YouTube Youtube Format Selection

[Exxar]

I'm still waiting for an explanation as to why, when I select to download a 2GB movie, the download tap will show it's going to download a 1GB file. But you have to be quick, it only shows that for maybe 1 second.
I tried it with Amazon, Netflix and YouTube. It's all the same.

Youtube example: try downloading this video, Dave Moss seminar: https://www.youtube.com/watch?v=VeWOxVZFZPc
Select the highest quality 1080p video, which shows as a 1.8 GB file.
Quickly go to the download tab and see it's going to download a 950MB file. And that's what it does. Once the download progress bar more or less reaches the 50% mark, it suddenly jumps up, acting like it downloaded the full file, and the bar changes to processing.
And yes, I checked my router how much data it downloaded.


So, can someone explain what's going on here?

[jpp72]

It's a different streaming protocol.

The larger one is a bunch of chunks inside an m3u8 playlist and is using HLS streaming. The size displayed is a guesstimate and it usually is way off. I think it's because of the bitrate it thinks the video is using.. The https streaming is usually bang on for the size as the reported bitrate is accurate.

If you look at the results of yt-dlp's format list, the size is in grey and the ~ precedes the size to show it is "approximate". Not really approximate but basically all resolutions will have an m3u8 version and an https version but on the backend, it's the exact same video. So when you see there are only 2 options per resolution/codec/format, the lower size is what you will get no matter what you select.

Here are some screenshots showing what is happening: