As I am participating in BOFU2015, our team made BGAs in 1080p HD format, but to use them in LR2, we need to convert them to MPEG with 1:1 aspect ratio first.

For that, we first crop the video to 4:3 aspect ratio, then add letterbox.

We need to do both cropping and letterboxing, because otherwise, either the video is too small, or many surrounding details will be removed.

Here is the ffmpeg command I used:

ffmpeg -i "$1" -filter:v "scale=853x480, crop=640:480:107:0, pad=640:640:0:80" -pass 1 -f mpeg1video -b:v 2048k -an -passlogfile log_file -y "$1.mpeg"
ffmpeg -i "$1" -filter:v "scale=853x480, crop=640:480:107:0, pad=640:640:0:80" -pass 2 -f mpeg1video -b:v 2048k -an -passlogfile log_file -y "$1.mpeg"

512x512 version

ffmpeg -i "$1" -filter:v "scale=683x384, crop=512:384:86:0, pad=512:512:0:64" -pass 1 -f mpeg1video -b:v 2048k -an -passlogfile log_file -y "$1.mpeg"
ffmpeg -i "$1" -filter:v "scale=683x384, crop=512:384:86:0, pad=512:512:0:64" -pass 2 -f mpeg1video -b:v 2048k -an -passlogfile log_file -y "$1.mpeg"