Austin Seferian-Jenkins Dash Cam -- Talked Himself Into DUI Arrest ... 'I Gotta Take a Huge S***' (VIDEO)

TMZ Sports has obtained the dash cam footage from Austin Seferian-Jenkins' DUI arrest -- and he ALMOST got off scott free ... until he started running his drunken mouth. The ex-Bucs tight end was pulled over for an improper lane change after…