函数 av_rescale_rnd 

pub unsafe extern "C" fn av_rescale_rnd(
    a: i64,
    b: i64,
    c: i64,
    rnd: AVRounding,
) -> i64

Rescale a 64-bit integer with specified rounding.

The operation is mathematically equivalent to a * b / c, but writing that directly can overflow, and does not support different rounding methods. If the result is not representable then INT64_MIN is returned.

@see av_rescale(), av_rescale_q(), av_rescale_q_rnd()