The most reliable way to ensure a desired length for an output is to specify -t X on the output.
But if you need adaptive limiting of the output duration, use
ffmpeg -loop 1 -framerate 5 -i 000.png -i 000.wav -c:v libx264 -c:a aac -b:a 192k -shortest -fflags +shortest -max_interleave_delta 500M out.mp4
The fflag is applied deeper in the processing pipeline and should be used in conjunction with the -shortest switch. The max_interleave_delta with a high value is set to avoid writing packets already queued for output.
