How I Downloaded a 2-Hour YouTube School Convocation Video Using yt-dlp

 

I had a 2-hour school convocation video on YouTube that I wanted to save for my own future reference. I first tried using a GUI downloader, but it kept spinning and never actually downloaded the video. The working solution was to use yt-dlp, plus a JavaScript runtime and FFmpeg support.

This guide documents the exact process that worked on Windows.

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1. Install yt-dlp

Download yt-dlp from the official GitHub release page:

https://github.com/yt-dlp/yt-dlp/releases

After downloading, place yt-dlp.exe in a folder such as:

D:\ch-software

Then open Command Prompt and go to that folder:

cd /d D:\ch-software

Test that it works:

yt-dlp --version

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2. Install Deno for YouTube JavaScript Challenges

When I first ran yt-dlp, I saw a warning like this:

No supported JavaScript runtime could be found.
YouTube extraction without a JS runtime has been deprecated.

To fix this, I installed Deno using Windows Package Manager:

winget install DenoLand.Deno

Then I closed Command Prompt, reopened it, and checked:

deno --version

If winget is not recognized, install or update App Installer from the Microsoft Store.

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3. Install FFmpeg

FFmpeg is important because YouTube livestream replays may download as HLS fragments. Without FFmpeg, the file may have timestamp issues or slight audio/video sync problems.

Install FFmpeg:

winget install Gyan.FFmpeg

Then close and reopen Command Prompt.

Check:

ffmpeg -version

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4. Check Available Video Formats

Before downloading, I checked what quality options were actually available:

yt-dlp -F "https://www.youtube.com/watch?v=yZFp6eo91rM"

The output showed this:

91 mp4 256x144     15
92 mp4 426x240     30
93 mp4 640x360     30
94 mp4 854x480     30
95 mp4 1280x720    30

This confirmed that the best available version was 720p, not 1080p. If YouTube does not provide a 1080p stream, yt-dlp cannot create one.

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5. Create a Custom Download Folder

I wanted to save the video into:

D:\my videos

So I created the folder:

mkdir "D:\my videos"

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6. Best Working Download Command

The final command that worked was:

yt-dlp --fixup force --remux-video mp4 -o "D:\my videos\%(title)s_%(height)sp.%(ext)s" "https://www.youtube.com/watch?v=yZFp6eo91rM"

What this command does

Command part	Meaning
yt-dlp	Runs the downloader
no -f option	Lets yt-dlp choose the best available format automatically
--fixup force	Forces post-download fixes for timestamp/container issues
--remux-video mp4	Repackages the video into a clean MP4 without re-encoding
-o "D:\my videos\%(title)s_%(height)sp.%(ext)s"	Saves the file to the custom folder and includes the resolution in the filename
YouTube URL	The video to download

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7. Important Note About -f best

I originally tried using:

-f "best"

But yt-dlp gave this warning:

"-f best" selects the best pre-merged format which is often not the best option.
To let yt-dlp download and merge the best available formats, simply do not pass any format selection.

So the better approach is to omit -f entirely and let yt-dlp pick the best available video/audio combination.

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8. Understanding the Fragment Download

During the download, I saw:

[hlsnative] Total fragments: 1216

This is normal for a YouTube livestream replay. YouTube serves the video as many small HLS fragments. yt-dlp downloads all the fragments and assembles them into one file.

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9. If Audio Is Slightly Out of Sync

After one earlier download, the file had a slight audio/video sync issue. The fix is to remux the MP4 using FFmpeg:

ffmpeg -i "input.mp4" -c copy "fixed_remux.mp4"

This does not reduce quality. It simply rebuilds the container.

If audio is still slightly off, shift the audio manually.

If audio is early

ffmpeg -i "input.mp4" -itsoffset 0.25 -i "input.mp4" -map 0:v -map 1:a -c copy "fixed_audio_delayed.mp4"

If audio is late

ffmpeg -i "input.mp4" -itsoffset -0.25 -i "input.mp4" -map 0:v -map 1:a -c copy "fixed_audio_advanced.mp4"

A small issue is usually around 0.1 to 0.4 seconds.

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Final Command to Keep for Future Use

For the same type of YouTube school convocation video, this is the command I would keep:

mkdir "D:\my videos"
yt-dlp --fixup force --remux-video mp4 -o "D:\my videos\%(title)s_%(height)sp.%(ext)s" "YOUTUBE_URL_HERE"

Example:

mkdir "D:\my videos"
yt-dlp --fixup force --remux-video mp4 -o "D:\my videos\%(title)s_%(height)sp.%(ext)s" "https://www.youtube.com/watch?v=yZFp6eo91rM"

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Bottom Line

The GUI downloader did not work, but yt-dlp worked once the proper supporting tools were installed. The key pieces were:

1. yt-dlp for downloading.

2. Deno for YouTube JavaScript challenge handling.

3. FFmpeg for clean MP4 remuxing and timestamp fixes.

4. No -f best; let yt-dlp choose the best available format automatically.

5. Use --fixup force and --remux-video mp4 for cleaner final output.