Load properties from a JSON file created by tcam capture

tiscamera 1.0 / 1.1

tcam-capture can save the current property values into a JSON file.

• Start tcam-capture and select your video capture device.
• Click on "Properties" menu and configure the properties to your needs.
• Click on "Info" menu. Choose the "State" tab in the information dialog
• Click on "Save" and save the properties in a file.
• Close tcam-capture.

Create a usual C++ project, maybe copy and paste the code from tiscamera/examples/c/03-live-stream.c as basic code.

Include this:

#include <iostream>
#include <fstream>
#include <streambuf>

It is used for reading the created json file. The json file is not interpreted as JSON file. It is read simply into a string. Therefore, no JSON library is necessary.

Now do the GStreamer code:

    const char* serial = "41910044"; // Replace with the serial number of your device.

    GError* err = NULL;

    GstElement* pipeline =
        gst_parse_launch("tcambin name=source ! video/x-raw,format=BGRx ! videoconvert ! ximagesink", &err);

    if (err)
    {
        std::cout << err->message << std::endl;
        g_error_free(err);
        err = NULL;
        return 1;
    }

    /* test for error */
    if (pipeline == NULL)
    {
        printf("Could not create pipeline. Cause: %s\n", err->message);
        return 1;
    }

    GstElement* tcambin = gst_bin_get_by_name(GST_BIN(pipeline), "source");
    if (serial != NULL)
    {
        GValue val = {};
        g_value_init(&val, G_TYPE_STRING);
        g_value_set_static_string(&val, serial);

        g_object_set_property(G_OBJECT(tcambin), "serial", &val);

    }
    // Set the pipeline in state ready, so we can set properties
    gst_element_set_state(pipeline, GST_STATE_READY);
    gst_element_get_state(pipeline, NULL, NULL, 4000000000ll);

The code queries the tcambin (GstElement *) from the pipeline (in the 03-live-stream it was named "source"). The serial number is passed to the tcambin. After that, the pipeline is set into READY state.

Read the json file saved by tcam-capture. We assume, it was named "properties.json" and is saved in our current working directory:

   // Read the file "properties.json" created by tcam-capture.
    std::ifstream t("properties.json");
    std::string jsonproperties((std::istreambuf_iterator<char>(t)),
                 std::istreambuf_iterator<char>());

    // Create a GValue of type string and pass the content of
    // jsonpropties to it
    GValue val = {};
    g_value_init(&val, G_TYPE_STRING);
    g_value_set_static_string(&val, jsonproperties.c_str());

    // Now pass the properties to the tcambin. 
    g_object_set_property(G_OBJECT(tcambin), "tcam-properties-json", &val);

    // tcambin is no longer needed, so unref it here.
    gst_object_unref(tcambin);

The tcam-properties-json property of tcambin is set with the content of the json file.

That is all.

Complete code:

#include <iostream>
#include <fstream>
#include <streambuf>
#include <gst/gst.h>

int main(int argc, char** argv)
{
    gst_init( &argc,&argv);
    std::cout << "Template execuable" << std::endl;

    const char* serial = "41910044"; // set this if you do not want the first found device

    GError* err = NULL;

    GstElement* pipeline =
        gst_parse_launch("tcambin name=source ! video/x-raw,format=BGRx ! videoconvert ! ximagesink", &err);

    if (err)
    {
        std::cout << err->message << std::endl;
        g_error_free(err);
        err = NULL;
        return 1;
    }

    /* test for error */
    if (pipeline == NULL)
    {
        printf("Could not create pipeline. Cause: %s\n", err->message);
        return 1;
    }

    GstElement* tcambin = gst_bin_get_by_name(GST_BIN(pipeline), "source");
    if (serial != NULL)
    {
        GValue val = {};
        g_value_init(&val, G_TYPE_STRING);
        g_value_set_static_string(&val, serial);

        g_object_set_property(G_OBJECT(tcambin), "serial", &val);

    }

    // Set the pipeline in state ready, so we can set properties
    gst_element_set_state(pipeline, GST_STATE_READY);
    gst_element_get_state(pipeline, NULL, NULL, 4000000000ll);

    
    // Read the file "properties.json" created by tcam-capture.
    std::ifstream t("properties.json");
    std::string jsonproperties((std::istreambuf_iterator<char>(t)),
                 std::istreambuf_iterator<char>());

    // Create a GValue of type string and pass the content of
    // jsonpropties to it
    GValue val = {};
    g_value_init(&val, G_TYPE_STRING);
    g_value_set_static_string(&val, jsonproperties.c_str());

    // Now pass the properties to the tcambin. 
    g_object_set_property(G_OBJECT(tcambin), "tcam-properties-json", &val);

    // tcambin is no longer needed, so unref it here.
    gst_object_unref(tcambin);

    
    // Start the pipelnie
    gst_element_set_state(pipeline, GST_STATE_PLAYING);
    gst_element_get_state(pipeline, NULL, NULL, 4000000000ll);

    std::cout << "Press enter to stop the stream." << std::endl;
    getchar();

    gst_element_set_state(pipeline, GST_STATE_NULL);
    gst_element_get_state(pipeline, NULL, NULL, 4000000000ll);

    gst_object_unref(pipeline);

    return 0;
}