ffmpeg syntax:
ffmpeg -i $SOURCE -map 0:0 -map 0:1  -vf pad="1920:1080:(ow-iw)/2:(oh-ih)/2" -target ntsc-dvd -crf 18 -ab 384k -threads 0 "$1".mpg

error i get using dvdauthor:
WARN: Discontinuity of 225 in audio channel 0; please remultiplex input.
WARN: Previous sector: 289.709 - 289.741
WARN: Current sector: 289.744 - 289.776
WARN: Audio pts for channel 0 moves backwards by 135; please remultiplex input.
WARN: Previous sector: 289.744 - 289.776
WARN: Current sector: 289.774 - 289.806
WARN: Audio pts for channel 0 moves backwards by 180; please remultiplex input.
WARN: Previous sector: 289.774 - 289.806
WARN: Current sector: 289.804 - 289.836
WARN: Discontinuity of 270 in audio channel 0; please remultiplex input.
WARN: Previous sector: 289.804 - 289.836
WARN: Current sector: 289.839 - 289.871
WARN: Audio pts for channel 0 moves backwards by 180; please remultiplex input.
WARN: Previous sector: 289.839 - 289.871
WARN: Current sector: 289.869 - 289.901
WARN: Audio pts for channel 0 moves backwards by 180; please remultiplex input.