Youtube-dl playlist downloads are done sequentially. However you can speed things up by running multiple youtube-dl processes in paralell.

Requirements

This will only work with PowerShell 7, not PowerShell 5.* which comes bundled with windows 10/11.

Check your Powershell version with

Get-Host | Select-Object Version 

If you are running the preinstalled windows powershell 5, update it: instructions here.

Quick tip: Updating to powershell 7 with winget

If you have winget already installed, just run

winget install --name PowerShell --exact --source winget

Downloading 5 videos simultaneously from a youtube playlist

Launch powershell 7 and execute

 youtube-dl --get-id "YOUR_YOUTUBE_PLAYLIST_URL" | ForEach-Object -Parallel { youtube-dl.exe -f best "$_"; } -ThrottleLimit 5

This will run 5 youtube-dl.exe processes simultaneously instead of each video only downloading after the previous is finished.