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applicationsource.h

/*
    Copyright (C) 2011 Collabora Ltd. <info@collabora.co.uk>
      @author George Kiagiadakis <george.kiagiadakis@collabora.co.uk>

    This library is free software; you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation; either version 2.1 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef QGST_UTILS_APPLICATIONSOURCE_H
#define QGST_UTILS_APPLICATIONSOURCE_H

#include "global.h"
#include "../element.h"
#include "../buffer.h"

namespace QGst {
namespace Utils {

/*! \headerfile applicationsource.h <QGst/Utils/ApplicationSource>
 * \brief Helper class for using a GstAppSrc
 *
 * Appsrc is an element that can be used by applications to insert data into a GStreamer
 * pipeline. Unlike most GStreamer elements, appsrc provides external API functions.
 * This class exports those API functions in the bindings and makes it easy to implement
 * a custom source.
 *
 * Before operating appsrc, the caps() must be set to a fixed caps describing the format
 * of the data that will be pushed with appsrc. An exception to this is when pushing buffers
 * with unknown caps, in which case no caps should be set. This is typically true of file-like
 * sources that push raw byte buffers.
 *
 * The main way of handing data to the appsrc element is by calling the pushBuffer() method.
 * This will put the buffer onto a queue from which appsrc will read from in its streaming thread.
 * It is important to note that data transport will not happen from the thread that performed
 * the pushBuffer() call.
 *
 * maxBytes() controls how much data can be queued in appsrc before appsrc considers the queue full.
 * A filled internal queue will always cause enoughData() to be called, which signals the
 * application that it should stop pushing data into appsrc. Use setBlock() to cause appsrc to
 * block the pushBuffer() method until free data becomes available again.
 *
 * When the internal queue is running out of data, the needData() function is called, which signals
 * the application that it should start pushing more data into appsrc.
 *
 * In addition to the needData() and enoughData() functions, appsrc can also call the seekData()
 * function when streamMode() is set to AppStreamTypeSeekable or AppStreamTypeRandomAccess.
 * The  seekData() argument will contain the new desired position in the stream expressed in the
 * unit set with setFormat(). After seekData() has been called, the application should push buffers
 * from the new position.
 *
 * Appsrc can operate in two different ways:
 *
 * \li The push model, in which the application repeadedly calls the pushBuffer() method with
 * a new buffer. Optionally, the queue size in the appsrc can be controlled with the enoughData()
 * and needData() functions by respectively stopping/starting the pushBuffer() calls. This is a
 * typical mode of operation for the stream types AppStreamTypeStream and AppStreamTypeSeekable.
 * Use this model when implementing various network protocols or hardware devices.
 *
 * \li The pull model where the needData() function triggers the next pushBuffer() call. This mode
 * is typically used in the AppStreamTypeRandomAccess stream type. Use this model for file access
 * or other randomly accessable sources. In this mode, a buffer of exactly the amount of bytes
 * given by the needData() function should be pushed into appsrc.
 *
 * In all modes, the size() should contain the total stream size in bytes. Setting the size is
 * mandatory in the AppStreamTypeRandomAccess mode. For the AppStreamTypeStream and
 * AppStreamTypeSeekable modes, setting the size is optional but recommended.
 *
 * When the application is finished pushing data into appsrc, it should call endOfStream().
 * After this call, no more buffers can be pushed into appsrc until a flushing seek happened or
 * the state of the appsrc has gone through READY.
 *
 * The actuall appsrc element can be retrieved with element() and set with setElement(). It is
 * not necessary to set an appsrc, as this class will create one as soon as it is needed.
 *
 * \note It is not necessary to use this class in order to use GstAppSrc. GstAppSrc
 * also provides signals and properties that fully substitute the functionality of this class.
 *
 * \sa ApplicationSink
 */
class QTGSTREAMERUTILS_EXPORT ApplicationSource
{
public:
    ApplicationSource();
    virtual ~ApplicationSource();

    /*! \returns the appsrc element */
    ElementPtr element() const;

    /*! Sets the appsrc element that will be used by this class */
    void setElement(const ElementPtr & appsrc);


    /*! \returns the caps that the appsrc is configured to produce */
    CapsPtr caps() const;

    /*! Sets the capabilities of this source. After calling this method,
     * this appsrc will only be able to produce buffers with these capabilities.
     * \a caps must be fixed and the caps on the buffers must match the \a caps or left NULL.
     */
    void setCaps(const CapsPtr & caps);


    /*! \returns the minimum latency of this element */
    quint64 minLatency() const;

    /*! \returns the maximum latency of this element */
    quint64 maxLatency() const;

    /*! Configure the minimum and maximum latency. If \a min is set to -1,
     * the default latency calculations for pseudo-live sources will be used. */
    void setLatency(quint64 min, quint64 max);


    /*! \returns the size of the stream in bytes.
     * A value of -1 means that the size is not known. */
    qint64 size() const;

    /*! Set the size of the stream in bytes.
     * A value of -1 means that the size is not known. */
    void setSize(qint64 size);


    /*! \returns the stream type of this appsrc */
    AppStreamType streamType() const;

    /*! Set the stream type on appsrc. For seekable streams,
     * the seekData() method must be reimplemented. */
    void setStreamType(AppStreamType type);


    /*! \returns the maximum amount of bytes that can be queued in appsrc */
    quint64 maxBytes() const;

    /*! Set the maximum amount of bytes that can be queued in appsrc. After
     * the maximum amount of bytes are queued, the enoughData() method of
     * this class will be called. */
    void setMaxBytes(quint64 max);


    /*! \returns true if appsrc is configured to block any calls
     * to pushBuffer() when the maximum amount of bytes are queued. */
    bool blockEnabled() const;

    /*! Enables or disables blocking calls to pushBuffer()
     * when the maximum amount of bytes are queued. */
    void enableBlock(bool enable);


    /*! \returns true if the appsrc is configured to act as a live source */
    bool isLive() const;

    /*! Sets whether appsrc will act as a live source */
    void setLive(bool islive);


    /*! \returns the minimum percent of maxBytes() that
     * when reached, needData() will be called */
    uint minPercent() const;

    /*! Sets the minimum percent of maxBytes() that
     * when reached, needData() will be called */
    void setMinPercent(uint min);


    Format format() const;
    void setFormat(Format f);


    /*! Adds a buffer to the queue of buffers that the appsrc element will
     * push to its source pad. When the block property is TRUE, this function
     * can block until free space becomes available in the queue.
     *
     * \returns FlowOk when the buffer was successfuly queued, FlowWrongState when
     * appsrc is not PAUSED or PLAYING or FlowUnexpected when EOS occured.
     */
    FlowReturn pushBuffer(const BufferPtr & buffer);

    /*! Indicates to the appsrc element that the last buffer queued
     * in the element is the last buffer of the stream.
     *
     * \returns FlowOk when the EOS was successfuly queued or
     * FlowWrongState when appsrc is not PAUSED or PLAYING.
     */
    FlowReturn endOfStream();

protected:
    /*! Called when the appsrc needs more data. A buffer or EOS should be pushed
     * to appsrc from this thread or another thread. length is just a hint and when
     * it is set to -1, any number of bytes can be pushed into appsrc. */
    virtual void needData(uint length);

    /*! Called when appsrc has enough data. It is recommended that the application
     * stops calling pushBuffer() until the needData() method is called again to
     * avoid excessive buffer queueing. */
    virtual void enoughData();

    /*! Called when a seek should be performed to the offset. The next pushBuffer()
     * should produce buffers from the new offset. This method is only called for
     * seekable stream types. */
    virtual bool seekData(quint64 offset);

private:
    /* vtable padding */
    virtual void reservedVirtual1() {}
    virtual void reservedVirtual2() {}
    virtual void reservedVirtual3() {}
    virtual void reservedVirtual4() {}

private:
    struct Priv;
    friend struct Priv;
    Priv *const d;
    Q_DISABLE_COPY(ApplicationSource)
};

} //namespace Utils
} //namespace QGst

#endif // QGST_UTILS_APPLICATIONSOURCE_H

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