Symbian
Symbian OS Library

SYMBIAN OS V9.3

[Index] [Spacer] [Previous] [Next]



Location: mmfformat.h
Link against: mmfserverbaseclasses.lib

This item is not part of the S60 3rd Edition SDK for Symbian OS, Feature Pack 2.

Class CMMFFormatDecode

class CMMFFormatDecode : public CBase, public MDataSource, public MDataSink;

Description

Base class from which source formats can be derived from. The intended usage is for controllers that can support more than one type of format. The class is an MDataSource as far as the data path is concerned but is an MDataSink to the clip that is the source of the actual data.

All CMMFFormatDecode plugin DLLs must include interface_uid = KMmfUidPluginInterfaceFormatDecode in their .rss files.

Derivation

Members

Defined in CMMFFormatDecode:
BitRate(), BufferFilledL(), CMMFFormatDecode(), CanCreateSinkBuffer(), CanCreateSourceBuffer(), CreateSinkBufferL(), CreateSourceBufferL(), Duration(), FillBufferL(), FrameTimeInterval(), GetNumberOfMetaDataEntriesL(), GetSupportedBitRatesL(), GetSupportedDataTypesL(), GetSupportedNumChannelsL(), GetSupportedSampleRatesL(), ImplementationUid(), MetaDataEntryL(), NewL(), NewL(), NewL(), NewL(), NewL(), NewL(), NewL(), NumChannels(), PositionL(), SampleRate(), SetBitRate(), SetNumChannels(), SetPositionL(), SetSampleRate(), SinkDataTypeCode(), SourceDataTypeCode(), Streams(), SuggestSourceBufferSize(), iClip, iDataPath, ~CMMFFormatDecode()

Inherited from CBase:
Delete(), Extension_(), operator new()

Inherited from MDataSink:
ConstructSinkL(), DataSinkType(), EmptyBufferL(), NegotiateL(), NewSinkL(), SetSinkDataTypeCode(), SetSinkPrioritySettings(), SinkCustomCommand(), SinkPauseL(), SinkPlayL(), SinkPrimeL(), SinkStopL(), SinkThreadLogoff(), SinkThreadLogon()

Inherited from MDataSource:
BufferEmptiedL(), ConstructSourceL(), DataSourceType(), NegotiateSourceL(), NewSourceL(), SetSourceDataTypeCode(), SetSourcePrioritySettings(), SourceCustomCommand(), SourcePauseL(), SourcePlayL(), SourcePrimeL(), SourceSampleConvert(), SourceStopL(), SourceThreadLogoff(), SourceThreadLogon()


Construction and destruction


NewL()

static IMPORT_C CMMFFormatDecode *NewL(TUid aUid, MDataSource *aSource);

Description

Allocates and constructs an ECom format decode object.

This is used to explicitly instantiate a format decoder where the UID is known. This method might be used by controllers that only support one type of format such that the UID of the format is already known. For example, if an mp3 controller has been instantiated, there is no need for any further format recognition as this has already been performed in the controller instantiation, thus the controller can instantiate an mp3 format directly from it’s UID.

Parameters

TUid aUid

The implementation UID. This is used by Com to create the plugin.

MDataSource *aSource

The controller MDataSource and is the source of the data for the format decode plugin. The format decode plugin is the sink of data for the MDataSource.

Return value

CMMFFormatDecode *

If successful, returns the address of the format decode plugin object created. If not successful, leaves with KErrNotFound.


NewL()

static IMPORT_C CMMFFormatDecode *NewL(const TDesC &aFileName, MDataSource *aSource, const TDesC &aPreferredSupplier);

Description

Parameters

const TDesC &aFileName

MDataSource *aSource

const TDesC &aPreferredSupplier

Return value

CMMFFormatDecode *


NewL()

static IMPORT_C CMMFFormatDecode *NewL(const TDesC8 &aSourceHeader, MDataSource *aSource, const TDesC &aPreferredSupplier);

Description

Attempts to locate and instantiate a CMMFFormatDecode using data in a buffer. The buffer is expected to contain header data (from a file, stream or descriptor).

Signatures (supplied by the plugin registry information) are sought in aSourceHeader.

This function uses the match string as a resolver parameter. The format base class uses the match string to find a match to the match string defined in the opaque_data field of the resource file. The match string would typically be a signature for a particular format usually defined in the format header.

Parameters

const TDesC8 &aSourceHeader

The data which is searched for matching signatures.

MDataSource *aSource

The controller's MDataSource and the source of the data for the format decode plugin.

const TDesC &aPreferredSupplier

If this is provided the list of matching plugins will be further searched for the latest version of a plugin supplied by the specified supplier.

Return value

CMMFFormatDecode *

If successful returns an instantiated CMMFFormatDecode from a plugin. If not successful, leaves with KErrNotFound.


NewL()

static IMPORT_C CMMFFormatDecode *NewL(MDataSource *aSource, const TDesC &aPreferredSupplier);

Description

Attempts to locate and instantiate a CMMFFormatDecode using data from MDataSource.

The data is expected to contain header data (from a file, stream or descriptor). Signatures (supplied by the plugin registry information) are sought in aSource.

Parameters

MDataSource *aSource

Header data. Must be derived from CMMFClip.

const TDesC &aPreferredSupplier

If this is provided, the list of matching plugins will be further searched for the latest version of a plugin supplied by the specified supplier.

Return value

CMMFFormatDecode *

If successful returns an instantiated CMMFFormatDecode from a plugin. If not successful, leaves with KErrNotFound.


NewL()

static IMPORT_C CMMFFormatDecode *NewL(const TDesC &aFileName, MDataSource *aSource, const TDesC &aPreferredSupplier, TBool &aSupportsCustomInterfaces);

Description

Parameters

const TDesC &aFileName

MDataSource *aSource

const TDesC &aPreferredSupplier

TBool &aSupportsCustomInterfaces

Return value

CMMFFormatDecode *


NewL()

static IMPORT_C CMMFFormatDecode *NewL(const TDesC8 &aSourceHeader, MDataSource *aSource, const TDesC &aPreferredSupplier, TBool &aSupportsCustomInterfaces);

Description

Attempts to locate and instantiate a CMMFFormatDecode using data in a buffer. The buffer is expected to contain header data (from a file, stream or descriptor).

Signatures (supplied by the plugin registry information) are sought in aSourceHeader.

This function uses the match string as a resolver parameter. The format base class uses the match string to find a match to the match string defined in the opaque_data field of the resource file. The match string would typically be a signature for a particular format usually defined in the format header.

Parameters

const TDesC8 &aSourceHeader

The data which is searched for matching signatures.

MDataSource *aSource

The controller's MDataSource and the source of the data for the format decode plugin.

const TDesC &aPreferredSupplier

If this is provided the list of matching plugins will be further searched for the latest version of a plugin supplied by the specified supplier.

TBool &aSupportsCustomInterfaces

Indicates whether the instantiated FormatDecode supports custom interfaces.

Return value

CMMFFormatDecode *

If successful returns an instantiated CMMFFormatDecode from a plugin. If not successful, leaves with KErrNotFound.


NewL()

static IMPORT_C CMMFFormatDecode *NewL(MDataSource *aSource, const TDesC &aPreferredSupplier, TBool &aSupportsCustomInterfaces);

Description

Attempts to locate and instantiate a CMMFFormatDecode using data from MDataSource.

The data is expected to contain header data (from a file, stream or descriptor). Signatures (supplied by the plugin registry information) are sought in aSource.

Parameters

MDataSource *aSource

Header data. Must be derived from CMMFClip.

const TDesC &aPreferredSupplier

If this is provided, the list of matching plugins will be further searched for the latest version of a plugin supplied by the specified supplier.

TBool &aSupportsCustomInterfaces

Indicates whether the instantiated FormatDecode supports custom interfaces.

Return value

CMMFFormatDecode *

If successful returns an instantiated CMMFFormatDecode from a plugin. If not successful, leaves with KErrNotFound.


~CMMFFormatDecode()

inline virtual ~CMMFFormatDecode();

Description

Destructor.


CMMFFormatDecode()

protected: inline CMMFFormatDecode();

Description

Default constructor

[Top]


Member functions


ImplementationUid()

inline TUid ImplementationUid() const;

Description

Returns the ECom plugin UID of this format.

Return value

TUid

The plugin UID.


Streams()

virtual TUint Streams(TUid aMediaType) const=0;

Description

Gets the number of streams of the specified media type.

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

Parameters

TUid aMediaType

The UID of the media type, for example KUidMediaTypeAudio or KUidMediaTypeVideo.

Return value

TUint

The number of streams of multimedia data in the format for the specified media type. For example, for a WAV or mp3 audio file this procedure would return 1 for a media type of audio and 0 for a media type of video. More complex multimedia formats (for example AVI and mp4) can support multiple streams of both video and audio.


FrameTimeInterval()

virtual TTimeIntervalMicroSeconds FrameTimeInterval(TMediaId aMediaType) const=0;

Description

Returns the time interval for one frame for the specified media type.

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

In the case of video, a frame would usually be one frame of video. In the case of audio, a frame may correspond to a frame of audio, if the particular audio data type is framed eg mp3. There are two definitions of a frame. A format frame, which may consist of several frames of a particular framed audio data type. This may be the case, for example for GSM610 (a low quality audio data type used in telephony) where a frame is only 65 bytes large. In this case a format frame consists of several GSM610 data type frames as passing the data out 65 bytes at a time would be inefficient. In the case of non-framed data such as pcm, a frame can be an arbitrary size determined by the format plugin.

Parameters

TMediaId aMediaType

The media type id.

Return value

TTimeIntervalMicroSeconds

The frame time interval


Duration()

virtual TTimeIntervalMicroSeconds Duration(TMediaId aMediaType) const=0;

Description

Returns the duration of the clip for the specified media type.

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

Parameters

TMediaId aMediaType

The media type ID.

Return value

TTimeIntervalMicroSeconds

The duration of the clip.


FillBufferL()

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

Description

Request from CMMFDataPath to fill the specified buffer. The CMMFFormat needs to break this down into one or more reads from the clip (from MDataSource - CMMFFormatDecode is a MDataSource to a CMMFDataPath consumer).

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

This method is the means by which data is obtained from the data source. aBuffer is the buffer that needs filling from the source data stream as identified by aMediaId. The format should read the frame number of the buffer via the buffer's CMMFBuffer::FrameNumber() method. 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 e.g. 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 i.e. 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 to fill.

MDataSink *aConsumer

The consumer.

TMediaId aMediaId

The media type ID.


CanCreateSourceBuffer()

inline virtual TBool CanCreateSourceBuffer();

Description

Tests whether a source buffer can be created.

The format knows what type of source buffer it requires so default returns ETrue. It doesn't usually need to set the size of this buffer.

Return value

TBool

A boolean indicating whether a buffer can be created. ETrue if the buffer can be created, EFalse otherwise.


CreateSourceBufferL()

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

Description

Creates a source buffer.

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

This function should create a buffer of length 0, the maximum length should be equal to the maximum possible frame size. In the case of non framed data it should be set to an arbitrary size, which is effectively a trade off between being too small which will affect performance as more source reads are required, and being too large which will give very coarse positioning granularity. For pcm data, a buffer size of 4K is a good compromise. The same compromise also applies when deciding to put multiple audio frames into one format frame. The sink buffer size may also effect the format buffer size and the controller may use this to suggest a buffer size to the format by calling the format's SuggestSourceBufferSize() method. Alternatively the MDataSource::CreateSourceBufferL() function that takes the additional aSinkBuffer parameter may also be used when deciding the source buffer maximum size of the created source buffer.

Parameters

TMediaId aMediaId

The media type ID.

TBool &aReference

If ETrue the MDataSource owns the buffer. If EFalse, then the caller owns the buffer. This should normally be set to EFalse as format plugins do not create the reference buffer.

Return value

CMMFBuffer *

The created source buffer.


SourceDataTypeCode()

virtual TFourCC SourceDataTypeCode(TMediaId aMediaId)=0;

Description

Returns the source data type code for the specified media type ID.

Used by the CMMFDataPath for codec matching.

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

Parameters

TMediaId aMediaId

The media type ID.

Return value

TFourCC

The source data type code.


BufferFilledL()

inline virtual void BufferFilledL(CMMFBuffer *aBuffer);

Description

Indicates the data source has filled the buffer.

Called by the CMMFFormat's MDataSource when it has filled the buffer. The default implementation below would need overriding in cases where multiple clip reads were required to fill the buffer from the data path.

Parameters

CMMFBuffer *aBuffer

The buffer to which the clip is added.


CanCreateSinkBuffer()

inline virtual TBool CanCreateSinkBuffer();

Description

Tests whether a sink buffer can be created.

Format would normally pass its own buffer onto the CMMFClip, so this may not be required. The default returns EFalse.

Return value

TBool

A boolean indicating if the sink buffer can be created. ETrue if buffer can be created, EFalse otherwise.


CreateSinkBufferL()

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

Description

Creates a sink buffer for the specified media ID. The default version returns NULL.

Parameters

TMediaId aMediaId

The media type ID.

TBool &aReference

If ETrue the MDataSink owns the buffer. If EFalse, then the caller owns the buffer.

Return value

CMMFBuffer *

The CMMFBuffer sink buffer.


SinkDataTypeCode()

inline virtual TFourCC SinkDataTypeCode(TMediaId aMediaId);

Description

Returns the sink data type code for the specified media type ID. This would be the same as the source data type four CC although the clip is not going to need this info.

Parameters

TMediaId aMediaId

The media type id.

Return value

TFourCC

The sink data type code.


GetNumberOfMetaDataEntriesL()

inline virtual void GetNumberOfMetaDataEntriesL(TInt &aNumberOfEntries);

Description

Gets the number of meta data entries.

Meta Data support. The decode format is only capable of reading meta data entries from the clip.

This is an optional method, used to return the number of meta data entries present in the format. A meta data entry is a format-specific field such as authorship, copyright, security details etc. The function is optional as many formats do not provide support for such additional meta data fields.

The default leaves with KErrNotSupported.

Parameters

TInt &aNumberOfEntries

A reference to the number of meta data entries supported by the format. On return, contains the number of meta data entries.


MetaDataEntryL()

inline virtual CMMFMetaDataEntry *MetaDataEntryL(TInt aIndex);

Description

Returns the specified meta data entry.

This method is optional as many formats do not provide support for such additional meta data fields.

The default leaves with KErrNotSupported.

Parameters

TInt aIndex

The zero based meta data entry index to retrieve.

Return value

CMMFMetaDataEntry *

The meta data entry.


SetNumChannels()

inline virtual TInt SetNumChannels(TUint aChannels);

Description

Sets the number of channels.

The default returns KErrNotSupported.

There would normally be no need to override this function as the format decode plugin can normally determine for itself the number of channels. It is only necessary to override this in cases where the format decode plugin cannot determine for itself the number of channels. This function should not be used if the audio clip already exists; that is, in the "Open and Append" scenario, when the function's behaviour is undefined.

Parameters

TUint aChannels

The number of channels.

Return value

TInt

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


SetSampleRate()

inline virtual TInt SetSampleRate(TUint aSampleRate);

Description

Sets the sample rate.

The default implementation returns KErrNotSupported.

There would normally be no need to override this function as the format decode can normally determine the sample rate for itself. It is only necessary to override this in cases where the format decode plugin cannot determine for itself the sample rate.

Parameters

TUint aSampleRate

The sample rate.

Return value

TInt

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


SetBitRate()

inline virtual TInt SetBitRate(TUint aBitRate);

Description

Sets the bit rate.

The default implementation returns KErrNotSupported.

This method is mainly provided for variable bit rate formats, such as mp3, where the bit rate can not be directly calculated from the sample rate. There would normally be no need to override this function as the format decode can normally determine the sample rate for itself. It is only necessary to override this in cases where the format decode plugin cannot determine for itself the sample rate.

Parameters

TUint aBitRate

The bit rate in bits per second.

Return value

TInt

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


NumChannels()

inline virtual TUint NumChannels();

Description

Returns the number of channels.

The default implementation returns 0.

Return value

TUint

The number of channels.


SampleRate()

inline virtual TUint SampleRate();

Description

Gets the sample rate.

The default implementation returns 0.

Return value

TUint

The sample rate.


BitRate()

inline virtual TUint BitRate();

Description

Gets the bit rate.

The default implementation returns 0.

This method is mainly provided for variable bit rate formats, such as mp3, where the bit rate can not be directly calculated from the sample rate. This function needs overriding for any format decode that supports audio.

Return value

TUint

The bit rate.


GetSupportedSampleRatesL()

inline virtual void GetSupportedSampleRatesL(RArray< TUint > &aSampleRates);

Description

Gets the supported sample rates.

The default implementation leaves with KErrNotSupported.

This should return an array of sample rates supported by the format where applicable. Note that this refers to the possible sample rates supported by the format, not the actual sample rate, which will be one of the supported sample rates. The implementation of this function is optional.

Parameters

RArray< TUint > &aSampleRates

Reference to an array of supported sample rates.


GetSupportedBitRatesL()

inline virtual void GetSupportedBitRatesL(RArray< TUint > &aBitRates);

Description

Gets the supported bit rates.

The default leaves with KErrNotSupported.

This should return an array of bit rates supported by the format where applicable. Note that this refers to the possible bit rates supported by the format, not the actual bit rate, which will be one of the supported bit rates. The implementation of this function is optional.

Parameters

RArray< TUint > &aBitRates

Reference to an array of supported bit rates.


GetSupportedNumChannelsL()

inline virtual void GetSupportedNumChannelsL(RArray< TUint > &aNumChannels);

Description

Gets the supported number of channels.

The default leaves with KErrNotSupported.

The implementation of this procedure should return an array of channels supported by the format where applicable. Note that this refers to the possible number of channels supported by the format, not the actual number of channels, which will be one of the supported channels. For example, for a format decode plugin capable of supporting mono and stereo the procedure would return an array of length two the first array member containing the value 1 and the second containing the value 2. The implementation of this function is optional.

Parameters

RArray< TUint > &aNumChannels

A reference to an array of supported number of channels.


GetSupportedDataTypesL()

inline virtual void GetSupportedDataTypesL(TMediaId aMediaId, RArray< TFourCC > &aDataTypes);

Description

Gets the supported data types for the given media type id.

The default leaves with KErrNotSupported.

The implementation of this procedure should return an array of data types supported by the format where applicable. Note that this refers to the possible data types that may be supported by the format, not the actual data type of the format, which will be one of the supported data types. For example, for a format decode plugin capable of supporting pcm16 and GSM610 the procedure would return an array of length two the first array member containing the fourCC code ' P16' and the second containing the value GSM6. The implementation of this function is optional.

Parameters

TMediaId aMediaId

The media type id.

RArray< TFourCC > &aDataTypes

A reference to an array of supported data types.


SuggestSourceBufferSize()

inline virtual void SuggestSourceBufferSize(TUint aSuggestedBufferSize);

Description

Used by the sink to suggest a source buffer size.

This is an optional function provided so that a controller can suggest a buffer size for the format. The controller should not assume that the format will accept the suggested buffer size and there is no obligation on behalf of the format to use the suggested buffer size.

Parameters

TUint aSuggestedBufferSize

A recommended buffer size that the format should create.


SetPositionL()

inline virtual void SetPositionL(const TTimeIntervalMicroSeconds &aPosition);

Description

Used to set the format's position.

Subsequent data reads should ignore the FrameNumber in the CMMFBuffer and use this setting to determine what data to provide.

The actual position the format sets itself may vary from this setting to ensure that it is aligned to the sample boundaries ensuring consistent data output.

If not supported, positional information should be extracted from the FrameNumber in CMMFBuffer

Parameters

const TTimeIntervalMicroSeconds &aPosition

The position the format should use.


PositionL()

inline virtual TTimeIntervalMicroSeconds PositionL();

Description

Supplies the current position.

Subsequent data reads will commence from this position.

Return value

TTimeIntervalMicroSeconds

The current position in microseconds.

[Top]


Member data


iClip

protected: MDataSource * iClip;

Description

The clip is the source for the decode format.


iDataPath

protected: MDataSink * iDataPath;

Description

The data path is the sink for the decode format.