c++ - 更改 GStreamer 上的视频格式

Question

我正在尝试为我正在编写的应用程序在 gstreamer-1.0 上覆盖 .png 图像(带有 alpha channel )，但是，在大量搜索网络和阅读文档之后，我仍然对使用方法。

我使用的方法是:

filesrc -> pngdec -> imagefreeze -> videoconvert -> videoscale ->videomixer -> output_of_bininput_of_bin -> videoconvert -> videoscale ->|

这是一个较大应用程序的一小部分。

我的问题是设置 videoscale 和 videoconvert 元素的属性，我认为您应该使用 GSTCaps，但这不起作用。我试过很多方法。这是提供覆盖的类中的成员函数。对于代码的困惑，我深表歉意，但它是实验性的。

bool ImageOverlay::CreateElement()
{
  GstPad *source_pad, *sink_pad;
  GstElement *file_source, *png_decoder, *freeze, *colorspace,
      *video_mixer, *identity, * colorspace2, *video_scale_1, *video_scale_2;

  /* Create gstreamer elements */
  _image_overlay_element = gst_bin_new("image-player");

  if(!_image_overlay_element)
  {
    g_printerr ("Pipeline could not be created. Exiting.\n");
    return false;
  }

  // Create file source
  file_source = gst_element_factory_make ("multifilesrc",  "file-source");
  g_object_set (G_OBJECT (file_source), "location", "../Template1.png", NULL);

  if(!file_source)
  {
    g_printerr ("File could not be created. Exiting.\n");
    return false;
  }

  // Decode file
  png_decoder  = gst_element_factory_make ("pngdec", "png-decoder");
  if(!png_decoder)
  {
    g_printerr ("png-decoder could not be created. Exiting.\n");
    return false;
  }

  // Create colour space convertor
  colorspace = gst_element_factory_make("videoconvert", "colorspace");
  if(!colorspace)
  {
    g_printerr ("Colorspace could not be created. Exiting.\n");
    return false;
  }

  // Create colour space convertor
  colorspace2 = gst_element_factory_make("videoconvert", "colorspace2");
  if(!colorspace)
  {
    g_printerr ("Colorspace could not be created. Exiting.\n");
    return false;
  }

  // Create idenentiy component, does nothing but is useful for debug
  identity = gst_element_factory_make("identity", "identity");
  if(!identity)
  {
    g_printerr ("Colorspace could not be created. Exiting.\n");
    return false;
  }

  // Create a video mixer
  video_mixer = gst_element_factory_make("videomixer", "mixer");
  if(!video_mixer)
  {
    g_printerr ("videomixer could not be created. Exiting.\n");
    return false;
  }

  // Create a freeze element
  freeze = gst_element_factory_make("imagefreeze", "freeze");
  if(!freeze)
  {
    g_printerr ("ImageFreeze could not be created. Exiting.\n");
    return false;
  }

  video_scale_1 = gst_element_factory_make("videoscale", NULL);
  if(!video_scale_1)
  {
    g_printerr ("video_scale_1 could not be created. Exiting.\n");
    return false;
  }

  video_scale_2 = gst_element_factory_make("videoscale", NULL);
  if(!video_scale_2)
  {
    g_printerr ("video_scale_2 could not be created. Exiting.\n");
    return false;
  }

  // Add to the bin
  gst_bin_add_many (GST_BIN (_image_overlay_element),
                    file_source,
                    png_decoder,
                    colorspace,
                    colorspace2,
                    freeze,
                    video_mixer,
                    identity,
                    video_scale_1,
                    video_scale_2,
                    NULL);


  if (!gst_element_link_many (file_source, png_decoder, video_scale_1, freeze, NULL))
  {
    std::cout << "Could not link" << std::endl;
  }

  GstCaps * caps = gst_caps_new_simple ("video/x-raw",
                                        "format", G_TYPE_STRING, "ARGB",
                                        NULL);


  GstCaps * caps2 = gst_caps_new_simple("width", G_TYPE_INT, 640,
                                        "height", G_TYPE_INT, 480,
                                        NULL);

  gst_element_link_filtered(video_scale_1, freeze, caps2);
  gst_element_link_filtered(video_scale_2, freeze, caps2);

  if (!gst_element_link_many(freeze, video_scale_2, colorspace, NULL))
  {
    std::cout << "Could not link" << std::endl;
  }

  // Link pads to video mixer
  GstPad * sink_pad_1 = gst_element_get_request_pad (video_mixer, "sink_%u");
  GstPad * sink_pad_2 = gst_element_get_request_pad (video_mixer, "sink_%u");
  GstPad * source_2 = gst_element_get_static_pad (identity, "src");
  GstPad * source_1 = gst_element_get_static_pad (colorspace, "src");

  gst_pad_set_caps(source_2, caps);
  gst_pad_set_caps(source_1, caps);
  gst_caps_unref(caps);

  if (!gst_pad_link ( source_1, sink_pad_1) == GST_PAD_LINK_OK)
  {
    std::cout << "Could not link pads" << std::endl;
    return false;
  }

  if (!gst_pad_link ( source_2, sink_pad_2) == GST_PAD_LINK_OK)
  {
    std::cout << "Could not link pads" << std::endl;
    return false;
  }

  gst_pad_set_active(source_1, true);
  gst_pad_set_active(sink_pad_1, true);
  gst_pad_set_active(source_2, true);
  gst_pad_set_active(sink_pad_2, true);

  // Add pad to this element
  source_pad = gst_element_get_static_pad (video_mixer, "src");
  sink_pad = gst_element_get_static_pad(identity, "sink");
  gst_element_add_pad (_image_overlay_element, gst_ghost_pad_new ("src", source_pad));
  gst_element_add_pad (_image_overlay_element, gst_ghost_pad_new ("sink", sink_pad));

  return true;
}

我想将两个源调整为相同大小，并将 png 图像覆盖在视频上。该 block 主要起作用，但我无法使调整大小或 alpha channel 的东西起作用。

谢谢，

编辑:

我现在已经修改了我的代码并且有了更好的理解，但是，问题似乎在于，如果 capfilter 使用 RGBA，则它不会链接，其他一些格式可以工作但没有用。我不知道为什么。

bool ImageOverlay::MakeElements()
{
  try
  {
    // Creates the bin at this level
    CreatePipeline();
    GstElement *file_source, *png_decoder, *freeze, *colorspace,
        *video_mixer, *identity, * colorspace2, *video_scale_1, *video_scale_2, *caps_filter1, *caps_filter2;

    // Create elements
    file_source = CreateElementAndAddToBin("multifilesrc",  "file-source");
    png_decoder   = CreateElementAndAddToBin("pngdec", "png-decoder");
    colorspace    = CreateElementAndAddToBin("videoconvert", "colorspace");
    colorspace2   = CreateElementAndAddToBin("videoconvert", "colorspace2");
    identity      = CreateElementAndAddToBin("identity", "identity");
    video_mixer   = CreateElementAndAddToBin("videomixer", "mixer");
    freeze        = CreateElementAndAddToBin("imagefreeze", "freeze");
    video_scale_1 = CreateElementAndAddToBin("videoscale", "scale1");
    video_scale_2 = CreateElementAndAddToBin("videoscale", "scale2");
    caps_filter1  = CreateElementAndAddToBin("capsfilter", "caps_filter1");
    caps_filter2  = CreateElementAndAddToBin("capsfilter", "caps_filter2");

    // Set input file
    g_object_set (G_OBJECT (file_source), "location", "../Template1.png", NULL);

    // Create caps
    GstCaps *caps = gst_caps_new_simple ("video/x-raw",
                                         "format", G_TYPE_STRING, "YV12", //<<< IF THIS IS SET TO ARGB (THE FORMAT I WANT IT FAILS ON LINKING)
                                         "framerate", GST_TYPE_FRACTION, 25, 1,
                                         "pixel-aspect-ratio", GST_TYPE_FRACTION, 1, 1,
                                         "width", G_TYPE_INT, 640,
                                         "height", G_TYPE_INT, 480,
                                         NULL);


    // Set caps on cap filter
    g_object_set(G_OBJECT(caps_filter2), "caps", caps, NULL);
    g_object_set(G_OBJECT(caps_filter1), "caps", caps, NULL);


    // Link up elements
    if (!gst_element_link_many (identity, video_scale_2, colorspace2, caps_filter2, video_mixer, NULL))
    {
      std::cout << "Could not link input branch" << std::endl;  //<<<< IF ARGB OR OTHER FORMATS SUCH AS RGBA ARE USED
    }                                                           // IN CAP FILTER, THIS FAILS, SAME WITH BELOW. IT WORKS WITH YV12!

    if (!gst_element_link_many (file_source, png_decoder, freeze, video_scale_1, colorspace, caps_filter1, video_mixer, NULL))
    {
      std::cout << "Could not link image source branch" << std::endl;
    }

    // Add ghost pads to this bin, allowing it to be used as an element
    SetInputElement(identity);
    SetOutputElement(video_mixer);
  }
  catch(...)
  {
    std::cout << "Overlay generator failed to build, exception thrown" << std::endl;

    // TODO - Clear up in here
    return false;
  }

  return true;
}

Answer 1

从 gstreamer 1.2 开始，视频转换由混音器承担，如果其中一个接收器垫具有 alpha，它将自动选择一种 alpha 格式。

如果您可以更新到 1.2，您需要使用的管道将具有以下形式:

gst-launch-1.0 uridecodebin uri=file:///home/meh/Pictures/pitivi/nicetext.png ! imagefreeze ! videomixer name=m sink_0::zorder=0 ! videoconvert ! autovideosink videotestsrc ! videoscale ! video/x-raw, width=640, height=400 ! m.

其中 nicetext.png 是一个 (png) 640 x 400 图像文件，具有透明背景和一些随机文本。

videoscale 之后的部分是一个 capsfilter，你可以通过以下方式创建它:

gst_element_factory_make("capsfilter", "random_name")

然后将其 caps 属性设置为您需要的宽度和高度。如果事先不知道这一点，您将需要在焊盘上设置一个焊盘探针，您需要从中复制宽度和高度、拦截 caps 事件并在此时将 caps 设置在 capsfilter 上。

如果由于某种原因您不能使用 1.2，那么您将需要在两个分支上使用 videoconvert 和 capsfilter，并指定您需要的格式。