2

我开发了一个基于 Qt 和 QtGstreamer 的视频播放器。它用于播放实时流 (RTSP)。我必须增加用户在播放实时流时拍摄快照而不干扰视频播放的可能性。

这是我制作的管道图：

                                -->queue-->autovideosink
uridecodebin-->videoflip-->tee--|
            |                   -->queue->videoconvert-->pngenc-->filesink
            |
            |->audioconvert-->autoaudiosink

我使用pad-added来自的信号uridecodebin将我的元素动态添加和链接到管道，接收到的上限的功能。

void Player::onPadAdded(const QGst::PadPtr &pad)
{
    QGst::CapsPtr caps = pad->currentCaps();
    if (caps->toString().startsWith("video/x-raw")) {
        qDebug("Received 'video/x-raw' caps");
        handleNewVideoPad(pad);
    }
    else if (caps->toString().startsWith("audio/x-raw")) {
        qDebug("Received 'audio/x-raw' caps");
        if (!m_audioEnabled) {
            qDebug("Audio is disabled in the player. Ignoring...");
            return;
        }
        handleNewAudioPad(pad);
    }
    else {
        qWarning("Unsuported caps, arborting ...!");
        return;
    }
}

[...]

void Player::handleNewVideoPad(QGst::PadPtr pad)
{
    m_player->videoTeeVideoSrcPad = m_player->videoTee->getRequestPad("src_%u");

    // Add video elements
    m_player->pipeline->add(m_player->videoFlip);
    m_player->pipeline->add(m_player->videoTee);
    m_player->pipeline->add(m_player->videoQueue);
    m_player->pipeline->add(m_player->videoSink);

    // Add snap elements
    m_player->pipeline->add(m_player->snapQueue);
    m_player->pipeline->add(m_player->snapConverter);
    m_player->pipeline->add(m_player->snapEncoder);
    m_player->pipeline->add(m_player->snapSink);

    // Link video elements
    m_player->videoFlip->link(m_player->videoTee);
    m_player->videoQueue->link(m_player->videoSink);

    // Link snap elements
    m_player->snapQueue->link(m_player->snapConverter);
    m_player->snapConverter->link(m_player->snapEncoder);
    m_player->snapEncoder->link(m_player->snapSink);

    // Lock snap elements
    m_player->snapQueue->setStateLocked(true);
    m_player->snapConverter->setStateLocked(true);
    m_player->snapEncoder->setStateLocked(true);
    m_player->snapSink->setStateLocked(true);

    m_player->videoFlip->setState(QGst::StatePlaying);
    m_player->videoTee->setState(QGst::StatePlaying);
    m_player->videoQueue->setState(QGst::StatePlaying);
    m_player->videoSink->setState(QGst::StatePlaying);

    // Link pads
    m_player->videoTeeVideoSrcPad->link(m_player->videoQueue->getStaticPad("sink"));
    pad->link(m_player->videoSinkPad);

    m_player->videoLinked = true;
}

拍摄快照的方法：

void Player::takeSnapshot()
{
    QDateTime dateTime = QDateTime::currentDateTime();
    QString snapLocation = QString("/%1/snap_%2.png").arg(m_snapDir).arg(dateTime.toString(Qt::ISODate));

    m_player->inSnapshotCaputre = true;

    if (m_player->videoTeeSnapSrcPad) {
        m_player->videoTee->releaseRequestPad(m_player->videoTeeSnapSrcPad);
        m_player->videoTeeSnapSrcPad.clear();
    }
    m_player->videoTeeSnapSrcPad = m_player->videoTee->getRequestPad("src_%u");

    // Stop the snapshot branch
    m_player->snapQueue->setState(QGst::StateNull);
    m_player->snapConverter->setState(QGst::StateNull);
    m_player->snapEncoder->setState(QGst::StateNull);
    m_player->snapSink->setState(QGst::StateNull);

    // Link Tee src pad to snap queue sink pad
    m_player->videoTeeSnapSrcPad->link(m_player->snapQueue->getStaticPad("sink"));

    // Set the snapshot location property
    m_player->snapSink->setProperty("location", snapLocation);

    // Unlock snapshot branch
    m_player->snapQueue->setStateLocked(false);
    m_player->snapConverter->setStateLocked(false);
    m_player->snapEncoder->setStateLocked(false);
    m_player->snapSink->setStateLocked(false);
    m_player->videoTeeSnapSrcPad->setActive(true);

    // Synch snapshot branch state with parent
    m_player->snapQueue->syncStateWithParent();
    m_player->snapConverter->syncStateWithParent();
    m_player->snapEncoder->syncStateWithParent();
    m_player->snapSink->syncStateWithParent();
}

总线消息回调：

void Player::onBusMessage(const QGst::MessagePtr & message)
{
    QGst::ElementPtr source = message->source().staticCast<QGst::Element>();
    switch (message->type()) {
    case QGst::MessageEos: { //End of stream. We reached the end of the file.
        qDebug("Message End Off Stream");
        if (m_player->inSnapshotCaputre) {
            blockSignals(true);
            pause();
            play();
            blockSignals(false);
            m_player->inSnapshotCaputre = false;
        }
        else {
            m_eos = true;
            stop();
        }
        break;
    }
    [...]
}

问题是：

  • 当我将元素的属性设置为时，我收到停止管道的snapshot事件，所以我需要重新启动它，这会冻结视频播放大约半秒，这在我的情况下是不可接受的。truepngencEOS
  • 当我将元素的属性snapshot设置为时，我没有管道扰动，但我的 png 文件不断增长，直到我再次调用该方法。falsepngencPlayer::takeSnapshot()

我哪里错了？有更好的方法吗？我尝试为我的分支创建一个QGst::Bin元素，但没有成功。snapshot焊盘探针呢？

提前致谢

4

2 回答 2

3

您可以在任何接收器上获取 last-sample 属性，例如您的视频接收器。这包含一个 GstSample，它有一个缓冲区，其中包含最新的视频帧。您可以将其作为快照，例如使用 gst_video_convert_sample() 或其异步变体，将其转换为 PNG/JPG/其他格式。

请参阅https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer-libs/html/GstBaseSink.html#GstBaseSink--last-sample和https://gstreamer.freedesktop.org/data/doc/ gstreamer/head/gst-plugins-base-libs/html/gst-plugins-base-libs-gstvideo.html#gst-video-convert-sample

或者，您必须在第一帧之后关闭文件接收器快照管道。例如，通过填充探针了解第一帧何时发生，然后注入 EOS 事件以防止将更多 PNG 帧附加到同一文件中。

于 2016-03-16T09:56:56.317 回答
3

感谢@sebastian-droge 的回答，我找到了解决方案，使用我的视频接收器gst_video_convert_sample的last-sample属性。

我实施的解决方案是：

void Player::takeSnapshot()
{
    QDateTime currentDate = QDateTime::currentDateTime();
    QString location = QString("%1/snap_%2.png").arg(QDir::homePath()).arg(currentDate.toString(Qt::ISODate));
    QImage snapShot;
    QImage::Format snapFormat;
    QGlib::Value val = m_videoSink->property("last-sample");
    GstSample *videoSample = (GstSample *)g_value_get_boxed(val);
    QGst::SamplePtr sample = QGst::SamplePtr::wrap(videoSample);
    QGst::SamplePtr convertedSample;
    QGst::BufferPtr buffer;
    QGst::CapsPtr caps = sample->caps();
    QGst::MapInfo mapInfo;
    GError *err = NULL;
    GstCaps * capsTo = NULL;
    const QGst::StructurePtr structure = caps->internalStructure(0);
    int width, height;

    width = structure.data()->value("width").get<int>();
    height = structure.data()->value("height").get<int>();

    qDebug() << "Sample caps:" << structure.data()->toString();

    /*
     * { QImage::Format_RGBX8888, GST_VIDEO_FORMAT_RGBx  },
     * { QImage::Format_RGBA8888, GST_VIDEO_FORMAT_RGBA  },
     * { QImage::Format_RGB888  , GST_VIDEO_FORMAT_RGB   },
     * { QImage::Format_RGB16   , GST_VIDEO_FORMAT_RGB16 }
     */
    snapFormat = QImage::Format_RGB888;
    capsTo = gst_caps_new_simple("video/x-raw",
                                 "format", G_TYPE_STRING, "RGB",
                                 "width", G_TYPE_INT, width,
                                 "height", G_TYPE_INT, height,
                                 NULL);

    convertedSample = QGst::SamplePtr::wrap(gst_video_convert_sample(videoSample, capsTo, GST_SECOND, &err));
    if (convertedSample.isNull()) {
        qWarning() << "gst_video_convert_sample Failed:" << err->message;
    }
    else {
        qDebug() << "Converted sample caps:" << convertedSample->caps()->toString();

        buffer = convertedSample->buffer();
        buffer->map(mapInfo, QGst::MapRead);

        snapShot = QImage((const uchar *)mapInfo.data(),
                          width,
                          height,
                          snapFormat);

        qDebug() << "Saving snap to" << location;
        snapShot.save(location);

        buffer->unmap(mapInfo);
    }

    val.clear();
    sample.clear();
    convertedSample.clear();
    buffer.clear();
    caps.clear();
    g_clear_error(&err);
    if (capsTo)
        gst_caps_unref(capsTo);
}

我创建了一个简单的测试应用程序，它实现了这个解决方案。代码在我的Github上可用

于 2016-03-19T16:56:51.683 回答