avformat/seek: add ff_rescale_interval() function

Refactors a function used by avformat/concat and avformat/imf.

Signed-off-by: Zane van Iperen <zane@zanevaniperen.com>

libavformat/internal.h

@@ -1023,4 +1023,24 @@ void avpriv_register_devices(const AVOutputFormat * const o[], const AVInputForm
  */
 int ff_format_shift_data(AVFormatContext *s, int64_t read_start, int shift_size);
 
+/**
+ * Rescales a timestamp and the endpoints of an interval to which the temstamp
+ * belongs, from a timebase `tb_in` to a timebase `tb_out`.
+ *
+ * The upper (lower) bound of the output interval is rounded up (down) such that
+ * the output interval always falls within the intput interval. The timestamp is
+ * rounded to the nearest integer and halfway cases away from zero, and can
+ * therefore fall outside of the output interval.
+ *
+ * Useful to simplify the rescaling of the arguments of AVInputFormat::read_seek2()
+ *
+ * @param[in] tb_in      Timebase of the input `min_ts`, `ts` and `max_ts`
+ * @param[in] tb_out     Timebase of the ouput `min_ts`, `ts` and `max_ts`
+ * @param[in,out] min_ts Lower bound of the interval
+ * @param[in,out] ts     Timestamp
+ * @param[in,out] max_ts Upper bound of the interval
+ */
+void ff_rescale_interval(AVRational tb_in, AVRational tb_out,
+                         int64_t *min_ts, int64_t *ts, int64_t *max_ts);
+
 #endif /* AVFORMAT_INTERNAL_H */

libavformat/seek.c

@@ -751,3 +751,13 @@ int avformat_flush(AVFormatContext *s)
     ff_read_frame_flush(s);
     return 0;
 }
+
+void ff_rescale_interval(AVRational tb_in, AVRational tb_out,
+                         int64_t *min_ts, int64_t *ts, int64_t *max_ts)
+{
+    *ts     = av_rescale_q    (*    ts, tb_in, tb_out);
+    *min_ts = av_rescale_q_rnd(*min_ts, tb_in, tb_out,
+                               AV_ROUND_UP   | AV_ROUND_PASS_MINMAX);
+    *max_ts = av_rescale_q_rnd(*max_ts, tb_in, tb_out,
+                               AV_ROUND_DOWN | AV_ROUND_PASS_MINMAX);
+}