One day, I was bored and decided to make a youtube downloader for Google Chrome called YT++. It adds a download button and a format selection menu pops up when you click it as well as a list of active downloads. All operations are done client-side.
This downloader works by requesting a video’s information via get_video_info in order to obtain a list of videos and codecs. On some videos, there are encrypted signatures which must be unscrambled. This extension does it by downloading the Youtube player code, searching for the relevant function that unscrambles the signature, finding its dependencies, and executing it all on-the-spot when you click the download button. This takes a few seconds but ensures that the extension will still work if Youtube changes the algorithm.
You can download version 2.3 of this extension here and you can install it by dragging the file into the extensions page in Google Chrome. You can then open any YouTube video and the download button will show up.
In the future, I may add a feature to convert videos to a requested format and the capacity to only have to download the YouTube player code when it gets changed. Please comment any feature requests or suggestions.
EDIT: Version 2.5 has been released with new features. Download it here.