如何在 C 代码中实现 GStreamer tee

Question

我有以下工作流水线。它已经使用命令行工具 gst-launch-1.0 和函数 gst_parse_launch() 进行了测试，并且在这两种情况下都有效。

videotestsrc  ! video/x-raw,width=640,height=480 ! videocrop left=80 right=80 ! tee name=t ! queue ! glupload ! glimagesink t. ! queue ! jpegenc ! avimux ! filesink location=output.avi

我尝试在代码中手动设置它，但我现在遇到以下错误（应用程序打开，但没有显示视频）：

Error received from element videotestsrc0 : Internal data flow error.

Debugging information: gstbasesrc.c(2948): gst_base_src_loop (): /GstPipeline:pipeline0/GstVideoTestSrc:videotestsrc0: streaming task paused, reason not-negotiated (-4)

我在 Qt 应用程序中使用 GStreamer，glimagesink 将视频链接到 QML 类型。所有与 GStreamer 相关的代码都位于一个名为 GStreamer 的 GStreamer class 中。整个 cpp 文件发布在下面，以防问题出在我猜不到的地方。对于不相关的代码，我深表歉意。

static gboolean busCallback(GstBus *bus, GstMessage *message, gpointer data);

GStreamer::GStreamer(QQuickItem *parent) : QQuickItem(parent)
{
    qDebug() << "Constructed GSteamer";        
}    

void GStreamer::createPipeline()
{
    qDebug() << "Creating pipeline";      

    if(m_source.isEmpty()){
        qDebug() << "Error: Missing source property for GStreamer component";
        return;
    }

    if(m_videoItem.isEmpty()){
        qDebug() << "Error: Missing videoItem property for GStreamer component";
        return;
    }

    m_pipeline = gst_pipeline_new(NULL);
    m_sink = NULL;

    QByteArray ba = m_source.toLatin1();
    m_src = gst_element_factory_make(ba.data(), NULL);
    g_assert(m_src);


    m_filter = gst_element_factory_make("capsfilter", "filter");
    g_assert(m_filter);

    g_object_set(G_OBJECT (m_filter), "caps", gst_caps_new_simple("video/x-raw", 
        "width", G_TYPE_INT, 640,
        "height", G_TYPE_INT, 480,
        NULL), 
    NULL);

    m_convert = gst_element_factory_make("videoconvert", NULL);
    g_assert(m_convert);

    m_crop = gst_element_factory_make("videocrop", "crop");
    g_assert(m_crop);

    g_object_set(G_OBJECT (m_crop), "left", 80, "right", 80, NULL);

    // Tee
    m_tee = gst_element_factory_make("tee", "videotee");
    g_assert(m_tee);

    // Display queue
    m_displayQueue = gst_element_factory_make("queue", "displayQueue");
    g_assert(m_displayQueue);    

    m_upload = gst_element_factory_make("glupload", NULL);
    g_assert(m_upload);    

    m_sink = gst_element_factory_make("qmlglsink", NULL);
    g_assert(m_sink);

    // Record queue
    m_recordQueue = gst_element_factory_make("queue", "recordQueue");
    g_assert(m_recordQueue);

    m_encode = gst_element_factory_make("jpegenc", NULL);
    g_assert(m_encode);

    m_mux = gst_element_factory_make("avimux", NULL);
    g_assert(m_mux);

    m_filesink = gst_element_factory_make("filesink", NULL);
    g_assert(m_filesink);

    g_object_set(G_OBJECT(m_filesink), "location", "output.avi", NULL);    

    gst_bin_add_many(GST_BIN (m_pipeline), m_src, m_filter, m_convert, m_crop, m_upload, m_sink, NULL);
    gst_bin_add_many(GST_BIN(m_pipeline), m_tee, m_displayQueue, m_recordQueue, m_encode, m_mux, m_filesink, NULL);

    // If I only link this simple pipeline, it works fine
    /*
   if(!gst_element_link_many(m_src, m_filter, m_convert, m_crop, m_upload, m_sink, NULL)){
        qDebug() << "Unable to link source";
    }
    */

    if(!gst_element_link_many(m_src, m_filter, m_convert, m_crop, m_tee, NULL)){
        qDebug() << "Unable to link source";
    }
    if(!gst_element_link_many(m_displayQueue, m_upload, m_sink, NULL)){
        qDebug() << "Unable to link display queue";
    }
    if(!gst_element_link_many(m_recordQueue, m_encode, m_mux, m_filesink, NULL)){
        qDebug() << "Unable to link record queue";
    }    

    GstPad *teeDisplayPad = gst_element_get_request_pad(m_tee, "src_%u");
    GstPad *queueDisplayPad = gst_element_get_static_pad(m_displayQueue, "sink");

    GstPad *teeRecordPad = gst_element_get_request_pad(m_tee, "src_%u");
    GstPad *queueRecordPad = gst_element_get_static_pad(m_recordQueue, "sink");

    if(gst_pad_link(teeDisplayPad, queueDisplayPad) != GST_PAD_LINK_OK){
        qDebug() << "Unable to link display tee";
    }

    if(gst_pad_link(teeRecordPad, queueRecordPad) != GST_PAD_LINK_OK){
        qDebug() << "Unable to link record tee";
    }

    //gst_object_unref(teeDisplayPad);
    gst_object_unref(queueDisplayPad);
    //gst_object_unref(teeRecordPad);
    gst_object_unref(queueRecordPad);    

    QQuickItem *videoItem = window()->findChild<QQuickItem *> (m_videoItem);
    g_object_set(m_sink, "widget", videoItem, NULL);

    // This will call gst_element_set_state(m_pipeline, GST_STATE_PLAYING) when the window is ready
    window()->scheduleRenderJob (new SetPlaying (m_pipeline), QQuickWindow::BeforeSynchronizingStage);    

    m_bus = gst_element_get_bus(m_pipeline);

    gst_bus_add_watch(m_bus, busCallback, m_loop);
    gst_object_unref(m_bus);

    m_loop = g_main_loop_new(NULL, false);
    g_main_loop_run(m_loop);     
}

static gboolean busCallback(GstBus *bus, GstMessage *message, gpointer data){
    qDebug() << "Callback function reached";
    switch(GST_MESSAGE_TYPE(message)){
        case GST_MESSAGE_ERROR:
            GError *error;
            gchar *debugInfo;
            gst_message_parse_error(message, &error, &debugInfo);
            qDebug() << "Error received from element" << GST_OBJECT_NAME(message->src) << ":" << error->message;
            qDebug() << "Debugging information:" << (debugInfo ? debugInfo : "none");
            //g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (m_message->src), error->message);
            //g_printerr ("Debugging information: %s\n", debugInfo ? debugInfo : "none");
            g_clear_error (&error);
            g_free (debugInfo);

            g_main_loop_quit(static_cast<GMainLoop *>(data));
            break;
        case GST_MESSAGE_EOS:
            qDebug() << "End-Of-Stream reached.";
            g_main_loop_quit(static_cast<GMainLoop *>(data)); 
            break;
        default:
            qDebug() << "Unexpected message received."; 
            break;
        }
    return true;    
}

/**
The rest of the code is probably not relevant. It contains 
only destructor and some getters and setters.
**/

GStreamer::~GStreamer()
{
    gst_object_unref(m_bus);
    gst_element_set_state(m_pipeline, GST_STATE_NULL);
    gst_object_unref(m_pipeline);
}

QString GStreamer::source() const
{
    return m_source;
}

void GStreamer::setSource(const QString &source)
{
    if(source != m_source){
        m_source = source;
    }
}

QString GStreamer::videoItem() const
{
    return m_videoItem;
}

void GStreamer::setVideoItem(const QString &videoItem)
{
    if(videoItem != m_videoItem){
        m_videoItem = videoItem;
    }
}

.h文件中定义了所有成员变量。

如果我不将 tee 元素添加到容器中并将其链接到管道中，则视频会按预期显示在屏幕上。所以我想我弄乱了 T 形元件上的衬垫。

我一直在关注 GStreamers 文档中的教程，所以我不明白为什么它不起作用。

希望有人能提供帮助。

Answer 1

好的，所以提供的 gst-launch 行和应用程序代码之间的区别是使用 qmlglsink 元素代替 glimagesink。

问题是 qmlglsink 只接受 RGBA 格式的视频缓冲区，但是 tee 的另一个分支中的 jpegenc 不接受 RGBA 格式的视频缓冲区。这会导致协商问题，因为 tee.

的两个分支都不支持通用格式

解决方法是在 jpegenc 之前添加一个 videoconvert 元素或在 qmlglsink 之前添加一个 glcolorconvert 元素，以便 tee 的两个分支都可以协商到相同的视频格式。

旁注：glimagesink 内部包含一个 glupload ! glcolorconvert ! actual-sink，因此已经在转换视频格式。

如何在 C 代码中实现 GStreamer tee

How to implement GStreamer tee in C code

gstreamer