How to build a YouTube Downloader in Python

Have you ever wanted to download the audio from a YouTube video? In this tutorial, I'm going to show you how to build your own free YouTube video downloader app. You can find the source code here

Prerequisities

What libraries/softwares will we need to download/configure?

youtube-dl (the python library)
FFmpeg
Click (the python library)

Before we can build our YouTube video and audio downloader, we have to download and configure our libraries. Since youtube-dl and click are both Python libraries, we can install both at the same time with pip:

pip install youtube-dl click

‍After these two libraries are done installing, we’re going to want to install FFmpeg, FFprobe, and FFplay. ffmpeg. FFmpeg is an open source and free software for handling, video, audio, and other multimedia files. We’ll be using this in conjunction with youtube-dl to convert the video we download into an audio file. This part is different for Windows and OSX users. First, we’re going to download the binaries from https://ffbinaries.com/downloads

If you’re a Windows user what you’ll want to do is download the binaries and unzip the files. You’ll see an executable file for each of the three ffbinaries we need, ffmpeg, ffprobe, and ffplay. Copy each executable file to a folder and make sure you know where that folder is. For the purposes of this tutorial, I copied it to the same folder that I am running the python program from. Later we’ll add an option to the request we send youtube_dl that will tell it where to find the program.

If you’re an OSX user, you’ll want to go to the site and download the binaries, and then add the location where you’ve downloaded them to to your PATH variable. Like so:

1. Run

sudo cp ./ffmpeg ./ffplay ./ffprobe /usr/local/bin

2. Open up ~/.zshrc with whatever text editor you’d like, I just run 

vim ~/.zshrc

3. Add the line 

PATH=”/usr/local/bin:$PATH”

YouTube Downloader App Creation

We’ll create two commands, one to download audio only, and one to download videos. Before we get into creating our actual commands, we have to initialize our CLI. An important note, all of your commands should go in-between the definition of apis() and the definition of main().

import click
 
@click.group()
def apis():
   """A CLI for getting transcriptions of YouTube videos"""
def main():
   apis(prog_name='apis')
 
if __name__ == '__main__':
   main()

YouTube Video Downloader App Code

The first thing we’ll need to do is make a download video function which will download the YouTube video from a link we pass to it as a .mp4 file. When we’re done, it should look like this:

Our YouTube download video function is going to specify the format that it wants the video in (mp4) and an output template that tells youtube-dl the way it wants the file saved. We’re going to set the name of the file to be equal to the YouTube id of the video, this is totally optional, I did it because I find that the title of the file can get long and cumbersome to work with in some settings, especially if there are spaces in it. Then we’ll call youtube-dl to save the file and have the function return the filename back to us.

import youtube_dl

@click.argument('link')
@apis.command()
def download_video(link):
   ydl_opts = {
       'format': 'mp4',
       'outtmpl': "./%(id)s.%(ext)s",
   }
   _id = link.strip()
   meta = youtube_dl.YoutubeDL(ydl_opts).extract_info(_id)
   save_location = meta['id'] + ".mp4"
   print(save_location)
   return save_location

‍The other function we need to make is a download audio from YouTube function which will download the audio from a YouTube link that we pass it as a .mp3 file. When we’re done, it should look like this:

Or if you decide you want to keep the video:

Like our YouTube download video function, our YouTube download audio function will also specify some options to youtube-dl. The extra options we’ll need to specify this time is to tell youtube-dl to use FFmpeg to convert the video file after processing and whether or not to keep the video.

@click.argument('link')
@click.option('-k', '--keep-video', is_flag=True, help="Pass this to keep the video")
@apis.command()
def download_audio(link, keep_video):
   ydl_opts = {
       'format': 'bestaudio/best',
       'postprocessors': [{
           'key': 'FFmpegExtractAudio',
           'preferredcodec': 'mp3',
           'preferredquality': '192',
       }],
       'ffmpeg-location': './',
       'outtmpl': "./%(id)s.%(ext)s",
       'keepvideo': 'True' if keep_video else 'False'
   }
   _id = link.strip()
   meta = youtube_dl.YoutubeDL(ydl_opts).extract_info(_id)
   save_location = meta['id'] + ".mp3"
   print(save_location)
   return save_location

‍That’s it. We’re done! It’s that easy. No more using sketchy sites with tons of ads to download your youtube videos or audios! See how to extend this into a CLI that will give you the transcript of the YouTube video. You can follow AssemblyAI for updates on Twitter @assemblyai, and you can follow me @yujian_tang