gst-launch的-v参数

-v参数

先看一个简单的例子：

gst-launch的pipeline，增加-v参数就可以输出caps的详细信息，包括我们想要的codec_data，那么，这个-v参数是怎么输出这些的，就需要深入跟踪下代码，因为这个输出不受GST_DEBUG的控制，是直接输出到terminal的。

$ gst-launch-1.0 filesrc location=~/h264.mp4 ! qtdemux !  fakesink -v
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
/GstPipeline:pipeline0/GstFakeSink:fakesink0.GstPad:sink: caps = video/x-h264, stream-format=(string)avc, alignment=(string)au, \
level=(string)3.1, profile=(string)high, codec_data=(buffer)0164001fffe100196764001facd9405005ba1000000300100000030320f183196001000568ebecb22c, \
width=(int)1280, height=(int)720, framerate=(fraction)25/1, pixel-aspect-ratio=(fraction)1/1
Pipeline is PREROLLED ...
Setting pipeline to PLAYING ...
Redistribute latency...
New clock: GstSystemClock
Got EOS from element "pipeline0".
Execution ended after 0:00:00.001151180
Setting pipeline to NULL ...
Freeing pipeline ...

在gst-launch的代码中，-v参数的作用是输出状态信息和属性通知，如果有verbose参数，会先增加deep_notify处理函数：

{"verbose", 'v', 0, G_OPTION_ARG_NONE, &verbose,N_("Output status information and property notifications"), NULL},if (verbose) {deep_notify_id =gst_element_add_property_deep_notify_watch (pipeline, NULL, TRUE);
}

gst_element_property_deep_notify_cb

gst_element_property_deep_notify_cb在这里是deep_notify信号回调函数：

gulong
gst_element_add_property_deep_notify_watch (GstElement * element,const gchar * property_name, gboolean include_value)
{const gchar *sep;gchar *signal_name;gulong id;g_return_val_if_fail (GST_IS_ELEMENT (element), 0);sep = (property_name != NULL) ? "::" : NULL;signal_name = g_strconcat ("deep-notify", sep, property_name, NULL);id = g_signal_connect (element, signal_name,G_CALLBACK (gst_element_property_deep_notify_cb),GINT_TO_POINTER (include_value));g_free (signal_name);return id;
}

跟踪进入gst_element_property_deep_notify_cb函数，gst_message_new_property_notify会先创建新的property消息，然后post message。

gst_message_new_property_notify

gst_message_new_property_notify中构造MESSAGE_PROPERTY_NOTIFY类型的message，message post之后，就会在gst-launch中接收处理。

GstMessage *
gst_message_new_property_notify (GstObject * src, const gchar * property_name,GValue * val)
{GstStructure *structure;GValue name_val = G_VALUE_INIT;g_return_val_if_fail (property_name != NULL, NULL);structure = gst_structure_new_id_empty (GST_QUARK (MESSAGE_PROPERTY_NOTIFY));g_value_init (&name_val, G_TYPE_STRING);/* should already be interned, but let's make sure */g_value_set_static_string (&name_val, g_intern_string (property_name));gst_structure_id_take_value (structure, GST_QUARK (PROPERTY_NAME), &name_val);if (val != NULL)gst_structure_id_take_value (structure, GST_QUARK (PROPERTY_VALUE), val);return gst_message_new_custom (GST_MESSAGE_PROPERTY_NOTIFY, src, structure);
}

gst-lauch之GST_MESSAGE_PROPERTY_NOTIFY

在gst-launch的中，GST_MESSAGE_PROPERTY_NOTIFY的处理分支，会先解析message的val，然后在最后通过gst_print打印出来，这就是为什么通过增加-v参数就能获取codec_data了。

case GST_MESSAGE_PROPERTY_NOTIFY:{const GValue *val;const gchar *name;GstObject *obj;gchar *val_str = NULL;gchar **ex_prop, *obj_name;if (quiet)break;gst_message_parse_property_notify (message, &obj, &name, &val);/* Let's not print anything for excluded properties... */ex_prop = exclude_args;while (ex_prop != NULL && *ex_prop != NULL) {if (strcmp (name, *ex_prop) == 0)break;ex_prop++;}if (ex_prop != NULL && *ex_prop != NULL)break;obj_name = gst_object_get_path_string (GST_OBJECT (obj));if (val != NULL) {if (G_VALUE_HOLDS_STRING (val))val_str = g_value_dup_string (val);else if (G_VALUE_TYPE (val) == GST_TYPE_CAPS)val_str = gst_caps_to_string (g_value_get_boxed (val));else if (G_VALUE_TYPE (val) == GST_TYPE_TAG_LIST)val_str = gst_tag_list_to_string (g_value_get_boxed (val));else if (G_VALUE_TYPE (val) == GST_TYPE_STRUCTURE)val_str = gst_structure_to_string (g_value_get_boxed (val));elseval_str = gst_value_serialize (val);} else {val_str = g_strdup ("(no value)");}gst_print ("%s: %s = %s\n", obj_name, name, val_str);g_free (obj_name);g_free (val_str);break;

同样的，在codec-select的代码中，有deep_notify信号回调函数gst_object_default_deep_notify：

gst-plugins-base/tests/examples/dynamic/codec-select.c

  g_signal_connect (pipeline, "deep_notify",G_CALLBACK (gst_object_default_deep_notify), NULL);

gst_object_default_deep_notify：

void
gst_object_default_deep_notify (GObject * object, GstObject * orig,GParamSpec * pspec, gchar ** excluded_props)
{GValue value = { 0, };        /* the important thing is that value.type = 0 */gchar *str = NULL;gchar *name = NULL;if (pspec->flags & G_PARAM_READABLE) {/* let's not print these out for excluded properties... */while (excluded_props != NULL && *excluded_props != NULL) {if (strcmp (pspec->name, *excluded_props) == 0)return;excluded_props++;}g_value_init (&value, pspec->value_type);g_object_get_property (G_OBJECT (orig), pspec->name, &value);if (G_VALUE_HOLDS_STRING (&value))str = g_value_dup_string (&value);elsestr = gst_value_serialize (&value);name = gst_object_get_path_string (orig);// 打印-v参数g_print ("%s: %s = %s\n", name, pspec->name, str);g_free (name);g_free (str);g_value_unset (&value);} else {name = gst_object_get_path_string (orig);g_warning ("Parameter %s not readable in %s.", pspec->name, name);g_free (name);}
}