IEBPROJECT CASE STUDY
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The quality list opened upward over the video, listing 2160p60 down to 144p with resolution, frame rate and megabytes for each, plus an audio MP3 row at the bottom

Browser extensionDrawing 30 of 43

Square
Downloader

YouTube stopped serving HD video as one file, so a normal downloader has nothing left to grab. This one copies the bytes as the player decodes them, then puts the file back together with ffmpeg. It all runs in the browser with no server involved.

Sheet 02 of 09/Why

Free and open source

The extension this is modeled on isn't open source and puts the good video qualities behind a paywall, so I kept this one easy to check. It uses three permissions, only runs on YouTube, and has no server code at all.

A tight crop of the download bar on its own, showing only the quality picker, the subtitles checkbox, the Download button and an overflow dot menu
PL 06The full interface is this one strip, with a quality picker, a checkbox and a button.

Sheet 03 of 09/Capture

How it captures video

There's no file to catch anymore, so it hooks the player's appendBuffer call and copies every byte that goes past. It gets the rest by nudging a paused player forward, over and over.

Sheet 04 of 09/Codec

Lying about codecs

It also lies to YouTube about which codecs the browser can play, so YouTube sends VP9 instead of AV1, which the bundled ffmpeg can't process.

Sheet 05 of 09/Interface

The part I built

The capture engine came with the fork. I built the bar and everything else here, including the quality list, which pulls real sizes straight off the player's own format table.

A YouTube watch page with a horizontal download bar inserted below the video, showing a quality picker reading 1080p60, a subtitles checkbox and a blue Download button
PL 02The bar sits in the page under the player and above the title, and it never covers the video controls.
The same quality list rendered on a dark grey panel, with the clip range inputs visible below it
PL 03The same list in dark mode, which follows YouTube's own theme whatever the operating system is set to.
A small overflow menu open beside the download button with three entries reading Save as, Clip range, and H.264 compatible slower
PL 04The three options that needed a menu: Save as, clip range, and H.264 for older players.
The bar showing clip range inputs set from 0:00:05 to 0:00:13 and a completed status line beginning Done, with a filled progress bar behind it
PL 05An eight-second clip, finished and reported right in the bar, with no floating card.

Sheet 06 of 09/Failure

When ffmpeg fails

The merge step doesn't trust ffmpeg to work the first time, so it keeps a couple of fallback ways to make the file and tries them in order before it gives up.

Sheet 07 of 09/Credit

Who wrote what

The capture engine is the hard part, and it's Triangle Downloader's. Everything you see and click is what I added on top of it.

Sheet 08 of 09/Limits

What it can't do

It needs an ad blocker running, and no version of it will get around that. Without one, YouTube splices ads into the stream and the capture chokes on them.

Sheet 09 of 09/Source

Inspect the work