Download speed: how it works and how to get more

The speed you see on each row is the real speed of the file arriving from YouTube. Here is what the extension does to make it fast, what is out of its hands, and what you can change.

What the extension does

YouTube slows down large single requests, so the extension asks for the file in parts of about 10 MB and keeps up to 6 parts in flight at once for each stream. A video and its audio are fetched side by side. The pieces are saved straight to your disk as they arrive, so memory stays low.

What decides your speed

Your internet connection. No downloader can beat it. A Wi-Fi signal that is weak or shared will show up directly in the number.
YouTube itself. Its servers can be slower at busy times, and some videos are served more slowly than others.
The quality you chose. 4K is many times larger than 720p, so it takes proportionally longer even at the same speed. The menu shows the estimated size before you start.
The last step. After the data arrives the file is built (MP4, MKV, MOV) or the sound is converted (MP3, M4A, AAC, WAV). The row says Muxing or Processing for this part; long videos take a little longer.

How to make it finish sooner

Switch on Pause while downloading in the settings, or pause the video yourself. A playing video uses the same connection.
Close tabs that stream video or sync big files.
Use a cable or sit close to the router. Turn off a VPN you do not need, as it often lowers speed.
Pick a lower quality when you do not need the best. 1080p looks great on most screens and is much smaller than 4K.
For audio only, use the Audio tab. It downloads far less data than a video.
Do not start many large downloads at once on a slow line: they share the same connection, so each one slows down.

Why a download can start slowly or stall

The first seconds show Starting while the extension prepares the download. If the speed drops to zero for a long time, pause and resume it, or stop it and try again. If it keeps failing, follow the fixes in order.

Disk space and size

Check that you have room before a 4K video or a long playlist. A 2160p video can be more than a gigabyte for a few minutes of footage.

Questions

Is there a speed limit in the extension?

No. The extension does not limit speed. What you get depends on your connection and on YouTube.

Why is MP3 fast but my 4K video slow?

A 4K file is far larger than the audio, so it takes longer at the same speed. Compare the sizes shown in the menu.

Does pausing the video really help?

Yes, because the player and the download share your connection. That is why Pause while downloading exists.