Compression artefacts on large screens: banding, blocking and mosquito noise
Nothing is failing, and yet the picture looks cheap: banded skies, blocky fast motion, fuzz around edges. The encoding was tuned on a monitor at arm's length, and the living room is a different place.
Why the phone hides it and the television does not
A 720p rendition at 1.5 Mbps is fine on a six-inch screen because the display is small and the pixels are dense. Put the same rendition on a 55-inch panel viewed from three metres and the television upscales it to fill four times as many pixels, enlarging every compression decision the encoder made. Modern sets then apply sharpening and motion processing on top, which makes soft artefacts harder-edged and more visible rather than less.
The three artefacts viewers notice
Banding appears as visible steps in what should be smooth gradients - skies, fog, dark scenes, studio backgrounds. It is mostly a consequence of 8-bit colour depth combined with aggressive quantisation, and it is the artefact viewers complain about most because it sits in the middle of an otherwise clean image. Blocking shows up during fast motion or scene changes, when the encoder runs out of bits and falls back to coarse macroblocks. Mosquito noise is the shimmering fuzz around sharp edges and text, a by-product of the transform at low bitrates.
- Banding: stepped gradients in skies, fog and dark scenes, worst on 8-bit encodes.
- Blocking: macroblock edges in fast motion, confetti, crowds and rain.
- Mosquito noise: shimmering around edges, captions and graphics.
Fix it at the encoder, not the player
The player cannot invent detail that was thrown away, so the fixes are all upstream. Per-title or per-scene encoding allocates bitrate to the content that needs it: a football match and a talk show should not share a ladder, and a fixed-bitrate ladder wastes bits on one while starving the other. Adding rungs to the ladder makes quality steps smaller, so an ABR switch down is a slight softening rather than a visible collapse.
For premium content, HEVC at 10-bit is the single most effective change against banding, and it costs little at the encoder for a large improvement on gradients. Encoder tuning matters too: settings meant for screen content or low-latency streaming trade quality for speed in ways that show on a large panel. And the top rung has to be genuinely good - a 1080p rendition at 3 Mbps is not a 1080p experience on a big screen.
Judge it on a television
The recurring cause of all of this is that encoding profiles are approved on a desktop monitor. A ladder should be signed off on a real television of the size your audience owns, at normal viewing distance, with the set's default picture mode - because that is where the viewer will judge it.