These commands require FFmpeg and ImageMagick, available for both Windows and Linux.
Convert an AVI to MP4
ffmpeg -i input.avi -c:v libx264 -crf 19 -preset slow -c:a aac -b:a 192k -ac 2 out.mp4
Auto orient, resize and change quality of an image
convert -auto-orient input.jpg -resize 2048 -quality 80 output.jpg
Convert a series of images into a video
ffmpeg -pattern_type glob -i 'cam*.jpg' -c:v libx264 out.mp4