Tutorial: Simple Media Engine

Files:

• ffmpeg/ffmpegdirectpainterwidget.cpp
• ffmpeg/ffmpegdirectpainterwidget.h
• ffmpeg/ffmpegengine.cpp
• ffmpeg/ffmpegengine.h
• ffmpeg/ffmpegenginefactory.cpp
• ffmpeg/ffmpegenginefactory.h
• ffmpeg/ffmpegengineinformation.cpp
• ffmpeg/ffmpegengineinformation.h
• ffmpeg/ffmpegplaybinsession.cpp
• ffmpeg/ffmpegplaybinsession.h
• ffmpeg/ffmpegsinkwidget.cpp
• ffmpeg/ffmpegsinkwidget.h
• ffmpeg/ffmpegurisessionbuilder.cpp
• ffmpeg/ffmpegurisessionbuilder.h
• ffmpeg/qbuild.pro

The Ffmpeg Media Engine tutorial shows how to use the Qt Extended Media API to create a simple Media Engine.

The engine requires ffmpeg installed into your system or toolchain. This engine is for demonstration purposes only.

Firstly ffmpeg requires initialization, this is added to ffmpegengine.cpp

    av_register_all();

Everything else goes into ffmpegplaybinsession.cpp In constructor open audio output

    d->output = new QAudioOutput(this);

Create video output, wrapper class for QVideoFrame, see ffmpegdirectpainterwidget.cpp

    d->sinkWidget = new DirectPainterWidget;

Ffmpeg's open and codec functions

    av_open_input_file();
    av_find_stream_info();
    avcodec_find_decoder();
    avcodec_open();
    avcodec_alloc_frame();

Once we have all the information about the file to play we can register if it has video to play.

    d->videoControlServer = new QMediaVideoControlServer(d->id);
    d->videoControlServer->setVideoDelegate(d->sinkWidget->videoSurface());
    d->videoControlServer->setRenderTarget(d->sinkWidget->windowId());
    d->interfaces << "Video";
    emit interfaceAvailable("Video");
    d->haveStreamInfo = true;

When the system is ready to start playback void PlaybinSession::start() is called to begin, readFrame() is called to decode and output the audio and video data.

    av_read_frame();
    // audio output
    d->output->write((const char*)audio_buf,(qint64)data_size);
    // video output
    d->sinkWidget->paint(*f);

    class QMediaEngineInformation;
    class QMediaSessionRequest;
    class QMediaServerSession;

    namespace ffmpeg
    {

    class EnginePrivate;

    class Engine : public QMediaEngine
    {
        Q_OBJECT

    public:
        Engine();
        ~Engine();

        void initialize();

        void start();
        void stop();

        void suspend();
        void resume();

        QMediaEngineInformation const* engineInformation();

        void registerSession(QMediaServerSession* session);
        void unregisterSession(QMediaServerSession* session);

    private:
        PlaybinSession*   s;
        EnginePrivate*    d;
    };

    class PlaybinSessionPrivate;

    class PlaybinSession : public QMediaServerSession
    {
        Q_OBJECT

    public:
        PlaybinSession(Engine* engine, QUuid const& id, QUrl const& url,
                QMediaDevice* sink);
        ~PlaybinSession();

        bool isValid() const;

        void start();
        void pause();
        void stop();

        void suspend();
        void resume();

        void seek(quint32 ms);
        quint32 length();

        void setVolume(int volume);
        int volume() const;

        void setMuted(bool mute);
        bool isMuted() const;

        QtopiaMedia::State playerState() const;

        QString errorString();

        void setDomain(QString const& domain);
        QString domain() const;

        QStringList interfaces();

        QString id() const;
        QString reportData() const;

    private slots:
        void readFrame();

    private:
        void getStreamsInfo();
        void readySession();

        PlaybinSessionPrivate*  d;
    };