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manual: add minimal tag reading example

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Should probably put that into tests/examples and figure out how to
get it included automatically, but can't be bothered right now.
This commit is contained in:
Tim-Philipp Müller 2010-05-02 19:30:30 +01:00
parent 3d6d9ca4e1
commit 77120a04a5
1 changed files with 107 additions and 0 deletions
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107
docs/manual/advanced-metadata.xml
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@ -42,6 +42,113 @@
merging mode, so that a new title (which came in later) has a
preference over the old one for display.
</para>
<para>
The following example will extract tags from a file and print them:
</para>
<programlisting>
/* compile with:
* gcc -o tags tags.c `pkg-config --cflags --libs gstreamer-0.10` */
#include &lt;gst/gst.h&gt;
static void
print_one_tag (const GstTagList * list, const gchar * tag, gpointer user_data)
{
int i, num;
num = gst_tag_list_get_tag_size (list, tag);
for (i = 0; i &lt; num; ++i) {
const GValue *val;
/* Note: when looking for specific tags, use the g_tag_list_get_xyz() API,
* we only use the GValue approach here because it is more generic */
val = gst_tag_list_get_value_index (list, tag, i);
if (G_VALUE_HOLDS_STRING (val)) {
g_print ("\t%20s : %s\n", tag, g_value_get_string (val));
} else if (G_VALUE_HOLDS_UINT (val)) {
g_print ("\t%20s : %u\n", tag, g_value_get_uint (val));
} else if (G_VALUE_HOLDS_DOUBLE (val)) {
g_print ("\t%20s : %g\n", tag, g_value_get_double (val));
} else if (G_VALUE_HOLDS_BOOLEAN (val)) {
g_print ("\t%20s : %s\n", tag,
(g_value_get_boolean (val)) ? "true" : "false");
} else if (GST_VALUE_HOLDS_BUFFER (val)) {
g_print ("\t%20s : buffer of size %u\n", tag,
GST_BUFFER_SIZE (gst_value_get_buffer (val)));
} else if (GST_VALUE_HOLDS_DATE (val)) {
g_print ("\t%20s : date (year=%u,...)\n", tag,
g_date_get_year (gst_value_get_date (val)));
} else {
g_print ("\t%20s : tag of type '%s'\n", tag, G_VALUE_TYPE_NAME (val));
}
}
}
static void
on_new_pad (GstElement * dec, GstPad * pad, GstElement * fakesink)
{
GstPad *sinkpad;
sinkpad = gst_element_get_static_pad (fakesink, "sink");
if (!gst_pad_is_linked (sinkpad)) {
if (gst_pad_link (pad, sinkpad) != GST_PAD_LINK_OK)
g_error ("Failed to link pads!");
}
gst_object_unref (sinkpad);
}
int
main (int argc, char ** argv)
{
GstElement *pipe, *dec, *sink;
GstMessage *msg;
gst_init (&amp;argc, &amp;argv);
if (argc &lt; 2 || !gst_uri_is_valid (argv[1]))
g_error ("Usage: %s file:///path/to/file", argv[0]);
pipe = gst_pipeline_new ("pipeline");
dec = gst_element_factory_make ("uridecodebin", NULL);
g_object_set (dec, "uri", argv[1], NULL);
gst_bin_add (GST_BIN (pipe), dec);
sink = gst_element_factory_make ("fakesink", NULL);
gst_bin_add (GST_BIN (pipe), sink);
g_signal_connect (dec, "pad-added", G_CALLBACK (on_new_pad), sink);
gst_element_set_state (pipe, GST_STATE_PAUSED);
while (TRUE) {
GstTagList *tags = NULL;
msg = gst_bus_timed_pop_filtered (GST_ELEMENT_BUS (pipe),
GST_CLOCK_TIME_NONE,
GST_MESSAGE_ASYNC_DONE | GST_MESSAGE_TAG | GST_MESSAGE_ERROR);
if (GST_MESSAGE_TYPE (msg) != GST_MESSAGE_TAG) /* error or async_done */
break;
gst_message_parse_tag (msg, &amp;tags);
g_print ("Got tags from element %s:\n", GST_OBJECT_NAME (msg-&gt;src));
gst_tag_list_foreach (tags, print_one_tag, NULL);
g_print ("\n");
gst_tag_list_free (tags);
gst_message_unref (msg);
};
if (GST_MESSAGE_TYPE (msg) == GST_MESSAGE_ERROR)
g_error ("Got error");
gst_message_unref (msg);
gst_element_set_state (pipe, GST_STATE_NULL);
gst_object_unref (pipe);
return 0;
}
</programlisting>
</sect1>
<sect1 id="section-tags-write">