youtube_download.py

# coding: utf-8

from pytube import (
        Playlist as P,
        Stream as S,
        YouTube as Y
)
from pytube.cli import on_progress

async def download_best_quality_streams(youtube: Y):
    hq = best_quality_stream(youtube, must_have_audio=False)
    hq_with_audio = best_quality_stream(youtube, must_have_audio=True)

    def resolution(stream: S) -> int:
        string = stream.resolution # 2160p / 1080p / 720p etc.
        number = string[:-1] # Hardcoded logic
        return int(number)

    # if the best quality stream has no audio track
    if not hq.includes_audio_track:
        # and its resolution is lower or equal to the one has audio
        if resolution(hq) <= resolution(hq_with_audio):
            video = hq_with_audio
            audio = None

            print(f"Downloading the {video.resolution} video with audio")
        else:
            video = hq
            audio = youtube.streams.get_audio_only()

            print(f"Downloading the {video.resolution} video and the audio track separately")

    video.download()
    if audio:
        audio.download()

def best_quality_stream(youtube: Y, must_have_audio: bool=False) -> S:
    streams = youtube.streams

    if must_have_audio:
        streams = streams.filter(
            custom_filter_functions=[
                has_audio
            ]
        )

    return streams.order_by('resolution').desc().first()

def has_audio(stream: S) -> bool:
    return stream.includes_audio_track