docs: generate vaapijpegdec documentation

https://bugzilla.gnome.org/show_bug.cgi?id=764314

docs/plugins/gstreamer-vaapi-plugins-docs.xml.in

@@ -12,6 +12,7 @@
   <chapter>
     <title>gstreamer-vaapi Elements</title>
     <xi:include href="xml/element-vaapidecode.xml"/>
+    <xi:include href="xml/element-vaapijpegdec.xml"/>
     <xi:include href="xml/element-vaapidecodebin.xml"/>
     <xi:include href="xml/element-vaapipostproc.xml"/>
     <xi:include href="xml/element-vaapisink.xml"/>

docs/plugins/gstreamer-vaapi-plugins-sections.txt

@@ -2,15 +2,16 @@
 <FILE>element-vaapidecode</FILE>
 <TITLE>vaapidecode</TITLE>
 <SUBSECTION Standard>
-GST_IS_VAAPIDECODE
-GST_IS_VAAPIDECODE_CLASS
-GST_TYPE_VAAPIDECODE
-GST_VAAPIDECODE
-GST_VAAPIDECODE_CLASS
-GST_VAAPIDECODE_GET_CLASS
 GstVaapiDecode
 GstVaapiDecodeClass
-gst_vaapidecode_get_type
+</SECTION>
+
+<SECTION>
+<FILE>element-vaapijpegdec</FILE>
+<TITLE>vaapijpegdec</TITLE>
+<SUBSECTION Standard>
+GstVaapiDecode_jpeg
+GstVaapiDecode_jpegClass
 </SECTION>
 
 <SECTION>

gst/vaapi/gstvaapidecode.c

@@ -47,6 +47,31 @@
  * </refsect2>
  */
 
+/**
+ * SECTION:element-vaapijpegdec
+ * @short_description: A VA-API based JPEG image decoder
+ *
+ * vaapijpegdec decodes a JPEG image to surfaces suitable for the
+ * vaapisink or vaapipostproc elements using the installed <ulink
+ * url="https://wiki.freedesktop.org/www/Software/vaapi/">VA-API</ulink>
+ * back-end.
+ *
+ * In the case of OpenGL based elements, the buffers have the
+ * #GstVideoGLTextureUploadMeta meta, which efficiently copies the
+ * content of the VA-API surface into a GL texture.
+ *
+ * Also it can deliver normal video buffers that can be rendered or
+ * processed by other elements, but the performance would be rather
+ * bad.
+ *
+ * <refsect2>
+ * <title>Example launch line</title>
+ * |[
+ * gst-launch-1.0 filesrc location=~/image.jpeg ! jpegparse ! vaapijpegdec ! imagefreeze ! vaapisink
+ * ]|
+ * </refsect2>
+ */
+
 #include "gstcompat.h"
 #include <gst/vaapi/gstvaapidisplay.h>