mirrors/gstreamer
mirrors/gstreamer
1
1
Fork 0
mirror of https://gitlab.freedesktop.org/gstreamer/gstreamer.git synced 2024-06-20 23:10:40 +00:00
Code Issues 1 Projects Releases Wiki Activity

docs/pwg/advanced-tagging.xml: Add a part about tag reading and application signalling... Tag writing still needs to ...

Browse source 
Original commit message from CVS:
2004-01-29  Ronald Bultje  <rbultje@ronald.bitfreak.net>

* docs/pwg/advanced-tagging.xml:
Add a part about tag reading and application signalling... Tag
writing still needs to be documented.
* gst/elements/gstfilesrc.c: (gst_filesrc_set_location):
We can set file locations in READY, too.
This commit is contained in:
Ronald S. Bultje 2004-01-29 10:56:53 +00:00
parent 7e586c017f
commit 7d41ae65f4
4 changed files with 114 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
ChangeLog
View file

@ -1,3 +1,11 @@
2004-01-29 Ronald Bultje <rbultje@ronald.bitfreak.net>
* docs/pwg/advanced-tagging.xml:
Add a part about tag reading and application signalling... Tag
writing still needs to be documented.
* gst/elements/gstfilesrc.c: (gst_filesrc_set_location):
We can set file locations in READY, too.
2004-01-29 Julien MOUTTE <julien@moutte.net>
* docs/random/ds/element-checklist: Adding some notes about src

103
docs/pwg/advanced-tagging.xml
View file

@ -40,8 +40,109 @@
<sect1 id="section-tagging-read" xreflabel="Reading Tags from Streams">
<title>Reading Tags from Streams</title>
<para>
WRITEME
The basic object for tags is a <classname>GstTagList</classname>. An
element that is reading tags from a stream should create an empty taglist
and fill this with individual tags. Empty tag lists can be created with
<function>gst_tag_list_new ()</function>. Then, the element can fill the
list using <function>gst_tag_list_add_values ()</function>. Note that
an element probably reads metadata as strings, but values might not
necessarily be strings. Be sure to use <function>gst_value_transform ()</function>
to make sure that your data is of the right type. After data reading, the
application can be notified of the new taglist by calling
<function>gst_element_found_tags ()</function>. The tags should also be
part of the datastream, so they should be pushed over all source pads.
The function <function>gst_event_new_tag ()</function> creates an event
from a taglist. This can be pushed over source pads using
<function>gst_pad_push ()</function>. Simple elements with only one
source pad can combine all these steps all-in-one by using the function
<function>gst_element_found_tags_for_pad ()</function>.
</para>
<para>
The following example program will parse a file and parse the data as
metadata/tags rathen than as actual content-data. It will parse each
line as <quote>name:value</quote>, where name is the type of metadata
(title, author, ...) and value is the metadata value. The
<function>_getline ()</function> is the same as the one given in
<xref linkend="section-reqpad-sometimes"/>.
</para>
<programlisting>
static void
gst_my_filter_loopfunc (GstElement *element)
{
GstMyFilter *filter = GST_MY_FILTER (element);
GstBuffer *buf;
GstTagList *taglist = gst_tag_list_new ();
/* get each line and parse as metadata */
while ((buf = gst_my_filter_getline (filter))) {
gchar *line = GST_BUFFER_DATA (buf), *colon_pos, *type = NULL;a
/* get the position of the ':' and go beyond it */
if (!(colon_pos = strchr (line, ';')))
goto next:
/* get the string before that as type of metadata */
type = g_strndup (line, colon_pos - line);
/* content is one character beyond the ':' */
colon_pos = &amp;colon_pos[1];
if (*colon_pos == '\0')
goto next;
/* get the metadata category, it's value type, store it in that
* type and add it to the taglist. */
if (gst_tag_exists (type)) {
GValue from = { 0 }, to = { 0 };
GType to_type;
to_type = gst_tag_get_type (type);
g_value_init (&amp;from, G_TYPE_STRING);
g_value_set_string (&amp;from, colon_pos);
g_value_init (&amp;to, to_type);
g_value_transform (&amp;from, &amp;to);
g_value_unset (&amp;from);
gst_tag_list_add_values (taglist, GST_TAG_MERGE_APPEND,
type, &amp;to, NULL);
g_value_unset (&amp;to);
}
next:
g_free (type);
gst_buffer_unref (buf);
}
/* signal metadata */
gst_element_found_tags_for_pad (element, filter->srcpad, 0, taglist);
gst_tag_list_free (taglist);
/* send EOS */
gst_pad_send_event (filter->srcpad, GST_DATA (gst_event_new (GST_EVENT_EOS)));
gst_element_set_eos (element);
}
</programlisting>
<para>
We currently assume the core to already <emphasis>know</emphasis> the
mimetype (<function>gst_tag_exists ()</function>). You can add new tags
to the list of known tags using <function>gst_tag_register ()</function>.
If you think the tag will be useful in more cases than just your own
element, it might be a good idea to add it to <filename>gsttag.c</filename>
instead. That's up to you to decide. If you want to do it in your own
element, it's easiest to register the tag in one of your class init
functions, preferrably <function>_class_init ()</function>.
</para>
<programlisting>
static void
gst_my_filter_class_init (GstMyFilterClass *klass)
{
[..]
gst_tag_register ("my_tag_name", GST_TAG_FLAG_META,
G_TYPE_STRING,
_("my own tag"),
_("a tag that is specific to my own element"),
NULL);
[..]
}
</programlisting>
</sect1>
<sect1 id="section-tagging-write" xreflabel="Writing Tags to Streams">

3
gst/elements/gstfilesrc.c
View file

@ -257,7 +257,8 @@ static gboolean
gst_filesrc_set_location (GstFileSrc *src, const gchar *location)
{
/* the element must be stopped in order to do this */
if (GST_STATE (src) != GST_STATE_NULL)
if (GST_STATE (src) != GST_STATE_READY &&
GST_STATE (src) != GST_STATE_NULL)
return FALSE;
if (src->filename) g_free (src->filename);

3
plugins/elements/gstfilesrc.c
View file

@ -257,7 +257,8 @@ static gboolean
gst_filesrc_set_location (GstFileSrc *src, const gchar *location)
{
/* the element must be stopped in order to do this */
if (GST_STATE (src) != GST_STATE_NULL)
if (GST_STATE (src) != GST_STATE_READY &&
GST_STATE (src) != GST_STATE_NULL)
return FALSE;
if (src->filename) g_free (src->filename);