Looks fairly unremarkable to me. It's passing between the camera and the engine nozzle, so it must be very small -- maybe a speck of dust or a fleck of paint.

Looks fairly unremarkable to me. It's passing between the camera and the engine nozzle, so it must be very small -- maybe a speck of dust or a fleck of paint. Bear in mind that at this point in the video, the spacecraft is in direct sunlight and the background is pitch-black, so it doesn't take much to reflect enough light to be visible.