Snow, confetti and flashbulbs are what break a sports stream

Compression struggles with unpredictable motion, which is why a green pitch looks fine and a celebration turns to mush.

Watch a stream fall apart and note the moment. It is almost never the goal itself. It is the two seconds afterwards, when twenty thousand phone flashes go off and a camera pans across a stand.

Video compression works by prediction. The encoder keeps a picture in memory and mostly sends the differences, so anything that moves the way the encoder expects is nearly free. A footballer running across mown grass is cheap. Grass has low detail, the motion is smooth, and large parts of the frame are unchanged between one image and the next. This is why football on a modest stream looks better than its bitrate suggests.

Now break the prediction. Falling snow is thousands of small objects moving independently in front of a background, and no motion vector fits it. Confetti at a final is the same problem with colour. Ice is a low detail surface, which sounds easy, until you remember that low detail surfaces show banding, and the puck is a small fast object against them. Camera flashes change global brightness in a single frame, which invalidates the reference picture outright. Each of these forces the encoder to spend far more bits than the scene appears to deserve, and if the ceiling is fixed, something has to give.

What gives is usually the thing you care about. Rate control smears the shortfall across the whole frame, so the ball softens at the same time as the crowd does. The viewer concludes the service is bad. The service is fine. The scene is expensive.

I think the honest conclusion is that resolution has been oversold and frame rate undersold. A hundred frames a second at a moderate resolution serves fast sport better than a stack of pixels at fifty, because sport is a motion problem, and what viewers describe as sharp is usually temporal rather than spatial. Try to follow a struck puck at twenty five frames and you are watching a slideshow of positions.

Producers can help too, and mostly do not. A slow pan across a lit crowd is the most expensive shot in the rundown and it gets used as filler. Cut it. Hold on faces, hold still, let the encoder rebuild.

The best thing a broadcaster can do for picture quality costs nothing and lives in the gallery.