Yep..live vocal over a backing track.
recorded at BBC studios, London 12.12.69 at the same session that produced this performance of 'Honky Tonk Women' for the Christmas Day edition of 'Top of The Pops -
http://www.youtube.com/watch?v=1KyFrDY1hz8&feature=related - according to nzentgraf.de they also did a version of 'Let It Bleed' (with a live vocal) for a TV special called Ten Years of What?' televised on 28/12/69 but I've never heard of this one.
Stunning vocal performance (dont ya just love the way he sings 'Gimme SHELTAH' at 3:16?)
This was included on a BBC special called "Pop Go The Sixties" which featured specially filmed performances by several acts, including The Who. It was shown on 31/12/69 - they reran it on 31/12/99 if I'm not mistaken, as I taped it at the time.
This version can also be found on the Mickboy remaster of 'Let It Bleed', "Get What You Need".
A busy week for the Stones, they'd just flown back from the Altamont debacle (6th December), recorded for two days at Olympic Studios (9th and 10th), taped this show on the 12th and then played two shows at London's Saville Theatre on Sunday the 14th.
They finished the year with another session at Olympic on the 18th (the one where Clapton played on 'Brown Sugar') and then another pair of ballroom dates at the Lyceum on the 21st.
Here is ten minutes of pro shot footage from one of the Saville Theatre shows on 14.12.69 -
http://www.youtube.com/watch?v=_0JIkHjEiL4