This is the most critical setting. By default, x265 enables SAO, which aggressively blurs the image to save bitrate. Disabling SAO ( no-sao=1 ) preserves fine details, textures, skin pores, and natural film grain, giving you a significantly sharper, "better than RARBG" output.
The slow preset is the entry point for x265's advanced lookahead and motion estimation algorithms. It is significantly slower than medium (often doubling encoding time) but yields noticeably better compression (quality per filesize). As the official x265 documentation notes, slower presets test more encoding options, using more computations to achieve the best quality at your selected bit rate. For RARBG, this was the minimum acceptable standard—anything faster would compromise the "magic" by limiting RD (Rate-Distortion) optimization levels. Importantly, the slow preset is the first preset to enable subme=3 or higher, which activates chroma SATD (Sum of Absolute Transformed Differences), a critical tool for color fidelity. rarbg x265 encoding settings better
The Ultimate RARBG x265 Encoding Guide: Settings for Better Quality and Compression This is the most critical setting