Ffmpeg: need for speed
===

I am using ffmpeg to convert a set of images (bmps) with an audio track into Web ready video. Target formats are h.264 mp4, webm and flv. 
This is on a Windows Azure extra-large instance (8 proc) using the prebuilt zeranoe static builds ( http://ffmpeg.zeranoe.com/builds/). 

Suppose I'm willing to sacrifice quality and size for raw speed. What options for each format will yield the quickest result? 

My "baseline" command looks like this: 

    ffmpeg -y -i frames%5d.bmp -i audio.mp3 -r 23.97 out.mp4

I can change the inputs to other formats if needed (jpg images, aac audio, etc). 