Audio Permission

Loss; Composed by Enrico Altavilla, freesoundtrackmusic.com

I have not purchased any download credits. If I use one of the tracks from your site in my video, do I have to put "freesoundtrackmusic.com" in the actual video somewhere? 

No. Many small productions (like Youtube videos) will not have a credits section. In these cases, a small mention in any of the descriptive text (either online or printed) accompanying the video will be sufficient. Alternately, purchasing a single download credit (for only $3.50 USD) entitles you to use either "FREE" or "1 credit" tracks in your productions without any mention of freesoundtrackmusic.com.

Black Vortex;  Composed by Kevin McLeod, incomptech.com

By default, they are licensed under Creative Commons: By Attribution 3.0. To use this license, simply attribute the music in your piece (website, film, phone system, etc.) as is reasonable to the medium.
There is no cost to use music under the Creative Commons License.

Step 1: Give Credit

Short example:
Title Kevin MacLeod (incompetech.com)

If you'd like to include the full license for legal reasons, you can do the following:

Title Kevin MacLeod (incompetech.com) 

Licensed under Creative Commons: By Attribution 3.0
http://creativecommons.org/licenses/by/3.0/
It is important that you replace the word Title with the Actual Title of the piece that you are using!