A dog appears on screen and yours charges toward the television. Switch to something calmer or turn it off before they rehearse another long barking episode. Keep the television secure so your dog cannot knock it over or collide with the screen. Dogs can perceive motion on television, but that does not tell you exactly what your dog thinks they are seeing.
Watch for a pattern. Does the barking start with the picture, the sound of a bark, or fast movement? If your dog is distressed by ordinary household sounds or newly reacts to many things, ask your veterinarian about changes in hearing, vision, or wellbeing. For intense reactions, a qualified, reward-based behavior professional can help set a safe practice level.
Try a small, controlled version
At a low volume and with your dog comfortably away from the screen, play a very short clip that contains a mild version of the trigger. Reward your dog for noticing it and turning toward you. Stop before they bark. Across short sessions, change one thing at a time: sound, image, length, or distance. If they fixate, bark, freeze, or refuse food, make the next try easier. Do not repeatedly play full-volume dog videos to make them "get used to it."
Give your dog a mat or suitable chew in another room during programs likely to set them off. A dog who can relax while you watch a show does not have to watch it with you. If motion rather than sound sets your dog off, the movement and chasing guide may help you understand that pattern. For now, change the program or give your dog another room.
Sources: VCA Animal Hospitals: Can dogs see movement on TV?. Dogs Trust: Barking - causes, triggers and how to help.