These images are stills taken from a video I recorded this morning, at Hart Park in Bakersfield CA. Apologies for low quality. Am new to bird identifying, just curious about what I saw.
Similar in look to Wood ducks or Harlequin ducks, however I distinctly recall seeing a brown belly, separated by a horizontal white line from black/dark-colored back and head. There was also some red on the face. About the same size as the mallards they were swimming with.