i am animating a short video of an aerial battle, i have aircraft flying around. when i rneder this i will get a silent video clip, in reality such an event would be very loud indeed, so my question is how do i add sound or do i need to do this with a separate program outside of blender. i notice that their are speaker objects that can be added, would i be able to parent these to the engines of the aircraft and have them emit a sound track on loop( i already have the sound as some sort of audio file), . it would be nice if i could have the sound get louder when the engines are closer to the camera, if this is possible how would i achieve it? i do not want some amazing audio track with surround sound and everything but how can i achieve this sort of thing in the way that impacts as little as possible on render times. thank you.
You can render with sound, you just have to select the right codec. I believe you can also key frame the volume. But I would suggest (for no other reason than I have not had good luck with sound and blender) using an external program. There are quite a few good free NLEs for windows and linux. Not so much for Mac.
You need to enable an audio codec for muxing the sound with the video you render. If you use an older version of Blender (like 2.65 official release) then you must use mp3, the other codecs are broken from memory. But a recent commit to trunk has fixed this.
Check out the blog in my sig below for more tips on using the VSE and manipulating audio.
Everything is keyframable in Blender and this holds for sound strips. You can animate volume, pitch, and pan so it’s very easy to achieve the effect you want in the graph editor (i.e. turn the volume up when ship approaches the camera etc).
Other than cutting a sound strip, however, and changing parameters like volume, there’s not much else you can do in terms of sound processing. You’ll need to export the audio and process it through another app (say Audacity) and then re-import it back to Blender.
Everything is keyframable in Blender
BOINGGG!!
Not really true. For instance you can not keyframe the target of a constraint or any field that is a string of characters. And sadly, you can not keyframe the count of a particle system. What are we living in, the 20th centrury?
Gee, Atom, thanx for pointing this out man! 
Allow me to rephrase then: everything is keyframable minus contraint targets & particle system count.
How’s that?