Function vmaf_feature_score_at_index 

pub unsafe extern "C" fn vmaf_feature_score_at_index(
    vmaf: *mut VmafContext,
    feature_name: *const c_char,
    score: *mut f64,
    index: c_uint,
) -> c_int

Fetch feature score at specific index.

@param vmaf The VMAF context allocated with vmaf_init().

@param feature_name Name of the feature to fetch.

@param index Picture index.

@param score Score.

@return 0 on success, or < 0 (a negative errno code) on error.