ffmpeg multitrack to stems

ffmpeg-stem-management.js

/*
it's a pain in the ass to manage and using ffmpeg is kinda easiest. so grab your multitracks and just make a comma/semicolon
separated list. 

vox=Ld Vocals.mp3,Vocal FX.mp3,BGV 1.mp3,Adlibs.mp3,BGV 2.mp3,BGV 3.mp3;
drums=Snare.mp3,Percussion.mp3,Claps.mp3,Kick.mp3;
bass=808.mp3,Pads.mp3;
other=Guitar.mp3,Strings.mp3

this generates a string (multiple ffmpeg commands) that makes the 4 stems that you can just run in your terminal.
the stems will be named after the label on the left of the '='
run in the directory the files are in. if you need help getting ffmpeg...

make the 'config' into one line:

vox=Ld Vocals.mp3,Vocal FX.mp3,BGV 1.mp3,Adlibs.mp3,BGV 2.mp3,BGV 3.mp3;drums=Snare.mp3,Percussion.mp3,Claps.mp3,Kick.mp3;bass=808.mp3,Pads.mp3;other=Guitar.mp3,Strings.mp3

to make stem files, just use ffmpeg's amerge, it's simple and diverse enough.
> ffmpeg -i a.mp3 -i b.mp3 -i c.mp3 -filter_complex "[0:a][1:a][2:a]amerge=inputs=3,pan=stereo|c0<c0+c2+c4|c1<c1+c3+c5[a]" -map "[a]" "d.mp3"
this is what you run to merge 3 tracks into one stem. figure out the pattern for n tracks

i just open up a terminal -> node or chrome -> inspect and run quick scripts. i realize my life is ratchet

also realized i wrote this fluid enough to support any config, not just 4 stems like what fits my needs. whoops
*/

const stemConfig = 'vox=Ld\ Vocals.mp3,Vocal\ FX.mp3,BGV\ 1.mp3,Adlibs.mp3,BGV\ 2.mp3,BGV\ 3.mp3;drums=Snare.mp3,Percussion.mp3,Claps.mp3,Kick.mp3;bass=808.mp3,Pads.mp3;other=Guitar.mp3,Strings.mp3'

const generateCmds = stemConfig => stemConfig.split(';').map(config => [config.split('=')[0], config.split('=')[1].split(',').map(track => `"${track}"`)]).map(([output, tracks]) => `ffmpeg -i ${tracks.join(' -i ')} -filter_complex "${tracks.map((_,i) => `[${i}:a]`).join('')}amerge=inputs=${tracks.length},pan=stereo|c0<${`c${tracks.map((_,i) => i * 2).join('+c')}`}|c1<${`c${tracks.map((_,i) => i * 2 + 1).join('+c')}`}[a]" -map "[a]" "${output}.mp3"`).join(' && ')

// one liners makes copy pasta easier and it's a sad world we live in that i live by this. here, it's not magic:

stemConfig
  .split(';')
  .map((config) => [
    config.split('=')[0],
    config
      .split('=')[1]
      .split(',')
      .map((track) => `"${track}"`),
  ]) // [['vox', [...]], ['drums', [...]], ...]
  .map(
    ([output, tracks]) =>
      `ffmpeg \
      -i ${tracks.join(' -i ')} \
      -filter_complex "${tracks.map((_, i) => `[${i}:a]`).join('')}amerge=inputs=${tracks.length},pan=stereo|c0<${`c${tracks.map((_, i) => i * 2).join('+c')}`}|c1<${`c${tracks.map((_, i) => i * 2 + 1).join('+c')}`}[a]" \
      -map "[a]" \
      "${output}.mp3"`
  )
  .join(' && '); // just to run them all at once

/*
to do
don't hard code mp3 you idiot
lol knowing ffmpeg i could do this all with one run isntead of &&-ing
ehh good enough, im not gonna explain the filter complex. DM for deets hahaha
*/

// ugg for peak lazy (chrome) (plus that prefix thing haha)
const CMDtoClip = (stemConfig, prefix = '') => copy(stemConfig.split(';').map(config => [config.split('=')[0], config.split('=')[1].split(',').map(track => `"${track}"`)]).map(([output, tracks]) => `ffmpeg -i ${tracks.join(' -i ')} -filter_complex "${tracks.map((_,i) => `[${i}:a]`).join('')}amerge=inputs=${tracks.length},pan=stereo|c0<${`c${tracks.map((_,i) => i * 2).join('+c')}`}|c1<${`c${tracks.map((_,i) => i * 2 + 1).join('+c')}`}[a]" -map "[a]" "${prefix}${output}.mp3"`).join(' && '))