# convert M4V to MP4
ffmpeg -i input.m4v out.mp4

# convert M4V to WEBM
ffmpeg -i input.m4v output.webm

Changing Constant Rate Factor will reduce video size. Try values between 18 and 24

ffmpeg -i input.mp4 -vcodec libx264 -crf 20 output.mp4

16:40 = 1000 seconds
        1000 * 1000 = 1000000

ffmpeg -i input.mp4 -b 1000000 output.mp4

Sources

• How can I reduce a video's size with ffmpeg?