Because the “run length binary encoding”, does not track only null pixels. It switches data from row major / AoS to column major / SoA form, then each type get

Because the “run length binary encoding”, does not track only null pixels. It switches data from row major / AoS to column major / SoA form, then each type gets its own RLE scheme, timestamp remains on RLE-ing only 0 values but color and writer switch to every value being RLE’d (so each entry is a pair of a value and a repetition count).