BugFix MediaPlayer support for GIF animation

Playbin needs a videorate video filter, and thus user cannot change the video effect on a GIF

src/MediaPlayer.cpp

@@ -68,6 +68,7 @@ MediaPlayer::MediaPlayer()
     rate_change_ = RATE_CHANGE_NONE;
     decoder_name_ = "";
     video_filter_ = "";
+    video_filter_available_ = true;
     position_ = GST_CLOCK_TIME_NONE;
     loop_ = LoopMode::LOOP_REWIND;
 
@@ -346,8 +347,10 @@ void MediaPlayer::execute_open()
     g_object_set( G_OBJECT (pipeline_), "flags", flags, NULL);
 
     // hack to compensate for lack of PTS in gif animations
-    if (media_.codec_name.compare("image/gst-libav-gif") == 0)
-        video_filter_ = "videorate";
+    if (media_.codec_name.compare("image/gst-libav-gif") == 0) {
+        video_filter_ = "videorate rate=1.0";
+        video_filter_available_ = false;
+    }
 
     // Add a filter to playbin if provided
     if ( !video_filter_.empty()) {

src/MediaPlayer.h

@@ -258,6 +258,7 @@ public:
      * */
     void setVideoEffect(const std::string &pipeline_element);
     inline std::string videoEffect() { return video_filter_; }
+    inline bool videoEffectAvailable() { return video_filter_available_; }
     /**
      * Accept visitors
      * */
@@ -302,6 +303,7 @@ private:
     bool rewind_on_disable_;
     bool force_software_decoding_;
     std::string decoder_name_;
+    bool video_filter_available_;
     std::string video_filter_;
 
     // Play speed

src/SourceControlWindow.cpp

@@ -376,7 +376,8 @@ void SourceControlWindow::Render()
         {
             if (ImGui::MenuItem( ICON_FA_REDO_ALT "  Reload" ))
                 mediaplayer_active_->reopen();
-            if (ImGuiToolkit::MenuItemIcon(16, 16, "Gstreamer effect") )
+            if (ImGuiToolkit::MenuItemIcon(16, 16, "Gstreamer effect", nullptr,
+                                           false, mediaplayer_active_->videoEffectAvailable()) )
                 mediaplayer_edit_pipeline_ = true;
             if (ImGui::BeginMenu(ICON_FA_SNOWFLAKE "   On deactivation"))
             {