Function preset_for_codec 

pub fn preset_for_codec(codec: Codec, preset: &str) -> String

Maps a generic preset name to codec-specific presets.

Software encoders get passthrough (except SVT-AV1 which maps to numeric presets). Hardware encoders get per-backend preset mapping:

• NVENC: p1..p7
• QSV: passthrough (veryfast..veryslow)
• VideoToolbox: realtime flag for fast presets
• VAAPI: compression_level 1..5
• AMF: speed/balanced/quality