convert images to a video (Ubuntu)

use =avconv= package

 e.g.  to convert images (v_1.png, v_2.png ...) to 'velocity.mp4'

              >>> avconv -i v_%d.png -b:v 1000k velocity.mp4

- i :: input file
- b :: bitrate

References:

https://stackoverflow.com/questions/16315192/avconv-make-a-video-from-a-subset-on-images

https://libav.org/avconv.html