Images Slideshow in Gstreamer

I want to make a GStreamer application which takes a xml file process its content which provides information like image url, its weight and the duration for which it is going to be displayed on the screen.

The xml file can be clearly processed in C using libxml. But how can we create a slideshow of the images using the GStreamer libraries. I want to use GStreamer because the hardware and the SDK I am using provide native support for GStreamer.

Are there any GStreamer plugins to do the same. Or how else can be done. I know GStreamer basics and can write code in C for GStreamer application.

回答1:

Try the following piece of code of C :

#include <gst/gst.h>
#include <glib.h>

char *strcpy(char *dest, const xmlChar *src)
{
    unsigned i;
    for (i=0; src[i] != '\0'; ++i)
    dest[i] = src[i];
        dest[i] = '\0';
    return dest;
}


int main (int   argc, char *argv[])

{
char *docname;
char *image1 = malloc(1000);
char *image2 = malloc(1000);

docname = "input.xml";

//parse the document
xmlDocPtr doc;
xmlNodePtr cur1, cur2, cur3;

doc = xmlParseFile(docname);

if (doc == NULL ) {
    fprintf(stderr,"Document not parsed successfully. \n");
    return -1;
}

cur1 = xmlDocGetRootElement(doc);

if (cur1 == NULL) {
    fprintf(stderr,"Empty Document\n");
    xmlFreeDoc(doc);
    return -1;
}

if (xmlStrcmp(cur1->name, (const xmlChar *) "start")) {
    fprintf(stderr,"document of the wrong type, root node is supposed to be start");
    xmlFreeDoc(doc);
    return -1;
}

int flag=0;
cur2 = cur1->xmlChildrenNode;
while (cur2 != NULL)
{
    if ((!xmlStrcmp(cur2->name, (const xmlChar *)"image")))
    {
        //parseVideo (doc, cur2);
        xmlChar *key;
        cur3 = cur2->xmlChildrenNode;
        while (cur3 != NULL) 
        {
            if ((!xmlStrcmp(cur3->name, (const xmlChar *)"filename"))) 
            {
                key = xmlNodeListGetString(doc, cur3->xmlChildrenNode, 1);
                //printf("Name of the file is: %s\n", key);
                xmlFree(key);
            }

            if ((!xmlStrcmp(cur3->name, (const xmlChar *)"src"))) 
            {
                key = xmlNodeListGetString(doc, cur3->xmlChildrenNode, 1);
                if (flag == 1)
                {
                        strcpy(image2, key);
                        printf("the image 2 is %s \n", image2);
                        flag = 2;
                }
                if(flag == 0)
                {
                        strcpy(image1, key);
                        printf("the image 1 is %s \n", image1);
                        flag = 1;
                }
                    //printf("SRC of the file is: %s\n", key);
                xmlFree(key);
            }

            if ((!xmlStrcmp(cur3->name, (const xmlChar *)"duration"))) 
            {
                key = xmlNodeListGetString(doc, cur3->xmlChildrenNode, 1);
                //printf("No. of seconds the image should be displayed is: %s\n", key);
                xmlFree(key);
            }

            if ((!xmlStrcmp(cur3->name, (const xmlChar *)"weight"))) 
            {
                key = xmlNodeListGetString(doc, cur3->xmlChildrenNode, 1);
                //printf("The weight of the image is: %s\n", key);
                xmlFree(key);
            }
        cur3 = cur3->next;
        }
    }
cur2 = cur2->next;
}

xmlFreeDoc(doc);

GstElement *pipeline, *source, *jpg_decoder, *freeze, *colorspace, *sink;

  /* Initialisation */
gst_init (&argc, &argv);

/* Create gstreamer elements */
pipeline = gst_pipeline_new ("image-player");
if(!pipeline)
{
    g_printerr ("Pipeline could not be created. Exiting.\n");
    return -1;
}

  source   = gst_element_factory_make ("filesrc",       "file-source");
  //set the location of the file to the argv[1]
  g_object_set (G_OBJECT (source), "location", image1, NULL);
if(!source)
{
    g_printerr ("File could not be created. Exiting.\n");
    return -1;
}

jpg_decoder  = gst_element_factory_make ("jpegdec", "jpg-decoder");
if(!jpg_decoder)
{
    g_printerr ("Jpg Decoder could not be created. Exiting.\n");
    return -1;
}  

freeze = gst_element_factory_make("imagefreeze", "freeze");
if(!freeze)
{
    g_printerr ("ImageFreeze could not be created. Exiting.\n");
    return -1;
}  

colorspace = gst_element_factory_make("ffmpegcolorspace", "colorspace");
if(!colorspace)
{
    g_printerr ("Colorspace could not be created. Exiting.\n");
    return -1;
}  

sink     = gst_element_factory_make ("ximagesink", "imagesink");
if(!sink)
{
    g_printerr ("Image sink could not be created. Exiting.\n");
    return -1;
}

/* file-source | jpg-decoder | image-freeze | colorspace | sink */
gst_bin_add_many (GST_BIN (pipeline), source, jpg_decoder, freeze, colorspace, sink, NULL);
gst_element_link_many (source, jpg_decoder, freeze, colorspace, sink, NULL);

/* Set the pipeline to "playing" state*/
g_print ("Now playing: %s\n", image1);
gst_element_set_state (pipeline, GST_STATE_PLAYING);

getchar();
gst_element_set_state (pipeline, GST_STATE_READY);
g_object_set (G_OBJECT (source), "location", image2, NULL);
gst_element_set_state (pipeline, GST_STATE_PLAYING);
getchar();

/* Out of the main loop, clean up nicely */
g_print ("Returned, stopping playback\n");
gst_element_set_state (pipeline, GST_STATE_NULL);

g_print ("Deleting pipeline\n");
gst_object_unref (GST_OBJECT (pipeline));

    return 0;
}

回答2:

You have to create a pipeline with an imagefreeze element and change the source location when the image must be changed.

An example application (in Python) that shows two still images from hard disk:

import pygst
pygst.require("0.10")
import gst

player = gst.Pipeline("player")
source = gst.element_factory_make("filesrc", "file-source")
source.set_property("location", "image1.jpeg")
jpg_decoder = gst.element_factory_make("jpegdec", "jpg-decoder")
freeze = gst.element_factory_make("imagefreeze", "freeze")
colorspace = gst.element_factory_make("ffmpegcolorspace", "colorspace")
sink = gst.element_factory_make("ximagesink", "imagesink")

player.add(source, jpg_decoder, freeze, colorspace, sink)
gst.element_link_many(source, jpg_decoder, freeze, colorspace, sink)
player.set_state(gst.STATE_PLAYING)

inp = raw_input("Press enter:")
player.set_state(gst.STATE_READY)
source.set_property("location", "image2.jpeg")
player.set_state(gst.STATE_PLAYING)
inp = raw_input("Press enter again:")