framestep: implement backwards framestep

Update framestep document, we want to pass the flush flag in the step-done
message.

Add flush flag to the gstmessage.

Update examples to use the new step-done message api.

Implement framestep with playback rates < 0.0 too.

docs/design/draft-framestep.txt

@@ -180,13 +180,19 @@ messages
   "rate", G_TYPE_DOUBLE
      The rate and direction at which the frames were stepped.
 
-  "duration", G_TYPE_UINT64
-     The total duration of the stepped units in GST_FORMAT_TIME.
+  "flush", G_TYPE_BOOLEAN
+     If the stepped frames were flushed.
 
   "intermediate", G_TYPE_BOOLEAN
      If this is an intermediate step operation that completed.
 
- The message is emited by the element that performs the step operation.
+  "duration", G_TYPE_UINT64
+     The total duration of the stepped units in GST_FORMAT_TIME.
+
+ The message is emited by the element that performs the step operation. The
+ purpose is to return the duration in GST_FORMAT_TIME of the stepped media. This
+ especially interesting to align other stream in case of stepping frames on the
+ video sink element.
 
 
 Direction switch

gst/gstmessage.c

@@ -1641,8 +1641,9 @@ gst_message_get_stream_status_object (GstMessage * message)
  * @format: the format of @amount
  * @amount: the amount of stepped data
  * @rate: the rate of the stepped amount
- * @duration: the duration of the data
+ * @flush: is this an flushing step
  * @intermediate: is this an intermediate step
+ * @duration: the duration of the data
  *
  * This message is posted by elements when they complete a part, when @intermediate set
  * to TRUE, or a complete step operation.
@@ -1658,7 +1659,7 @@ gst_message_get_stream_status_object (GstMessage * message)
  */
 GstMessage *
 gst_message_new_step_done (GstObject * src, GstFormat format, guint64 amount,
-    gdouble rate, guint64 duration, gboolean intermediate)
+    gdouble rate, gboolean flush, gboolean intermediate, guint64 duration)
 {
   GstMessage *message;
   GstStructure *structure;
@@ -1667,8 +1668,9 @@ gst_message_new_step_done (GstObject * src, GstFormat format, guint64 amount,
       GST_QUARK (FORMAT), GST_TYPE_FORMAT, format,
       GST_QUARK (AMOUNT), G_TYPE_UINT64, amount,
       GST_QUARK (RATE), G_TYPE_DOUBLE, rate,
-      GST_QUARK (DURATION), G_TYPE_UINT64, duration,
-      GST_QUARK (INTERMEDIATE), G_TYPE_BOOLEAN, intermediate, NULL);
+      GST_QUARK (FLUSH), G_TYPE_BOOLEAN, flush,
+      GST_QUARK (INTERMEDIATE), G_TYPE_BOOLEAN, intermediate,
+      GST_QUARK (DURATION), G_TYPE_UINT64, duration, NULL);
   message = gst_message_new_custom (GST_MESSAGE_STEP_DONE, src, structure);
 
   return message;
@@ -1680,8 +1682,9 @@ gst_message_new_step_done (GstObject * src, GstFormat format, guint64 amount,
  * @format: result location for the format
  * @amount: result location for the amount
  * @rate: result location for the rate
- * @duration: result location for the duration
+ * @flush: result location for the flush flag
  * @intermediate: result location for the intermediate flag
+ * @duration: result location for the duration
  *
  * Extract the requested state from the request_state message.
  *
@@ -1691,8 +1694,8 @@ gst_message_new_step_done (GstObject * src, GstFormat format, guint64 amount,
  */
 void
 gst_message_parse_step_done (GstMessage * message, GstFormat * format,
-    guint64 * amount, gdouble * rate, guint64 * duration,
-    gboolean * intermediate)
+    guint64 * amount, gdouble * rate, gboolean * flush, gboolean * intermediate,
+    guint64 * duration)
 {
   g_return_if_fail (GST_IS_MESSAGE (message));
   g_return_if_fail (GST_MESSAGE_TYPE (message) == GST_MESSAGE_STEP_DONE);
@@ -1707,12 +1710,16 @@ gst_message_parse_step_done (GstMessage * message, GstFormat * format,
   if (rate)
     *rate = g_value_get_double (gst_structure_id_get_value (message->structure,
             GST_QUARK (RATE)));
-  if (duration)
-    *duration =
-        g_value_get_uint64 (gst_structure_id_get_value (message->structure,
-            GST_QUARK (DURATION)));
+  if (flush)
+    *flush =
+        g_value_get_boolean (gst_structure_id_get_value (message->structure,
+            GST_QUARK (FLUSH)));
   if (intermediate)
     *intermediate =
         g_value_get_boolean (gst_structure_id_get_value (message->structure,
             GST_QUARK (INTERMEDIATE)));
+  if (duration)
+    *duration =
+        g_value_get_uint64 (gst_structure_id_get_value (message->structure,
+            GST_QUARK (DURATION)));
 }

gst/gstmessage.h

@@ -385,10 +385,11 @@ GstMessage *	gst_message_new_state_dirty	(GstObject * src);
 
 /* STEP_DONE */
 GstMessage *    gst_message_new_step_done       (GstObject * src, GstFormat format, guint64 amount,
-                                                 gdouble rate, guint64 duration, gboolean intermediate);
+                                                 gdouble rate, gboolean flush, gboolean intermediate, 
+						 guint64 duration);
 void            gst_message_parse_step_done     (GstMessage * message, GstFormat *format, guint64 *amount,
-                                                 gdouble *rate, guint64 *duration, gboolean *intermediate);
-
+                                                 gdouble *rate, gboolean *flush, gboolean *intermediate,
+						 guint64 *duration);
 /* CLOCK_PROVIDE */
 GstMessage *	gst_message_new_clock_provide	(GstObject * src, GstClock *clock, gboolean ready);
 void		gst_message_parse_clock_provide (GstMessage *message, GstClock **clock,

libs/gst/base/gstbasesink.c

@@ -162,6 +162,7 @@ typedef struct
   guint64 duration;             /* the duration in time of the skipped data */
   guint64 start;                /* running_time of the start */
   gdouble rate;                 /* rate of skipping */
+  gboolean flush;               /* if this was a flushing step */
   gboolean intermediate;        /* if this is an intermediate step */
   gboolean need_preroll;        /* if we need preroll after this step */
 } GstStepInfo;
@@ -1476,22 +1477,23 @@ static void
 start_stepping (GstBaseSink * sink, GstSegment * segment,
     GstStepInfo * pending, GstStepInfo * current)
 {
-  gint64 start;
-
   GST_DEBUG_OBJECT (sink, "update pending step");
   memcpy (current, pending, sizeof (GstStepInfo));
   pending->valid = FALSE;
 
   /* get the running time of the current segment start and remember it */
-  start =
-      gst_segment_to_running_time (segment, segment->format, segment->start);
+  if (segment->rate > 0.0)
+    current->start =
+        gst_segment_to_running_time (segment, segment->format, segment->start);
+  else
+    current->start =
+        gst_segment_to_running_time (segment, segment->format, segment->stop);
 
   /* set the new rate */
-  segment->rate = current->rate;
+  segment->rate = segment->rate * current->rate;
 
   GST_DEBUG_OBJECT (sink, "step started at running_time %" GST_TIME_FORMAT,
-      GST_TIME_ARGS (start));
-  current->start = start;
+      GST_TIME_ARGS (current->start));
 
   if (current->amount == -1) {
     GST_DEBUG_OBJECT (sink, "step amount == -1, stop stepping");
@@ -1517,26 +1519,38 @@ stop_stepping (GstBaseSink * sink, GstSegment * segment,
       GST_TIME_FORMAT, GST_TIME_ARGS (*rstart), GST_TIME_ARGS (cstart));
 
   /* configure the duration of the elapsed segment */
-  current->duration = *rstart - current->start;
+  if (segment->rate > 0.0)
+    current->duration = *rstart - current->start;
+  else
+    current->duration = *rstop - current->start;
+
   GST_DEBUG_OBJECT (sink, "step elapsed running_time %" GST_TIME_FORMAT,
       GST_TIME_ARGS (current->duration));
 
   /* update the segment, discarding what was consumed, running time goes
    * backwards with the duration of the data we skipped. FIXME, this only works
    * in PAUSED. */
-  segment->time = gst_segment_to_stream_time (segment, segment->format, cstart);
-  segment->start = cstart;
+  if (segment->rate > 0.0) {
+    segment->time =
+        gst_segment_to_stream_time (segment, segment->format, cstart);
+    segment->start = cstart;
+
+    *rstart = current->start;
+    *rstop -= current->duration;
+  } else {
+    segment->stop = cstop;
+    *rstop = current->start;
+    *rstart -= current->duration;
+  }
   segment->accum = current->start;
 
   /* the clip segment is used for position report in paused... */
   memcpy (sink->abidata.ABI.clip_segment, segment, sizeof (GstSegment));
 
-  *rstart = current->start;
-  *rstop -= current->duration;
-
   message =
       gst_message_new_step_done (GST_OBJECT_CAST (sink), current->format,
-      current->amount, current->rate, current->duration, current->intermediate);
+      current->amount, current->rate, current->flush, current->intermediate,
+      current->duration);
   gst_message_set_seqnum (message, current->seqnum);
   gst_element_post_message (GST_ELEMENT_CAST (sink), message);
 
@@ -3392,6 +3406,7 @@ gst_base_sink_perform_step (GstBaseSink * sink, GstPad * pad, GstEvent * event)
     priv->pending_step.amount = amount;
     priv->pending_step.position = 0;
     priv->pending_step.rate = rate;
+    priv->pending_step.flush = flush;
     priv->pending_step.intermediate = intermediate;
     priv->pending_step.valid = TRUE;
 

tests/examples/stepping/framestep1.c

@@ -37,11 +37,11 @@ event_loop (GstElement * pipe)
         GstFormat format;
         guint64 amount;
         gdouble rate;
+        gboolean flush, intermediate;
         guint64 duration;
-        gboolean intermediate;
 
         gst_message_parse_step_done (message, &format, &amount, &rate,
-            &duration, &intermediate);
+            &flush, &intermediate, &duration);
 
         if (format == GST_FORMAT_DEFAULT) {
           g_message ("step done: %" GST_TIME_FORMAT " skipped in %"