函数 av_rescale_q_rnd 

pub unsafe extern "C" fn av_rescale_q_rnd(
    a: i64,
    bq: AVRational,
    cq: AVRational,
    rnd: AVRounding,
) -> i64

Rescale a 64-bit integer by 2 rational numbers with specified rounding.

The operation is mathematically equivalent to a * bq / cq.

@see av_rescale(), av_rescale_rnd(), av_rescale_q()