I'm following this page: Creating Timelapse Videos With The Raspberry Pi Camera.
But every time I try to make the video, I get this error:

original: https://i.stack.imgur.com/ApIJ0.png
Specifically this command from the output above:
$ avconv -r 10 -i pic_%04d.png -r 10 -vcodec libx264 -crf 20 -g 15 \
-vf crop=2592:1458,scale=1280:720 timelapse.mp4
...
...
Output #0, mp4, to 'timelapse.mp4':
Output file #0 does not contain any stream
Also when using mencoder, following this page: 6.8. Encoding from multiple input image files (JPEG, PNG, TGA, etc.):

original: https://i.stack.imgur.com/svNLx.png
Can someone please help?