Stuck pixel on A55 sensor
Oh I did not know that. Easy enough:-)
And I know it is not dust because I never switched lens in between shooting video and photos. Its a pretty bright grey dot.
Yes it is dust. A hot pixel is white, a dead pixel is black, dust is grey.
Your camera is not weatherproof. Dust can get inside a camera without removing the lens. Especially if you have a push focus lens.