basetrans: Remove ref in passthrough

Remove the requirement to have to return a ref to the input buffer when in
passthrough mode. This saves a few ref/unref cycles and fixes another 0.11
FIXME.

libs/gst/base/gstbasetransform.c

@@ -1364,6 +1364,8 @@ gst_base_transform_query_type (GstPad * pad)
   return types;
 }
 
+/* this function either returns the input buffer without incrementing the
+ * refcount or it allocates a new (writable) buffer */
 static GstFlowReturn
 default_prepare_output_buffer (GstBaseTransform * trans,
     GstBuffer * inbuf, GstBuffer ** outbuf)
@@ -1380,7 +1382,7 @@ default_prepare_output_buffer (GstBaseTransform * trans,
     /* passthrough, we will not modify the incomming buffer so we can just
      * reuse it */
     GST_DEBUG_OBJECT (trans, "passthrough: reusing input buffer");
-    *outbuf = gst_buffer_ref (inbuf);
+    *outbuf = inbuf;
   } else {
     /* we can't reuse the input buffer */
     if (priv->pool) {
@@ -1830,14 +1832,8 @@ no_qos:
   if (ret != GST_FLOW_OK || *outbuf == NULL)
     goto no_buffer;
 
-  /* FIXME 0.11:
-   * decrease refcount again if vmethod returned refcounted inbuf. This
-   * is because we need to make sure that the buffer is writable for the
-   * in_place transform. The docs of the vmethod say that you should return
-   * a reffed inbuf, which is exactly what we don't want :), oh well.. */
   if (inbuf == *outbuf) {
     GST_DEBUG_OBJECT (trans, "reusing input buffer");
-    gst_buffer_unref (inbuf);
   } else if (trans->passthrough) {
     /* we are asked to perform a passthrough transform but the input and
      * output buffers are different. We have to discard the output buffer and
@@ -1905,7 +1901,9 @@ no_qos:
   }
 
 skip:
-  /* only unref input buffer if we allocated a new outbuf buffer */
+  /* only unref input buffer if we allocated a new outbuf buffer. If we reused
+   * the input buffer, no refcount is changed to keep the input buffer writable
+   * when needed. */
   if (*outbuf != inbuf)
     gst_buffer_unref (inbuf);
 

libs/gst/base/gstbasetransform.h

@@ -180,10 +180,11 @@ struct _GstBaseTransform {
  *                         Subclasses can override this to do their own
  *                         allocation of output buffers.  Elements that only do
  *                         analysis can return a subbuffer or even just
- *                         increment the reference to the input buffer (if in
+ *                         return a reference to the input buffer (if in
  *                         passthrough mode). The default implementation will
  *                         use the negotiated allocator or bufferpool and
- *                         transform_size to allocate an output buffer.
+ *                         transform_size to allocate an output buffer or it
+ *                         will return the input buffer in passthrough mode.
  * @copy_metadata: Optional.
  *                 Copy the metadata from the input buffer to the output buffer.
  *                 The default implementation will copy the flags, timestamps and

plugins/elements/gstcapsfilter.c

@@ -330,9 +330,8 @@ gst_capsfilter_prepare_buf (GstBaseTransform * trans, GstBuffer * input,
 {
   GstFlowReturn ret = GST_FLOW_OK;
 
-  /* always ref input as output buffer */
+  /* always return the input as output buffer */
   *buf = input;
-  gst_buffer_ref (input);
 
   if (!gst_pad_has_current_caps (trans->sinkpad)) {
     /* Buffer has no caps. See if the output pad only supports fixed caps */

plugins/elements/gstidentity.c

@@ -388,15 +388,14 @@ gst_identity_prepare_output_buffer (GstBaseTransform * trans,
   /* only bother if we may have to alter metadata */
   if (identity->datarate > 0 || identity->single_segment) {
     if (gst_buffer_is_writable (in_buf))
-      *out_buf = gst_buffer_ref (in_buf);
+      /* reuse */
+      *out_buf = in_buf;
     else {
-      /* make even less writable */
+      /* copy */
-      gst_buffer_ref (in_buf);
+      *out_buf = gst_buffer_copy (in_buf);
-      /* extra ref is dropped going through the official process */
-      *out_buf = gst_buffer_make_writable (in_buf);
     }
   } else
-    *out_buf = gst_buffer_ref (in_buf);
+    *out_buf = in_buf;
 
   return GST_FLOW_OK;
 }