Hello, first of all, sorry for my English.
So, i’m gonna explain exactly what i need to do, i’ve been searching for some info but i can’t find any.
My friends and i play Battlefield 4 while we are on Skype so we can communicate better. What i need to do is to record the audio from Battlefield 4 and ONLY Battlefield 4, not the Skype conversation. I know how to record the output audio from my PC, but not from one specific progam only.
Is there any way to do it? thanks!
Not with Audacity on Windows.
Audacity records directly from the computer sound system, but the Windows sound system does not provide any means to record from one application and not another.
You could have a look at programs that are specifically designed for recording games, such as Fraps, Movavi or similar and see if they are able to do it.
Thank you so much 
The problem with this thing is Windows recognize BF4 audio as “system sound”, so, if i want to record it, it records all audios from the PC, i don’t know why 
The Windows sound system does not support routing audio signals between applications.
Some professional/semi-professional audio production programs support “ReWire” which is a closed source (proprietary) technology designed for doing so, but it is very unlikely that your game (or any game) supports ReWire. Audacity is probably not allowed to support Rewire due to license restrictions. (ReWire (software protocol) - Wikipedia)
Definitely, Rewire licensing is incompatible with Audacity:
http://wiki.audacityteam.org/wiki/Features_We_Can't_Implement#Licensing_restrictions .
You should be able to record from just one application to Audacity using “virtual cable” technology. The original Virtual Audio Cable program that does this is not free, but VB-Cable from http://vb-audio.pagesperso-orange.fr/Cable/index.htm ought to do what you want.
Gale