segment: Added gst_segment_position_from_stream_time()

gst_segment_position_from_stream_time() will convert stream time into a
position in the segment so that gst_segment_to_stream_time() with that
position returns the same stream time. It will return -1 if the stream time
given is not inside the segment.

docs/gst/gstreamer-sections.txt

@@ -2565,6 +2565,7 @@ gst_segment_new
 gst_segment_copy
 gst_segment_free
 gst_segment_do_seek
+gst_segment_position_from_stream_time
 gst_segment_to_running_time
 gst_segment_to_running_time_full
 gst_segment_to_stream_time

gst/gstsegment.c

@@ -452,6 +452,69 @@ gst_segment_to_stream_time (const GstSegment * segment, GstFormat format,
   return result;
 }
 
+/**
+ * gst_segment_position_from_stream_time:
+ * @segment: a #GstSegment structure.
+ * @format: the format of the segment.
+ * @stream_time: the stream_time in the segment
+ *
+ * Convert @stream_time into a position in the segment so that
+ * gst_segment_to_stream_time() with that position returns @stream_time.
+ *
+ * Returns: the position in the segment for @stream_time. This function returns
+ * -1 when @stream_time is -1 or when it is not inside @segment.
+ *
+ * Since: 1.8
+ */
+guint64
+gst_segment_position_from_stream_time (const GstSegment * segment,
+    GstFormat format, guint64 stream_time)
+{
+  guint64 position, start, stop, time;
+  gdouble abs_applied_rate;
+
+  /* format does not matter for -1 */
+  if (G_UNLIKELY (stream_time == -1))
+    return -1;
+
+  g_return_val_if_fail (segment != NULL, -1);
+  g_return_val_if_fail (segment->format == format, -1);
+
+  start = segment->start;
+  time = segment->time;
+  /* this stream time was for a previous segment */
+  if (G_UNLIKELY (stream_time < segment->time))
+    return -1;
+
+  /* time must be known */
+  if (G_UNLIKELY (time == -1))
+    return -1;
+
+  if (G_LIKELY (segment->applied_rate > 0.0)) {
+    position = stream_time - time;
+  } else {
+    if (G_LIKELY (time > stream_time))
+      position = time - stream_time;
+    else
+      return -1;
+  }
+
+  abs_applied_rate = ABS (segment->applied_rate);
+
+  /* correct for applied rate if needed */
+  if (G_UNLIKELY (abs_applied_rate != 1.0))
+    position /= abs_applied_rate;
+
+  position += start;
+
+  stop = segment->stop;
+  /* outside of the segment boundary stop */
+  if (G_UNLIKELY (stop != -1 && position > stop))
+    return -1;
+
+  return position;
+}
+
 /**
  * gst_segment_to_running_time_full:
  * @segment: a #GstSegment structure.

gst/gstsegment.h

@@ -219,6 +219,7 @@ void         gst_segment_free                (GstSegment *segment);
 void         gst_segment_init                (GstSegment *segment, GstFormat format);
 
 guint64      gst_segment_to_stream_time      (const GstSegment *segment, GstFormat format, guint64 position);
+guint64      gst_segment_position_from_stream_time (const GstSegment * segment, GstFormat format, guint64 stream_time);
 guint64      gst_segment_to_running_time     (const GstSegment *segment, GstFormat format, guint64 position);
 
 gint         gst_segment_to_running_time_full (const GstSegment *segment, GstFormat format, guint64 position,

win32/common/libgstreamer.def

@@ -1154,6 +1154,7 @@ EXPORTS
 	gst_segment_is_equal
 	gst_segment_new
 	gst_segment_offset_running_time
+	gst_segment_position_from_stream_time
 	gst_segment_set_running_time
 	gst_segment_to_position
 	gst_segment_to_running_time