Vflash 0.6.18 — CPU media quantization

Reuse owned CPU RGB blocks during quantization, reducing temporary allocations while preserving input tensors and media output.

One 2048², 120-frame encoding comparison on eight CPU cores improved 15.7%; complete MP4 bytes were identical. This is encoding-stage evidence, not a GPU or complete-generation throughput claim. No new GPU qualification or thread-count default.

Validation: 17 focused media checks in a clean clone, source and wheel builds, standalone wheel import, privacy/lint hooks and bilingual documentation build.