What functionality is available through the YouTube API?

Where do I find the Developers Guide for the YouTube API? Do I need a developer key to use the YouTube API? What's the difference between the GData-based ... SkiptomaincontentWhatfunctionalityisavailablethroughtheYouTubeAPI?TheAPIprovidestheabilitytoretrievefeedsrelatedtovideos,users,andplaylists.Italsoprovidestheabilitytomanipulatethesefeeds,suchascreatingnewplaylists,addingvideosasfavorites,andsendingmesssages.TheAPIisalsoabletouploadvideos. Pleaseseethereferenceguideforacompletelistoffeeds. Additionally,thereisaJavaScriptAPIandaFlashAPIforthevideoplayer.trueGettingStartedWheredoIfindtheDevelopersGuidefortheYouTubeAPI?DoIneedadeveloperkeytousetheYouTubeAPI?What'sthedifferencebetweentheGData-basedAPIandthelegacyAPI?HowlongwilltheLegacyAPIcontinuetowork?WhatfunctionalityisavailablethroughtheYouTubeAPI?IstheYouTubeAPIbaseduponanystandardformatsorprotocols?WherecanIgotogethelpwithaproblemI'mexperiencing?WhatistheDeveloperKey?WhatistheClientID?WhatarethelimitsforuploadingwiththeAPI?GoogleappsMainmenuSearchHelpCenterfalse