First of all, I would highly recommend you to update ffmpeg to a newer version. You are currently using v1.2.6-7, but as we speak, the current version is 2.3.3.
Here is a working command (see ffmpeg wiki):
ffmpeg -loop 1 -i image.jpg -i audio.mp3 -c:a copy -c:v libx264 -shortest out.mp4
Also, you could optimize overall weight by reencoding audio if you’re using raw sound (aiff or wave) as input:
ffmpeg -loop 1 -i image.jpg -i audio.wav -c:a aac -ab 112k -c:v libx264 -shortest -strict -2 out.mp4
For further reading, see this related stackoverflow post.