As part of the Android Operative system, there is a restriction that blocks installing applications outside of the Google Play Store.
YTMP3 converter is a free online website which allows to convert YouTube Video to mp3. Here you can easily convert YouTube video to mp3 (audio) files and download all mp3 audio for free.
ytbconverter supports all free website which allows the user to download high-quality mp3 audio. Ytmp3 is free and does not ask to install any software. YTMP3 converter only allows the user to convert videos up to a length of 2 hours.
This is the limitation of the website. However, they set this rule for a purpose. Ytbconverter allows the user to download unlimited YouTube to mp3 audio without any limitation.