diff --git a/SessionCreator.cpp b/SessionCreator.cpp
index ad04f25..44f32b0 100644
--- a/SessionCreator.cpp
+++ b/SessionCreator.cpp
@@ -1151,11 +1151,22 @@ void SessionLoader::visit (SourceCallback &)
 {
 }
 
+void SessionLoader::visit (Play &c)
+{
+    bool p = true;
+    xmlCurrent_->QueryBoolAttribute("play", &p);
+    c.setValue(p);
+}
+
 void SessionLoader::visit (SetAlpha &c)
 {
     float a = 0.f;
     xmlCurrent_->QueryFloatAttribute("alpha", &a);
     c.setValue(a);
+
+    float d = 0.f;
+    xmlCurrent_->QueryFloatAttribute("duration", &d);
+    c.setDuration(d);
 }
 
 void SessionLoader::visit (SetDepth &c)
diff --git a/SessionCreator.h b/SessionCreator.h
index 73cab72..54a461f 100644
--- a/SessionCreator.h
+++ b/SessionCreator.h
@@ -71,6 +71,7 @@ public:
     void visit (Grab&) override;
     void visit (Resize&) override;
     void visit (Turn&) override;
+    void visit (Play&) override;
 
     static void XMLToNode(const tinyxml2::XMLElement *xml, Node &n);
     static void XMLToSourcecore(tinyxml2::XMLElement *xml, SourceCore &s);
diff --git a/SessionVisitor.cpp b/SessionVisitor.cpp
index ad3c210..479a741 100644
--- a/SessionVisitor.cpp
+++ b/SessionVisitor.cpp
@@ -764,9 +764,15 @@ void SessionVisitor::visit (SourceCallback &c)
     xmlCurrent_->SetAttribute("type", (uint) c.type());
 }
 
+void SessionVisitor::visit (Play &c)
+{
+    xmlCurrent_->SetAttribute("play", c.value());
+}
+
 void SessionVisitor::visit (SetAlpha &c)
 {
     xmlCurrent_->SetAttribute("alpha", c.value());
+    xmlCurrent_->SetAttribute("duration", c.duration());
 }
 
 void SessionVisitor::visit (SetDepth &c)
diff --git a/SessionVisitor.h b/SessionVisitor.h
index 5c0ddd3..cc1746a 100644
--- a/SessionVisitor.h
+++ b/SessionVisitor.h
@@ -77,6 +77,7 @@ public:
     void visit (Grab&) override;
     void visit (Resize&) override;
     void visit (Turn&) override;
+    void visit (Play&) override;
 
     static tinyxml2::XMLElement *NodeToXML(const Node &n, tinyxml2::XMLDocument *doc);
     static tinyxml2::XMLElement *ImageToXML(const FrameBufferImage *img, tinyxml2::XMLDocument *doc);
diff --git a/SourceCallback.cpp b/SourceCallback.cpp
index 6c22e67..4b6d806 100644
--- a/SourceCallback.cpp
+++ b/SourceCallback.cpp
@@ -133,43 +133,71 @@ SourceCallback *ResetGeometry::clone() const
     return new ResetGeometry;
 }
 
-SetAlpha::SetAlpha() : SourceCallback(), alpha_(0.f)
+SetAlpha::SetAlpha() : SourceCallback(), duration_(0.f), progress_(0.f), alpha_(0.f)
 {
-    pos_  = glm::vec2();
-    step_ = glm::normalize(glm::vec2(1.f, 1.f));   // step in diagonal by default
+    start_  = glm::vec2();
+    target_  = glm::vec2();
 }
 
-SetAlpha::SetAlpha(float alpha) : SetAlpha()
+SetAlpha::SetAlpha(float alpha, float duration) : SetAlpha()
 {
     alpha_ = CLAMP(alpha, 0.f, 1.f);
+    duration_ = duration;
 }
 
-void SetAlpha::update(Source *s, float)
+void SetAlpha::update(Source *s, float dt)
 {
     if (s && !s->locked()) {
         // set start position on first run or upon call of reset()
         if (!initialized_){
-            // initial position
-            pos_ = glm::vec2(s->group(View::MIXING)->translation_);
+            // initial mixing view position
+            start_ = glm::vec2(s->group(View::MIXING)->translation_);
+
+            // step in diagonal by default
+            glm::vec2 step = glm::normalize(glm::vec2(1.f, 1.f));
             // step in direction of source translation if possible
-            if ( glm::length(pos_) > DELTA_ALPHA)
-                step_ = glm::normalize(pos_);
+            if ( glm::length(start_) > DELTA_ALPHA)
+                step = glm::normalize(start_);
+            //
+            // target mixing view position
+            //
+            // special case Alpha = 0
+            if (alpha_ < DELTA_ALPHA) {
+                target_ = step;
+            }
+            // special case Alpha = 1
+            else if (alpha_ > 1.f - DELTA_ALPHA) {
+                target_ = step * 0.005f;
+            }
+            // general case
+            else {
+                // converge to reduce the difference of alpha using dichotomic algorithm
+                target_ = start_;
+                float delta = 1.f;
+                do {
+                    target_ += step * (delta / 2.f);
+                    delta = SourceCore::alphaFromCordinates(target_.x, target_.y) - alpha_;
+                } while (glm::abs(delta) > DELTA_ALPHA);
+            }
 
             initialized_ = true;
         }
 
-        // perform operation
-        float delta = SourceCore::alphaFromCordinates(pos_.x, pos_.y) - alpha_;
+        // time passed
+        progress_ += dt;
 
-        // converge to reduce the difference of alpha using dichotomic algorithm
-        if ( glm::abs(delta) > DELTA_ALPHA ){
-            pos_ += step_ * (delta / 2.f);
-            s->group(View::MIXING)->translation_ = glm::vec3(pos_, s->group(View::MIXING)->translation_.z);
-        }
-        // reached alpha target
-        else {
+        // perform movement
+        if ( ABS(duration_) > 0.f)
+            s->group(View::MIXING)->translation_ = glm::vec3(start_ + (progress_/duration_) * target_, s->group(View::MIXING)->translation_.z);
+
+        // time-out
+        if ( progress_ > duration_ ) {
+            // apply depth to target
+            s->group(View::MIXING)->translation_ = glm::vec3(target_, s->group(View::MIXING)->translation_.z);
+            // done
             finished_ = true;
         }
+
     }
     else
         finished_ = true;
@@ -378,6 +406,12 @@ SourceCallback *Play::reverse(Source *s) const
     return new Play(s->playing());
 }
 
+void Play::accept(Visitor& v)
+{
+    SourceCallback::accept(v);
+    v.visit(*this);
+}
+
 RePlay::RePlay() : SourceCallback()
 {
 }
diff --git a/SourceCallback.h b/SourceCallback.h
index 2c5b4f4..7650397 100644
--- a/SourceCallback.h
+++ b/SourceCallback.h
@@ -12,16 +12,16 @@ public:
 
     typedef enum {
         CALLBACK_GENERIC = 0,
-        CALLBACK_ALPHA,
-        CALLBACK_LOOM,
-        CALLBACK_GRAB,
-        CALLBACK_RESIZE,
-        CALLBACK_TURN,
-        CALLBACK_DEPTH,
-        CALLBACK_PLAY,
-        CALLBACK_REPLAY,
-        CALLBACK_RESETGEO,
-        CALLBACK_LOCK
+        CALLBACK_ALPHA = 1,
+        CALLBACK_LOOM = 2,
+        CALLBACK_GRAB = 3,
+        CALLBACK_RESIZE = 4,
+        CALLBACK_TURN = 5,
+        CALLBACK_DEPTH = 6,
+        CALLBACK_PLAY = 7,
+        CALLBACK_REPLAY = 8,
+        CALLBACK_RESETGEO = 9,
+        CALLBACK_LOCK = 10
     } CallbackType;
 
     static SourceCallback *create(CallbackType type);
@@ -56,16 +56,20 @@ public:
 
 class SetAlpha : public SourceCallback
 {
+    float duration_;
+    float progress_;
     float alpha_;
-    glm::vec2 pos_;
-    glm::vec2 step_;
+    glm::vec2 start_;
+    glm::vec2 target_;
 
 public:
     SetAlpha ();
-    SetAlpha (float alpha);
+    SetAlpha (float alpha, float duration = 0.f);
 
     float value () const { return alpha_;}
     void  setValue (float a) { alpha_ = a; }
+    float duration () const { return duration_;}
+    void  setDuration (float d) { duration_ = d; }
 
     void update (Source *s, float) override;
     void multiply (float factor) override;
@@ -154,6 +158,7 @@ public:
     SourceCallback *clone() const override;
     SourceCallback *reverse(Source *s) const override;
     CallbackType type () const override { return CALLBACK_PLAY; }
+    void accept (Visitor& v) override;
 };
 
 class RePlay : public SourceCallback
diff --git a/Visitor.h b/Visitor.h
index 7c9ed44..a8189c3 100644
--- a/Visitor.h
+++ b/Visitor.h
@@ -48,6 +48,7 @@ class Loom;
 class Grab;
 class Resize;
 class Turn;
+class Play;
 
 
 // Declares the interface for the visitors
@@ -101,6 +102,7 @@ public:
     virtual void visit (Grab&) {}
     virtual void visit (Resize&) {}
     virtual void visit (Turn&) {}
+    virtual void visit (Play&) {}
 };