Freesound Forums

I have created a game that uses some sounds licensed under CC BY 3.0 from freesound. These sounds are fully attributed in the credits of the game.

There is also a trailer on youtube that uses recorded game footage that happens to contain some of these sounds. I included credits in the description, but are they absolutely necessary in this case? If they are needed, how should I go about adding attribution to the trailer if it's hosted somewhere that has no description to include these credits?

I've tried contacting the creators and I haven't heard back. I also can't add full credits to a trailer. Would a small disclaimer at the end of the video with a text url pointing to the credits list possibly be sufficient?

In your case, attribution using a method of redirection in an accessible place would suffice.
According to creative commons, if you state the author/title and produce a link to the source somewhere in conjunction to the media you are presenting, that is okay. But according to them you should also state the license type (but that isn't absolutely necessary in my view)

This is an ideal attribution:

"audio file name [link]" by username [link] is licensed under CC BY 2.0

The order for the above credit string can be different, doesn't matter really as long as you state the author name/filename and provide a link you'll be fine. Check out the link I provided above named "source" for broader information on the topic from Creative Commons.