UDL Helper is a powerful downloader for YouTube. In most cases, you can download MP3 or MP4 file with one click, otherwise, please, follow the link to uniDownloader website and use UDL Client software (Windows only). In addition to regular videos, you can download Shorts with no extra tools. The extension also supports downloading videos from other social media services: Instagram and Odnoklassniki. You are able to extract music from videos, thus UDL Helper is a powerful online video to MP3 converter: YouTube to MP3 converter, Instagram to MP3 converter, Odnoklassniki to MP3 converter. The extension can be used to take screenshots from online videos: it adds a screenshot button to YouTube and Odnoklassniki players. Also it adds a button to save photos easily from Instagram gallery. Most extension features are universal for any video service, but some features are service-specific. See details on UDL Helper’s page. Extension features for YouTube are listed below. Download YouTube video:

in MP4 format with sound (*);
with normal and high frame rates (e.g. 60 fps);
in resolutions: 360p, 720p [HD], 1080p [Full HD], 1440p 2K [Ultra HD], 2160p 4K [Ultra HD], 4320p 8K [Ultra HD].

Download YouTube audio (from video):

in MP4 and MP3 (**) formats;
at the highest possible bitrate.

Important: the list of available download options depends on characteristics of the original video! E.g. initially posted 360p @30 fps video without sound cannot be downloaded in Full HD @60 fps with sound. Other features of the browser extension:

Downloaded files have readable (human-friendly) names;
You can automatically get (copy to the clipboard) a direct link to the video (where such link exists);
Download videos to your phone or tablet by sending the link to your mobile device using a QR code (where such link exists);
The extension has stylish design with support of YouTube light and dark themes;
You can choose the button style: modern interface (appears on mouse over) and classic interface (appears on click);
"Embedded" videos loading support, i.e. YouTube videos hosted on third-party sites;
YouTube screenshot button, i.e. save frames while watching videos;
Support for downloading YouTube Shorts – you can get both video- and audio files;
Thoughtful help section with answers to frequently asked questions;
Several really useful settings :)

(*) In some cases, YouTube stores audio and video streams separately, therefore, to download video with sound they must be “glued” (muxing):

for small streams (up to 2 GB in total) the extension itself merges audio and video files, i.e. “on-the-fly” right in the browser;
for larger streams it is proposed to use UDL Client utility to avoid “freezing” of the browser tab.

(**) YouTube doesn't support MP3 format. So, to grab MP3 sound from YouTube videos, the extension uses built-in audio converter for files up to 2 GB or suggests using UDL Client software otherwize.