ffmpeg(1) -framerate 3 -pattern_type glob -i '*.jpg' -vf "scale=iw*min($width/iw\,$height/ih):ih*min($width/iw\,$height/ih), pad=$width:$height:($width-iw*min($width/iw\,$height/ih))/2:($height-ih*min($width/iw\,$height/ih))/2" video.mp4
ffmpeg video converter
-r fps
    Set frame rate (Hz value, fraction or abbreviation), (default = 25).
-t duration
    Restrict the transcoded/captured video sequence to the duration specified in seconds.
    "hh:mm:ss[.xxx]" syntax is also supported.
-y  Overwrite output files.
-i filename
    input file name
    -vf filter_graph
        filter_graph is a description of the filter graph to apply to the input video.  Use the option
        "-filters" to show all the available filters (including also sources and sinks).

Advanced Video Options
    -pix_fmt format
        Set pixel format. Use 'list' as parameter to show all the supported pixel formats.
source manpages: ffmpeg