函数 av_rescale_q 

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

Rescale a 64-bit integer by 2 rational numbers.

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

This function is equivalent to av_rescale_q_rnd() with #AV_ROUND_NEAR_INF.

@see av_rescale(), av_rescale_rnd(), av_rescale_q_rnd()