recorder: Switch to webm

The vp8 codec provides better performance in pretty much all cases compared
to theora while still being free (as in not patent encumbered).

Also add a %T placeholder to the pipeline string which will be replaced
with the a thread count based on the target system.

https://bugzilla.gnome.org/show_bug.cgi?id=632595

data/org.gnome.shell.gschema.xml.in

@@ -101,11 +101,13 @@
         take care of its own output - this might be used to send the output
         to an icecast server via shout2send or similar. When unset or set
         to an empty value, the default pipeline will be used. This is currently
-        'videorate ! theoraenc ! oggmux' and records to Ogg Theora.
+        'videorate ! vp8enc quality=10 speed=2 threads=%T ! queue ! webmmux'
+        and records to WEBM using the VP8 codec. %T is used as a placeholder
+        for a guess at the optimal thread count on the system.
       </_description>
     </key>
     <key name="file-extension" type="s">
-      <default>'ogv'</default>
+      <default>'webm'</default>
       <_summary>File extension used for storing the screencast</_summary>
       <_description>
         The filename for recorded screencasts will be a unique filename

src/shell-recorder.c

@@ -147,11 +147,11 @@ G_DEFINE_TYPE(ShellRecorder, shell_recorder, G_TYPE_OBJECT);
  * (Theora does have some support for frames at non-uniform times, but
  * things seem to break down if there are large gaps.)
  */
-#define DEFAULT_PIPELINE "videorate ! theoraenc ! oggmux"
+#define DEFAULT_PIPELINE "videorate ! vp8enc quality=10 speed=2 threads=%T ! queue ! webmmux"
 
-/* The default filename pattern. Example shell-20090311b-2.ogg
+/* The default filename pattern. Example shell-20090311b-2.webm
  */
-#define DEFAULT_FILENAME "shell-%d%u-%c.ogg"
+#define DEFAULT_FILENAME "shell-%d%u-%c.webm"
 
 /* If we can find the amount of memory on the machine, we use half
  * of that for memory_target, otherwise, we use this value, in kB.
@@ -1493,11 +1493,47 @@ recorder_pipeline_closed (RecorderPipeline *pipeline)
   recorder_pipeline_free (pipeline);
 }
 
+/*
+ * Replaces '%T' in the passed pipeline with the thread count,
+ * the maximum possible value is 64 (limit of what vp8enc supports)
+ *
+ * It is assumes that %T occurs only once.
+ */
+static char*
+substitute_thread_count (const char *pipeline)
+{
+  char *tmp;
+  int n_threads;
+  GString *result;
+
+  tmp = strstr (pipeline, "%T");
+
+  if (!tmp)
+    return g_strdup (pipeline);
+
+#ifdef _SC_NPROCESSORS_ONLN
+    {
+      int n_processors = sysconf (_SC_NPROCESSORS_ONLN); /* includes hyper-threading */
+      n_threads = MIN (MAX (1, n_processors - 1), 64);
+    }
+#else
+    n_threads = 3;
+#endif
+
+  result = g_string_new (NULL);
+  g_string_append_len (result, pipeline, tmp - pipeline);
+  g_string_append_printf (result, "%d", n_threads);
+  g_string_append (result, tmp + 2);
+
+  return g_string_free (result, FALSE);;
+}
+
 static gboolean
 recorder_open_pipeline (ShellRecorder *recorder)
 {
   RecorderPipeline *pipeline;
   const char *pipeline_description;
+  char *parsed_pipeline;
   GError *error = NULL;
   GstBus *bus;
 
@@ -1509,9 +1545,12 @@ recorder_open_pipeline (ShellRecorder *recorder)
   if (!pipeline_description)
     pipeline_description = DEFAULT_PIPELINE;
 
-  pipeline->pipeline = gst_parse_launch_full (pipeline_description, NULL,
+  parsed_pipeline = substitute_thread_count (pipeline_description);
+
+  pipeline->pipeline = gst_parse_launch_full (parsed_pipeline, NULL,
                                               GST_PARSE_FLAG_FATAL_ERRORS,
                                               &error);
+  g_free (parsed_pipeline);
 
   if (pipeline->pipeline == NULL)
     {