How to make a video from a still image and an audio file?
To expand upon ObscureRobot's answer, use ffmpeg like so:

ffmpeg -loop 1 -f image2 -r 2 -i input1.png -i input2.aiff -c:v libx264 -c:a copy -shortest output.mp4


-loop 1 -f image2 -r 2 -i input1.png tells ffmpeg to loop input1.png forever, at a frame rate of 2fps. -c:v libx264 tells it to use x264 to encode the video, and -c:a copy tells it to simply copy the audio, without encoding. -shortest makes ffmpeg stop when the shortest input ends - input2.aiff in this case.