Audio stream not initializing

Okay I’m trying to finish up my animation by rendering it from pngs to an mpeg, but when i do so an error comes up saying cannot initialize audio stream. I’m using mp3 with 256 bit rate. I don’t know why it is doing this but it is starting to become quite annoying see as how any other codec it just changes the sound into a high pitched ring. is there anyway to fix this, or a good codec setup for 1280x720 animation.