FFmpeg学习笔记-API理解

av_compare_ts：

在音视频流复用（MUX）的时候比较时间戳，根据时间戳的先后顺序交叉写入音频包或视频包

/**

 * Compare two timestamps each in its own time base.
 *
 * @return One of the following values:
 *         - -1 if `ts_a` is before `ts_b`
 *         - 1 if `ts_a` is after `ts_b`
 *         - 0 if they represent the same position
 *
 * @warning
 * The result of the function is undefined if one of the timestamps is outside
 * the `int64_t` range when represented in the other's timebase.
 */

int av_compare_ts(int64_t ts_a, AVRational tb_a, int64_t ts_b, AVRational tb_b);

av_rescale

/**
 * Rescale a 64-bit integer with rounding to nearest.
 *
 * The operation is mathematically equivalent to `a * b / c`, but writing that
 * directly can overflow.
 *
 * This function is equivalent to av_rescale_rnd() with #AV_ROUND_NEAR_INF.
 *
 * @see av_rescale_rnd(), av_rescale_q(), av_rescale_q_rnd()
 */
int64_t av_rescale(int64_t a, int64_t b, int64_t c) av_const;

av_rescale_rnd

/**
 * 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.
 *
 * @see av_rescale(), av_rescale_q(), av_rescale_q_rnd()
 */
int64_t av_rescale_rnd(int64_t a, int64_t b, int64_t c, enum AVRounding rnd) av_const;

av_rescale_q

/**
 * 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()
 */
int64_t av_rescale_q(int64_t a, AVRational bq, AVRational cq) av_const;

av_rescale_q_rnd

转换pts，将一个时间基（in_stream）下的pts转换到另一个时间基（out_stream）下的pts
/**
 * 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()
 */
int64_t av_rescale_q_rnd(int64_t a, AVRational bq, AVRational cq,
                         enum AVRounding rnd) av_const;

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