MDataSource Class Reference

Destructor.

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.

Deprecated

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

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

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

Deprecated

Returns a buffer created by the data source

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

Deprecated

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.

Returns the UID identifying the type of data source.

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.

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.

Instantiates a data source.

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.

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.

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.

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

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

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'

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.

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.

Indicates whether the data source supports sample rate conversion.

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

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'.

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.

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.