Question

我想创建一个GStreamer应用程序，它接受一个xml文件处理其内容，该内容提供图像网址，重量和将在屏幕上显示的持续时间等信息。

可以使用libxml在C中清楚地处理xml文件。但是我们如何使用GStreamer库创建图像幻灯片。我想使用GStreamer，因为我使用的硬件和SDK为GStreamer提供原生支持。

是否有任何GStreamer插件可以做同样的事情。或者如何做到这一点。我知道GStreamer的基础知识，可以用C语言为GStreamer应用程序编写代码。

Answer 1

您必须使用imagefreeze元素创建管道，并在必须更改图像时更改源位置。

示例应用程序（在Python中），显示来自硬盘的两个静止图像：

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:")

Answer 2

尝试以下C代码：

#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;
}

Gstreamer中的图像幻灯片

2 个答案: