decrypt.mjs

import { readFileSync, writeFileSync } from 'fs'

async function get(url, options) {
  const controller = new AbortController()
  const { signal } = controller
  const res = await fetch(url, { ...options, signal })
  if (!res.ok) {
    controller.abort()
    throw new Error(`bad request (${res.status} ${res.statusText})`)
  }
  return await res.arrayBuffer()
}

const playlistFilename = process.argv[2]
const requestOptions = JSON.parse(process.argv[3] || null)

const playlist = readFileSync(playlistFilename, { encoding: 'utf-8' }).replaceAll('\r\n', '\n')

let key
let iv

let newPlaylist = ''

for (const line of playlist.split('\n')) {
  if (line[0] === '#') {
    const sepIdx = line.indexOf(':')
    const ext = line.substring(1, sepIdx)

    if (ext === 'EXT-X-KEY') {
      const params = line.substring(sepIdx + 1).split(',').map(p => { let idx = p.indexOf('='); return [p.substring(0, idx), p.substring(idx + 1)] })
      for (const [k, v] of params) {
        switch (k) {
          case 'METHOD':
            if (v !== 'AES-128') {
              console.error(`unknown encryption method: ${v}`)
              process.exit(1)
            }
            break
          case 'URI':
            const uri = JSON.parse(v)
            console.log('getting key')
            const rawKey = await get(uri, requestOptions)
            key = await crypto.subtle.importKey('raw', rawKey, 'AES-CBC', false, ['decrypt'])
            break
          case 'IV':
            iv = Buffer.from(v.substring(2), 'hex')
            break
          default:
            console.error(`unknown parameter ${k}`)
            process.exit(1)
        }
      }
    } else {
      newPlaylist += line + '\n'
    }
  } else {
    if (!line) {
      continue
    }

    if (!!key !== !!iv) {
      console.error('need both secret key and IV')
      process.exit(1)
    }

    const url = new URL(line)
    const filename = url.pathname.split('/').pop()
    console.log(`getting chunk (${filename})`)
    const buffer = await get(url, requestOptions)

    let out
    if (key) {
      out = await crypto.subtle.decrypt({ name: "AES-CBC", iv }, key, buffer)
    } else {
      out = buffer
    }

    writeFileSync(filename, Buffer.from(out))
    newPlaylist += filename + '\n'
  }
}

writeFileSync('new.m3u8', newPlaylist, { encoding: 'utf-8' })