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Youtube Video and Audio Downloader is an open-source project, downloading Youtube videos (using Firefox download manager) in all available formats (FLV, MP4, WebM, and 3GP) with video quality of your choice. It also contains a pure JavaScript library to extract the original audio file out of FLV videos. It also shipped with an offline tool to extract audio files out of FLV videos.

Features:
1. Download YouTube videos in all available format (FLV, MP4, WebM, and 3GP)
2. Extract original audio file. Useful to listen to the downloaded audio files on MP3 players. Audio extraction is only supported for FLV video format
3. Download video subtitle in all available languages (set the preferred language in the Settings)
4. Get comprehensive information about currently opened YouTube video (Middle click on the toolbar button)
5. Video conversion tools.

Notes:
1. In contrast to other YouTube audio downloader, this extension DOES NOT convert anything, instead it EXTRACTS the orignal audio file out of FLV video format. Thus if audio extraction is of your interest, you need to only download FLV video format.
2. Some mp3 players (e.g. iTunes) have problem playing AAC audio files (original extracted audio file). Read help info for workarounds.

Customization:
1. To add/remove the toolbar icon right click on the Firefox toolbar and select "Customize..."
2. To change settings go to Addon-manager -> Youtube video and audio downloader -> Options
3. To get information about Youtube videos such as all possible formats and their download links, first open a video in Firefox and when the toolbar icon is red, middle click on the toolbar button.
4. To extract audio files from FLV video, click on the toolbar button, go to Tools tab and then select Video conversion tool.
5. To extract all embed videos of current page, Ctrl + Left click on the toolbar button

Commands:
Left click: Open download panel
Middle click (Red icon): Get video information e.g.: all available formats and download links