basesink: handle -1 step amounts

Define a 0 and -1 step amount. They used to almost do the same thing but now, 0
cancels/stops the current step and -1 keeps on stepping until the end of the
segment.

See https://bugzilla.gnome.org/show_bug.cgi?id=679378

diff --git a/docs/design/part-framestep.txt b/docs/design/part-framestep.txt
index 22d8895..7e5ecb8 100644 (file)
--- a/docs/design/part-framestep.txt
+++ b/docs/design/part-framestep.txt
@@ -101,8 +101,10 @@ The step event is created with the following fields in the structure:
      The format of the step units
 
   "amount", G_TYPE_UINT64
-     The amount of units to step. -1 resumes normal non-stepping behaviour to
-     the end of the segment.
+     The amount of units to step. A 0 amount immediately completes and can be
+     used to cancel the current step and resume normal non-stepping behaviour
+     to the end of the segment.
+     A -1 amount steps until the end of the segment.
 
   "rate", G_TYPE_DOUBLE
      The rate at which the frames should be stepped in PLAYING mode. 1.0 is

diff --git a/gst/gstsegment.c b/gst/gstsegment.c
index d0f1622..7ae8e60 100644 (file)
--- a/gst/gstsegment.c
+++ b/gst/gstsegment.c
@@ -440,8 +440,7 @@ gst_segment_to_stream_time (const GstSegment * segment, GstFormat format,
  * @position: the position in the segment
  *
  * Translate @position to the total running time using the currently configured
- * and previously accumulated segments. Position is a value between @segment
- * start and stop time.
+ * segment. Position is a value between @segment start and stop time.
  *
  * This function is typically used by elements that need to synchronize to the
  * global clock in a pipeline. The runnning time is a constantly increasing value

diff --git a/libs/gst/base/gstbasesink.c b/libs/gst/base/gstbasesink.c
index 8bced47..a96fa04 100644 (file)
--- a/libs/gst/base/gstbasesink.c
+++ b/libs/gst/base/gstbasesink.c
@@ -1496,16 +1496,30 @@ start_stepping (GstBaseSink * sink, GstSegment * segment,
     current->start_start = segment->start;
 
   if (current->format == GST_FORMAT_TIME) {
-    end = current->start + current->amount;
+    /* calculate the running-time when the step operation should stop */
+    if (current->amount != -1)
+      end = current->start + current->amount;
+    else
+      end = -1;
+
     if (!current->flush) {
+      gint64 position;
+
       /* update the segment clipping regions for non-flushing seeks */
       if (segment->rate > 0.0) {
-        segment->stop = gst_segment_to_position (segment, GST_FORMAT_TIME, end);
-        segment->position = segment->stop;
+        if (end != -1)
+          position = gst_segment_to_position (segment, GST_FORMAT_TIME, end);
+        else
+          position = segment->stop;
+
+        segment->stop = position;
+        segment->position = position;
       } else {
-        gint64 position;
+        if (end != -1)
+          position = gst_segment_to_position (segment, GST_FORMAT_TIME, end);
+        else
+          position = segment->start;
 
-        position = gst_segment_to_position (segment, GST_FORMAT_TIME, end);
         segment->time = position;
         segment->start = position;
         segment->position = position;
@@ -1590,8 +1604,9 @@ handle_stepping (GstBaseSink * sink, GstSegment * segment,
 {
   gboolean step_end = FALSE;
 
+  /* stepping never stops */
   if (current->amount == -1)
-    return TRUE;
+    return FALSE;
 
   /* see if we need to skip this buffer because of stepping */
   switch (current->format) {