SFO TWR CTLR MISSPEAKS AND 2 ACFT IN POS ON RWYS 1L AND 1R ATTEMPT TO TAKE OFF TOGETHER.

Narrative

WE WERE IN POS AND HOLD ON RWY 1R AT SFO AND ACFT Y; A BRASILIA; WAS IN POS AND HOLD ON RWY 1L AT SFO. LNDGS WERE BEING CONDUCTED ON RWY 28L/R. I HEARD TWR SAY ACFT X CLRED FOR TKOF RWY 1R. THE FO READ BACK THE TKOF CLRNC; I TURNED ON THE LNDG LIGHTS AND WE COMPLETED THE TKOF CHKLIST AND THE FO BEGAN THE TKOF ROLL. WE HAD ONLY ROLLED ABOUT 50 FT WHEN TWR CANCELED OUR TKOF CLRNC AND TOLD US TO HOLD. WE NOTED THAT THE BRASILIA HAD BEGUN ITS TKOF ROLL AND CONTINUED TO TAKE OFF. NEITHER OF US REMEMBERED THE BRASILIA BEING CLRED FOR TKOF; BUT THE FO SAID THAT WHEN TWR HAD CLRED US FOR TKOF; TWR SAID 'ACFT Y...ACFT X CLRED FOR TKOF RWY 1R.' TWR DID NOT GIVE US A REASON WHY TKOF CLRNC WAS CANCELED AND I DIDN'T QUERY IT SINCE THE TWR FREQ WAS VERY BUSY AS USUAL IN SFO. AFTER ABOUT 1 MIN OR 2; TWR ONCE AGAIN CLRED US FOR TKOF WITHOUT ANY ADDITIONAL COMMENTS. BEST WE CAN FIGURE IS THAT THE BRASILIA; HAVING HEARD THE 'BRASILIA' AT THE BEGINNING OF OUR TKOF CLRNC; MISHEARD THE TWR AND THOUGHT THEY WERE CLRED FOR TKOF ON RWY 1L. BUT THAT IS ONLY A GUESS. NO RADIO CALLS WERE HEARD FROM TWR TO THE BRASILIA AFTER THEY TOOK OFF. SUPPLEMENTAL INFO FROM ACN 789977: SFO GND CHANGED CLRNC FROM RWY 28L SHORE 1 DEP TO SFO 8 RWY 1R. A MIN LATER; TWR CLEARS US TO TAKE OFF. WE DECLINE. I REWORK FMC FOR DEP; CHK PERFORMANCE; RESET BAROMETRIC BUG AND RE-BRIEF NEW DEP AND ENG OUT PROC. TWR CLEARS US TO POS AND HOLD RWY 1R. THEN TWR CLEARS; 'ACR Y; ERR -- I MEAN; ACR X; CLRED TO TAKE OFF RWY 1R.' I READ BACK 'ACR X CLRED FOR TKOF RWY 1R.' AT THIS POINT I NOTICE A BRASILIA BEGINNING TO ACCELERATE ON RWY 1L. WE WENT MAYBE 30 FT WHEN TWR SAID 'ACR X CANCEL TKOF CLRNC.' IN RETROSPECT; I BELIEVE ACFT Y HEARD ITS CALL SIGN MISTAKENLY SAID IN THE CLRNC AND HE MAY HAVE RESPONDED AT THE SAME TIME I DID.