Download audio messages from a Telegram channel or chat and turn them into a single MP3

audio_messages_to_mp3.rb

require 'dotenv'
Dotenv.load
require 'telegram/bot'
require 'json'
require 'open-uri'

token = ENV['TELEGRAM_TOKEN']

files = []
Telegram::Bot::Client.run(token) do |bot|
  # Grab updates from the Telegram bot
  updates = bot.api.get_updates(allowed_updates: ["channel_post"])["result"]

  # Select only voice posts from the past 24 hours
  updates.select! { |msg| msg['channel_post'] && msg['channel_post']['voice'] && msg['channel_post']['date'] && ((Time.now.to_i - msg['channel_post']['date']) < 86400) }

  # Iterate over each update
  updates.each.with_index do |msg, i|
    voice = msg['channel_post']['voice']

    # Get the Telegram file ID, then the file object itself
    file_id = voice['file_id']
    res = bot.api.get_file(file_id: file_id)
    file_path = res['result']['file_path']

    # Construct the URL the audio is available at and download it
    url = "https://api.telegram.org/file/bot#{token}/#{file_path}"
    puts "Fetching audio #{i}: #{file_path}"
    data = open(url).read
    temp_file = "/tmp/output-#{i}.mp3"
    File.open("/tmp/temp.oga", "w") { |f| f.puts data }

    # Normalize the format of the audio into a 44.1KHz 96kbps mono MP3
    `ffmpeg -loglevel panic -y -i /tmp/temp.oga -ab 96000 -ar 44100 -filter:a loudnorm -ac 1 #{temp_file}`

    files << temp_file
  end
end

# Join MP3s together with beeps in between each segment
`cat #{files.zip(['beep.mp3'] * (files.length - 1)).join(' ')} > output.mp3`

# Clean up the final MP3 (brew install mp3val)
`mp3val output.mp3 -f -nb`

puts "output.mp3 is built"