Compresses a video using ffmpeg for conference submissions

compress_video

# First, resize the video to a reasonable size. Here only the width is specified, and the height is determined by the 
# aspect ratio.
ffmpeg -i input.mp4 -vf scale=1024:-2 -an input_resized.mp4

# Here a bitrate of 300k is used. To calculate the right bitrate, use the formula:
# bitrate = FILE_SIZE*8192*1000/LENGTH
# where FILE_SIZE is in MB and LENGTH is in seconds, and the output bitrate is in kilobits.
# e.g. for a 137s video and a desired file size of 5MB, the bitrate should be around 5*8192*1000/137 ~ 300k
ffmpeg -y -i input_resized.mp4 -c:v libx264 -preset medium -b:v 300k -pass 1 -an -f mp4 /dev/null
ffmpeg -i input_resized.mp4 -c:v libx264 -preset medium -b:v 300k -pass 2 -an input_compressed.mp4

You might get better results using the -crf option, but this guarantees the output file size.