Chroma weighted prediction
Like luma weighted prediction, dramatically improves compression in fades. Up to 4-8db chroma PSNR gain in extreme cases (short, perfect fade-outs). On actual videos, helps up to ~1% overall. One example video with a decent number of fades (ef OP): 0.8% bitrate reduction overall, 7% bitrate reduction just counting chroma. Fixes a lot of artifacts in fades at lower bitrates. Original patch by Dylan Yudaken <email@example.com>.
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