我正在尝试在 gstreamer-1.0 上为我正在编写的应用程序覆盖 .png 图像（带有 alpha 通道），但是，经过大量搜索网络和阅读文档后，我仍然对这种方法感到有些困惑利用。
我使用的方法是：
filesrc -> pngdec -> imagefreeze -> videoconvert -> videoscale -> videomixer -> output_of_bin input_of_bin -> videoconvert -> videoscale ->|
这是较大应用程序的一小部分。
我的问题是在 videoscale 和 videoconvert 元素上设置属性，我认为您应该使用 GSTCaps，但这不起作用。我尝试了很多方法。这是提供覆盖的类中的成员函数。我为代码的混乱提前道歉，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;
}
我想将两个来源调整为相同的大小并将 png 图像覆盖在视频上。该块主要工作，但我无法让调整大小或 alpha 通道的东西工作。
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，问题似乎是如果 capfilter 使用 RGBA 将不会链接，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;
}