c++ - gstreamer:如何更改网络摄像头的输入/输出分辨率？

Question

我想使用 gstreamer 更改网络摄像头的输出/输入分辨率。例如，我想将结果从 800x600 像素更改为 640x480 像素。我在 C 中找不到执行此操作的语法。谁能帮帮我？

此代码应显示来自网络摄像头的视频流:

#include <gst/gst.h>

int main(int argc, char *argv[]) {
    GstElement *pipeline, *source, *sink, *convert;
    GstBus *bus;
    GstMessage *msg;
    GstStateChangeReturn ret;

    /* Initialize GStreamer */
    gst_init (&argc, &argv);

    /* Create the elements */
    source = gst_element_factory_make ("v4l2src", "source");
    sink = gst_element_factory_make ("autovideosink", "sink");
    convert =gst_element_factory_make("ffmpegcolorspace","convert");

    /* Create the empty pipeline */
    pipeline = gst_pipeline_new ("test-pipeline");

    if (!pipeline || !source || !sink || !convert) {
        g_printerr ("Not all elements could be created.\n");
        return -1;
    }

    /*set der source*/
    g_object_set (source, "device", "/dev/video0", NULL);

    /* Build the pipeline */
    gst_bin_add_many (GST_BIN (pipeline), source, sink, convert, NULL);
    if (gst_element_link (convert, sink) != TRUE) {
        g_printerr ("Elements could not be linked confert sink.\n");
        gst_object_unref (pipeline);
        return -1;
    }


    if (gst_element_link (source, convert) != TRUE) {
        g_printerr ("Elements could not be linked source -convert.\n");
        gst_object_unref (pipeline);
        return -1;
    }

    /* Start playing */
    ret = gst_element_set_state (pipeline, GST_STATE_PLAYING);
    if (ret == GST_STATE_CHANGE_FAILURE) {
        g_printerr ("Unable to set the pipeline to the playing state.\n");
        gst_object_unref (pipeline);
        return -1;
    }

    /* Wait until error or EOS */
    bus = gst_element_get_bus (pipeline);
    msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE, GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

    /* Parse message */
    if (msg != NULL) {
        GError *err;
        gchar *debug_info;

        switch (GST_MESSAGE_TYPE (msg)) {
            case GST_MESSAGE_ERROR:
                gst_message_parse_error (msg, &err, &debug_info);
                g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);
                g_printerr ("Debugging information: %s\n", debug_info ? debug_info : "none");
                g_clear_error (&err);
                g_free (debug_info);
                break;
            case GST_MESSAGE_EOS:
                g_print ("End-Of-Stream reached.\n");
                break;
            default:
                /* We should not reach here because we only asked for ERRORs and EOS */
                g_printerr ("Unexpected message received.\n");
                break;
        }
        gst_message_unref (msg);
    }

    /* Free resources */
    gst_object_unref (bus);
    gst_element_set_state (pipeline, GST_STATE_NULL);
    gst_object_unref (pipeline);
    return 0;
}

Answer 1

谢谢你，你救了我的命。无论如何，我拼命地找到一个代码来使用 C++ 代码捕获 video0。你的问题解决了吗？？希望这个附件能帮到你

static gboolean initialize_pipeline(AppData *appdata,
    int *argc, char ***argv)
{
GstElement *pipeline, *camera_src, *screen_sink, *image_sink;
GstElement *screen_queue, *image_queue;
GstElement *csp_filter, *image_filter, *tee;
GstCaps *caps;
GstBus *bus;


/* Initialize Gstreamer */
gst_init(argc, argv);

/* Create pipeline and attach a callback to it's
 * message bus */
pipeline = gst_pipeline_new("test-camera");

bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline));
gst_bus_add_watch(bus, (GstBusFunc)bus_callback, appdata);
gst_object_unref(GST_OBJECT(bus));

/* Save pipeline to the AppData structure */
appdata->pipeline = pipeline;

/* Create elements */
/* Camera video stream comes from a Video4Linux driver */
camera_src = gst_element_factory_make(VIDEO_SRC, "camera_src");
/* Colorspace filter is needed to make sure that sinks understands
 * the stream coming from the camera */
csp_filter = gst_element_factory_make("ffmpegcolorspace", "csp_filter");
/* Tee that copies the stream to multiple outputs */
tee = gst_element_factory_make("tee", "tee");
/* Queue creates new thread for the stream */
screen_queue = gst_element_factory_make("queue", "screen_queue");
/* Sink that shows the image on screen. Xephyr doesn't support XVideo
 * extension, so it needs to use ximagesink, but the device uses
 * xvimagesink */
screen_sink = gst_element_factory_make(VIDEO_SINK, "screen_sink");
/* Creates separate thread for the stream from which the image
 * is captured */
image_queue = gst_element_factory_make("queue", "image_queue");
/* Filter to convert stream to use format that the gdkpixbuf library
 * can use */
image_filter = gst_element_factory_make("ffmpegcolorspace", "image_filter");
/* A dummy sink for the image stream. Goes to bitheaven */
image_sink = gst_element_factory_make("fakesink", "image_sink");

/* Check that elements are correctly initialized */
if(!(pipeline && camera_src && screen_sink && csp_filter && screen_queue
    && image_queue && image_filter && image_sink))
{
    g_critical("Couldn't create pipeline elements");
    return FALSE;
}

/* Set image sink to emit handoff-signal before throwing away
 * it's buffer */
g_object_set(G_OBJECT(image_sink),
        "signal-handoffs", TRUE, NULL);

/* Add elements to the pipeline. This has to be done prior to
 * linking them */
gst_bin_add_many(GST_BIN(pipeline), camera_src, csp_filter,
        tee, screen_queue, screen_sink, image_queue,
        image_filter, image_sink, NULL);

/* Specify what kind of video is wanted from the camera */
caps = gst_caps_new_simple("video/x-raw-rgb",
        "width", G_TYPE_INT, 640,
        "height", G_TYPE_INT, 480,
        NULL);


/* Link the camera source and colorspace filter using capabilities
 * specified */
if(!gst_element_link_filtered(camera_src, csp_filter, caps))
{
    return FALSE;
}
gst_caps_unref(caps);

/* Connect Colorspace Filter -> Tee -> Screen Queue -> Screen Sink
 * This finalizes the initialization of the screen-part of the pipeline */
if(!gst_element_link_many(csp_filter, tee, screen_queue, screen_sink, NULL))
{
    return FALSE;
}

/* gdkpixbuf requires 8 bits per sample which is 24 bits per
 * pixel */
caps = gst_caps_new_simple("video/x-raw-rgb",
        "width", G_TYPE_INT, 640,
        "height", G_TYPE_INT, 480,
        "bpp", G_TYPE_INT, 24,
        "depth", G_TYPE_INT, 24,
        "framerate", GST_TYPE_FRACTION, 15, 1,
        NULL);

/* Link the image-branch of the pipeline. The pipeline is
 * ready after this */
if(!gst_element_link_many(tee, image_queue, image_filter, NULL)) return FALSE;
if(!gst_element_link_filtered(image_filter, image_sink, caps)) return FALSE;

gst_caps_unref(caps);

/* As soon as screen is exposed, window ID will be advised to the sink */
g_signal_connect(appdata->screen, "expose-event", G_CALLBACK(expose_cb),
         screen_sink);

gst_element_set_state(pipeline, GST_STATE_PLAYING);

return TRUE;

谢谢。