If you have downloaded a file from Youtube and upon playing it back discover that it has no audio,
that is likely because it HAS no audio within it.
Please open the file you downloaded in a different media player like Windows Media player/VLC or Quick Time and play it.
If it does not have audio then you have your answer.
When you use the YT Downloader found in some of our products, it finds many different video files that Youtube has created.
Some of these files are video only and contain no audio, but we can't readily determine this until they are downloaded and played.
The file you can choose reliable to have audio is the one that is marked, "best" within the list.