YouTube has all the buttons—Upload, Browse, Subscribe etc.—, but it doesn't come with an inbuilt “Download” button. Viewers have to use third party software to download the videos from YouTube. Why is that?
Youtube – Why doesn’t YouTube have a download button
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Related Solutions
I am unsure what changed, but I suspect YouTube changed their URLs so you can not get a video without matching cookies. This prevents 3rd party sites from showing you ads and giving you download links.
I can tell you this link (pasted at the very bottom), which I got from your video, WORKS for me. However if I paste it in my other instance of Firefox (which has different cookies for the site) this link does NOT work.
I suggest using a userscript. I like YouTube Enhancer.
If you need to do this in code I do see the link(s?) in var swfConfig =
to make it easy for me to read I did a full escape using this handy script.
The Google Data Liberation Front provides Google Takeout, which allows Google users to export their data to a downloadable ZIP file. Here is the link to export one's Youtube videos: https://www.google.com/settings/takeout/custom/youtube . It will create an archive containing all the original uploaded videos.
Best Answer
Because the premiss of the site is that you go back to view your favourite videos so you can see (more) advertising, sponsored links etc.
If you download the videos you could watch them as many times as you wanted without seeing all this.
There's also the small matter of copyright - you only have the right to view the videos, not copy and (potentially) redistribute it.