Class MDataSource

class MDataSource;

Description

Abstract class representing a data source.

Members

Defined in MDataSource:
BufferEmptiedL(), CanCreateSourceBuffer(), ConstructSourceL(), CreateSourceBufferL(), CreateSourceBufferL(), DataSourceType(), FillBufferL(), MDataSource(), NegotiateSourceL(), NewSourceL(), SetSourceDataTypeCode(), SetSourcePrioritySettings(), SourceCustomCommand(), SourceDataTypeCode(), SourcePauseL(), SourcePlayL(), SourcePrimeL(), SourceSampleConvert(), SourceStopL(), SourceThreadLogoff(), SourceThreadLogon(), ~MDataSource()

inline virtual ~MDataSource();

Description

Destructor.

protected: inline MDataSource(TUid aType);

Description

Protected constructor.

Parameters

TUid aType

static inline MDataSource *NewSourceL(TUid aImplementationUid, const TDesC8 &aInitData);

Description

Instantiates a data source.

Parameters

TUid aImplementationUid The UID identifying the data source to be instantiated. const TDesC8 &aInitData The source specific initialisation data required for source construction.

Return value

MDataSource * The instantiated data source.

inline virtual TUid DataSourceType() const;

Description

Returns the UID identifying the type of data source.

Return value

TUid The UID identifying the type of data source.

virtual TFourCC SourceDataTypeCode(TMediaId aMediaId)=0;

Description

Returns the data type as a fourCC code of the data source.

This is a pure virtual function that each derrived class must implement.

Parameters

TMediaId aMediaId This identifies the type of media eg. audio or video and the stream ID. This parameter is required in cases where the source can supply data of more than one media type and/or multiple streams of data.

Return value

TFourCC The fourCC code identifying the source datatype for the specified aMediaId.

inline virtual TInt SetSourceDataTypeCode(TFourCC aSourceFourCC, TMediaId aMediaId);

Description

Sets the data type as a fourCC code for the data source.

This is a virtual function that each derived class can implement if the data source supports the ability to have its data type set.

Parameters

TFourCC aSourceFourCC This specifies the data type as a fourCC code to set the source to. TMediaId aMediaId This identifies the type of media eg. audio or video and the stream ID. This parameter is required in cases where the source can supply data of more than one media type and/or multiple strams of data eg a multimedia file.

Return value

TInt KErrNone if successful, KErrNotSupported if the source does not support having it's data type set, otherwise a system wide error code.

virtual void FillBufferL(CMMFBuffer *aBuffer, MDataSink *aConsumer, TMediaId aMediaId)=0;

Description

Function called by a MDataSink to request the data source to fill aBuffer with data.

This is a pure virtual function that each derived class must implement. This method is used when a data source is passively waiting for requests from a consumer ie. a data sink to fill a buffer. The data source must call the BufferFilledL member on aConsumer when it has filled the buffer with data. The data source can either make this callback synchronously or asynchronously.

The format should read the frame number of the buffer via the buffer's CMMFBuffer::FrameNumber() function. From this, the format should be able to determine the actual position of the data on the data source. The technique here depends on the nature of the format. For a linear audio format, the position can be obtained by a simple calculation of the frame size, the header size and where appropriate the datatype.

For non-linear formats, either an index table of frame number and location will need to be created in the NewL() or some form of approximating algorithm will be required. Some formats have an index table as part of the format eg. AVI. If no random access is required then no index table is required, the format can keep track of the current read position and increment it on each access, and reset it if the frame number is reset to 0 or 1. Given that for non-linear ie. variable bit rate formats, the size of the data read may vary from frame to frame, then the format should either set the request size of the buffer for the required frame or call the source's ReadBufferL() (either CMMFClip::ReadBufferL(), CMMFDescriptor ::ReadBufferL() or CMMFFile::ReadBufferL()) function that takes the aLength parameter.

It is the responsibility of the format decode to determine the size and position of the source data for each frame. For linear audio formats, the format decode should fill the buffer up to its maximum length. For multimedia formats e.g. mp4, AVI etc, the format decode is effectively acting as a demultiplexor, and must obtain the appropriate data from the source depending on the aMediaId.

Parameters

CMMFBuffer *aBuffer The buffer that needs filling with data. MDataSink *aConsumer The data sink that consumes the data. The data source needs this to make the BufferFilledL callback on aConsumer when the data source has completed filling the aBuffer. TMediaId aMediaId This identifies the type of media eg. audio or video and the stream ID. This parameter is required in cases where the source can supply data of more than one media type and/or multiple strams of data eg. a multimedia file.

virtual void BufferEmptiedL(CMMFBuffer *aBuffer)=0;

Description

Function called by a data sink to pass back an emptied buffer to the source.

This is a pure virtual function that each derived class must implement. This method is used as the callback when the data source actively requests a consumer ie. a data sink to empty a buffer by calling the data sinks EmptyBufferL. When the data source gets this callback it knows that the buffer has been emptied and can be reused.

Parameters

CMMFBuffer *aBuffer The buffer that has been emptied by a data sink and is now available for reuse.

virtual TBool CanCreateSourceBuffer()=0;

Description

Function to indicate whether the data source can create a buffer.

This is a pure virtual function that each derived class must implement.

Return value

TBool A boolean indicating if the data source can create a buffer. ETrue if it can otherwise EFalse.

virtual CMMFBuffer *CreateSourceBufferL(TMediaId aMediaId, TBool &aReference)=0;

Description

Returns a buffer created by the data source

This is a pure virtual function that each derived class must implement.

Parameters

TMediaId aMediaId This identifies the type of media eg. audio or video and the stream ID. This parameter is required in cases where the source can supply data of more than one media type and/or multiple strams of data eg a multimedia file. TBool &aReference This must be written to by the method to indicate whether the created buffer is a 'reference' buffer. A 'reference' buffer is a buffer that is owned by the source and should be used in preference to the sink buffer provided the sink buffer is also not a reference buffer.

Return value

CMMFBuffer * A pointer to the created buffer.

inline virtual CMMFBuffer *CreateSourceBufferL(TMediaId aMediaId, CMMFBuffer &aSinkBuffer, TBool &aReference);

Description

Returns a buffer created by the data source.

This is a virtual function that a derived class can implement. This can be used in preference to the above CreateSourceBufferL method in cases where the source buffer creation has a dependancy on the sink buffer.

Parameters

TMediaId aMediaId This identifies the type of media eg. audio or video and the stream ID. This parameter is required in cases where the source can supply data of more than one media type and/or multiple strams of data eg a multimedia file CMMFBuffer &aSinkBuffer The sink buffer the nature of which may influence the creation of the source buffer. TBool &aReference This must be written to by the method to indicate whether the created buffer is a 'reference' buffer. A 'reference' buffer is a buffer that is owned by the source and should be used in preference to the sink buffer provided the sink buffer is not a reference buffer.

Return value

CMMFBuffer * A pointer to the created buffer.

inline virtual TInt SourceThreadLogon(MAsyncEventHandler &aEventHandler);

Description

Function to 'logon' the data source to the same thread that source will be supplying data in.

This method may be required as the thread that the data source was created in is not always the same thread that the data transfer will take place in. Therefore any thread specific initialisation needs to be performed in the SourceThreadLogon rather than in the creation of the data source.

This is a virtual function that a derrived data source can implement if any thread specific initialisation is required and/or the data source can create any asynchronous events.

Parameters

MAsyncEventHandler &aEventHandler This is an MAsyncEventHandler to handle asynchronous events that occur during the transfer of multimedia data. The event handler must be in the same thread as the data transfer thread. Hence the reason it is passed in the SourceThreadLogon as opposed to say the constructor.

Return value

TInt An error code indicating if the function call was successful. KErrNone on success, otherwise another of the system-wide error codes.

inline virtual void SourceThreadLogoff();

Description

Function to 'logoff' the data source from the same thread that source supplies data in.

This method may be required as the thread that the data source is deleted in may not be the same thread that the data transfer took place in. Therefore any thread specific releasing of resources needs to be performed in the SourceThreadLogoff rather than in the destructor.

This is a virtual function that a derrived data source can implement if any thread specific releasing of resources is required.

inline virtual void NegotiateSourceL(MDataSink &aDataSink);

Description

Function to allow the data source to negotiate with a data sink

This method is required in cases where the settings of data source are dependant on those of a data sink. This is a virtual function that a derrived data source can implement.

Parameters

MDataSink &aDataSink The data sink whose settings can affect the data source.

inline virtual TBool SourceSampleConvert();

Description

Indicates whether the data source supports sample rate conversion.

This is a virtual function that a derived class can implement.

Return value

TBool A boolean indicating if the data source can perform a sample rate conversion. ETrue if it can otherwise EFalse.

inline virtual void SourcePrimeL();

Description

Function to 'prime' the data source.

This is a virtual function that a derrived data source can implement if any data source specific 'priming' is required.

inline virtual void SourcePlayL();

Description

Function to 'play' the data source.

This is a virtual function that a derrived data source can implement if any data source specific action is required prior to 'playing' ie. the start of data transfer.

inline virtual void SourcePauseL();

Description

Function to 'pause' the data source.

This is a virtual function that a derrived data source can implement if any data source specific action is required to 'pause'

inline virtual void SourceStopL();

Description

Function to 'stop' the data source.

This is a virtual function that a derrived data source can implement if any data source specific action is required to 'stop'.

Capability:

MultimediaDD

A process requesting or using this method that has MultimediaDD capability will always have precedence over a process that does not have MultimediaDD.

inline virtual void SetSourcePrioritySettings(const TMMFPrioritySettings &aPrioritySettings);

Description

Function to set the source priority settings.

This is a virtual function that a derrived data source can implement if a priority mechanism is required to arbitrate between multiple clients trying to access the same resource.

Parameters

const TMMFPrioritySettings &aPrioritySettings The source priority settings.

inline virtual void SourceCustomCommand(TMMFMessage &aMessage);

Description

Function to call a source specific custom command.

This is a virtual function that a derrived data source can implement if it implements any custom commands.

Parameters

TMMFMessage &aMessage The message specifying the custom command.

protected: virtual void ConstructSourceL(const TDesC8 &aInitData)=0;

Description

Performs any source construction dependant on the source construction initialisation data aInitData.

This is a pure virtual function that a derrived data source must implement

Parameters

const TDesC8 &aInitData The source specific initialisation data required for source construction.