Ffmpeg

ffmpeg -i rea-11.mp4 -s 720x480 -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis -cpu-used 4 -threads 8 rea-11-480.webm
avconv -i 03-aula-06.mp4 -strict experimental -s 720x480 03-aula-06-720.mp4

extraindo trecho do video

ffmpeg -ss 00:00:30 -t 00:01:00 -i entrada.webm saida.webm

baixando arquivo do youtube

ffmpeg -i arquivo.flv -ab 56 -ar 22050 -b 500 -s 320x240 arquivo.mpg

avconv -i input.mp4 -s 320x240 output.mp4

ffmpeg -i input.mp4 -s 320x240 output.mp4

1920x1080 aspect ratio 16:9 => 640x480 aspect 4:3: ffmpeg -y -i import.media -aspect 16:9 scale=640x360,pad=640:480:0:60:black output.media

aspect ratio 16:9 , size width 640pixel => height 360pixel: With final output size 640x480, and pad 60pixel black image (top and bottom):

"-vf scale=640x360,pad=640:480:0:60:black"

• https://addons.mozilla.org/firefox/3590/