sure that unnecessary audio tracks are not there.