A cop in L.A. named Brian Cappell got a call last month about a nine-month-old baby that was choking.  And he just happened to be in the right place at the right time.

He was driving in his car about a block away when the call came in.  And his chest-cam was on, so the whole thing is on video.

As soon as he heard where the little girl was, he floored it . . . got there in less than a minute . . . and the girl’s older sister flagged him down.

Then he grabbed the little girl from her mom . . . started hitting her on the back while holding her face-down in his other arm . . . and saved her life.

Once she started crying, he knew she was okay.  He says it was the best sound he’s ever heard in his life.

The girl’s mom told a reporter that she’s eternally grateful for what he did.  And they got to see each other again this past Monday when Brian received a commendation for it.

(CBS LA / Patch / WFLA)

(Here’s a photo of them together.)