首先这三个函数所实践的都是a*b/c，它们所做的就是完善一下舍入方案，举个例子考虑c为0的情况等，三个函数的源码比较一下。
int64_t av_rescale_q(int64_t a, AVRational bq, AVRational cq) { return av_rescale_q_rnd(a, bq, cq, AV_ROUND_NEAR_INF); }
int64_t av_rescale_q_rnd(int64_t a, AVRational bq, AVRational cq, enum AVRounding rnd) { int64_t b = bq.num * (int64_t)cq.den; int64_t c = cq.num * (int64_t)bq.den; return av_rescale_rnd(a, b, c, rnd); }
可以看出av_rescale_q就是调用了av_rescale_q_rnd，只是第四个参数默认为AV_ROUND_NEAR_INF。
int64_t av_rescale_rnd(int64_t a, int64_t b, int64_t c, enum AVRounding rnd) { int64_t r = 0; av_assert2(c > 0); av_assert2(b >=0); av_assert2((unsigned)(rnd&~AV_ROUND_PASS_MINMAX)<=5 && (rnd&~AV_ROUND_PASS_MINMAX)!=4); if (c <= 0 || b < 0 || !((unsigned)(rnd&~AV_ROUND_PASS_MINMAX)<=5 && (rnd&~AV_ROUND_PASS_MINMAX)!=4)) return INT64_MIN; if (rnd & AV_ROUND_PASS_MINMAX) { if (a == INT64_MIN || a == INT64_MAX) return a; rnd -= AV_ROUND_PASS_MINMAX; } if (a < 0 && a != INT64_MIN) return -av_rescale_rnd(-a, b, c, rnd ^ ((rnd >> 1) & 1)); if (rnd == AV_ROUND_NEAR_INF) r = c / 2; else if (rnd & 1) r = c - 1; if (b <= INT_MAX && c <= INT_MAX) { if (a <= INT_MAX) return (a * b + r) / c; else return a / c * b + (a % c * b + r) / c; } else { #if 1 uint64_t a0 = a & 0xFFFFFFFF; uint64_t a1 = a >> 32; uint64_t b0 = b & 0xFFFFFFFF; uint64_t b1 = b >> 32; uint64_t t1 = a0 * b1 + a1 * b0; uint64_t t1a = t1 << 32; int i; a0 = a0 * b0 + t1a; a1 = a1 * b1 + (t1 >> 32) + (a0 < t1a); a0 += r; a1 += a0 < r; for (i = 63; i >= 0; i--) { a1 += a1 + ((a0 >> i) & 1); t1 += t1; if (c <= a1) { a1 -= c; t1++; } } return t1; } #else AVInteger ai; ai = av_mul_i(av_int2i(a), av_int2i(b)); ai = av_add_i(ai, av_int2i(r)); return av_i2int(av_div_i(ai, av_int2i(c))); } #endif }
可以看出av_rescale_q_rnd就是调用了av_rescale_rnd，只是做了一些完善。
