BLUE optical-flow compositor cuts surveillance storage by up to 39%

Continuous surveillance cameras waste bits re-encoding unchanged backgrounds. A new pre-encode compositor called BLUE solves this by maintaining a persistent 'seed frame' of the background and substituting stale background pixels before the encoder runs. The encoder then emits near-free SKIP macroblocks for frozen areas, while foreground pixels pass through at full quality.

Tested on all 308 annotated subclips from the VIRAT Ground Surveillance dataset with a six-point CRF sweep using x264 and x265, BLUE achieves a mean file size reduction of 34.6% (x264) and 39.4% (x265) at CRF28. Foreground PSNR (measured only over object-annotation bounding boxes) is preserved or improved on 60.7% of clips, with a mean gain of +0.36 dB and a maximum of +5.48 dB. Full-frame VMAF drops by a median of 6.75–8.59 points, but a lightweight deployment gate analyzes a 2-second prefix to identify the 40% of clips where degradation is near-imperceptible (Delta VMAF <= -2.9). This selective activation strategy retains both storage benefits and acceptable perceptual fidelity, making BLUE a practical addition to existing codec pipelines for security and surveillance systems.