MDataSource Class Reference

class MDataSource

Abstract class representing a data source.

Constructor & Destructor Documentation

MDataSource(TUid)

MDataSource(TUidaType)[protected, inline]

Protected constructor.

Parameters

TUid aType

~MDataSource()

~MDataSource()[inline, virtual]

Destructor.

Member Functions Documentation

BufferEmptiedL(CMMFBuffer *)

voidBufferEmptiedL(CMMFBuffer *aBuffer)[pure virtual]

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

CanCreateSourceBuffer()

TBool CanCreateSourceBuffer()[pure virtual]

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

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

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

ConstructSourceL(const TDesC8 &)

voidConstructSourceL(const TDesC8 &aInitData)[protected, pure virtual]

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 & aInitDataThe source specific initialisation data required for source construction.

CreateSourceBufferL(TMediaId, TBool &)

CMMFBuffer *CreateSourceBufferL(TMediaIdaMediaId,
TBool &aReference
)[pure virtual]

Returns a buffer created by the data source

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

A pointer to the created buffer.

Parameters

TMediaId aMediaIdThis 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 & aReferenceThis 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.

CreateSourceBufferL(TMediaId, CMMFBuffer &, TBool &)

CMMFBuffer *CreateSourceBufferL(TMediaIdaMediaId,
CMMFBuffer &aSinkBuffer,
TBool &aReference
)[inline, virtual]

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.

A pointer to the created buffer.

Parameters

TMediaId aMediaIdThis 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 & aSinkBufferThe sink buffer the nature of which may influence the creation of the source buffer.
TBool & aReferenceThis 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.

DataSourceType()

TUid DataSourceType()const [inline, virtual]

Returns the UID identifying the type of data source.

The UID identifying the type of data source.

FillBufferL(CMMFBuffer *, MDataSink *, TMediaId)

voidFillBufferL(CMMFBuffer *aBuffer,
MDataSink *aConsumer,
TMediaIdaMediaId
)[pure virtual]

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 * aBufferThe buffer that needs filling with data.
MDataSink * aConsumerThe 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 aMediaIdThis 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.

NegotiateSourceL(MDataSink &)

voidNegotiateSourceL(MDataSink &aDataSink)[inline, virtual]

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 & aDataSinkThe data sink whose settings can affect the data source.

NewSourceL(TUid, const TDesC8 &)

MDataSource *NewSourceL(TUidaImplementationUid,
const TDesC8 &aInitData
)[static, inline]

Instantiates a data source.

The instantiated data source.

Parameters

TUid aImplementationUidThe UID identifying the data source to be instantiated.
const TDesC8 & aInitDataThe source specific initialisation data required for source construction.

SetSourceDataTypeCode(TFourCC, TMediaId)

TInt SetSourceDataTypeCode(TFourCCaSourceFourCC,
TMediaIdaMediaId
)[inline, virtual]

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.

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

Parameters

TFourCC aSourceFourCCThis specifies the data type as a fourCC code to set the source to.
TMediaId aMediaIdThis 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.

SetSourcePrioritySettings(const TMMFPrioritySettings &)

voidSetSourcePrioritySettings(const TMMFPrioritySettings &aPrioritySettings)[inline, virtual]

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 & aPrioritySettingsThe source priority settings.

SourceCustomCommand(TMMFMessage &)

voidSourceCustomCommand(TMMFMessage &aMessage)[inline, virtual]

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 & aMessageThe message specifying the custom command.

SourceDataTypeCode(TMediaId)

TFourCC SourceDataTypeCode(TMediaIdaMediaId)[pure virtual]

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

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

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

Parameters

TMediaId aMediaIdThis 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.

SourcePauseL()

voidSourcePauseL()[inline, virtual]

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'

SourcePlayL()

voidSourcePlayL()[inline, virtual]

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.

SourcePrimeL()

voidSourcePrimeL()[inline, virtual]

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.

SourceSampleConvert()

TBool SourceSampleConvert()[inline, virtual]

Indicates whether the data source supports sample rate conversion.

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

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

SourceStopL()

voidSourceStopL()[inline, virtual]

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'.

SourceThreadLogoff()

voidSourceThreadLogoff()[inline, virtual]

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.

SourceThreadLogon(MAsyncEventHandler &)

TInt SourceThreadLogon(MAsyncEventHandler &aEventHandler)[inline, virtual]

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.

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

Parameters

MAsyncEventHandler & aEventHandlerThis 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.

Member Data Documentation

TUid iDataSourceType

TUid iDataSourceType[private]

TUid iDtor_ID_Key

TUid iDtor_ID_Key[private]