Reduce size of compiled ffmpeg.js for mobile client

[cuiyajie]

Now the size of ffmpeg.js is too large for mobile client. Now I only need the three commands as below. Is it possible to reduce the size below 1~2M？
ffmpeg -i [input file] [output file]
ffmpeg -i [input file] -b 500000 [output file]
ffmpeg -i [input file] -vf scale="'if(gt(a,4/3),640,-1)':'if(gt(a,4/3),-1,480)'" [output file]