前面我們說了文件的打開，發送數據給下一個peer，但是我們還是不明白文件的格式是 如何識別的，因爲文件的種類繁多，文件的識別就會很麻煩，並且還要考慮到可擴展性，所以這個文件的識別是以插件的形式來存在的，這裏我們簡要的說一下，這 個插件的框架。
由於文件的格式很多，而且標準也很多，很難 肯定某一文件就是某種的格式，因而就引入一個確信度的概念。
typedef Oscl_Vector<OSCL_HeapString<OsclMemAllocator>, OsclMemAllocator> PVMFRecognizerMIMEStringList;
typedef enum _PVMFRecognizerConfidence
{
PVMFRecognizerConfidenceNotCertain, // 100% sure not the format
PVMFRecognizerConfidenceNotPossible, // Maybe not the format
PVMFRecognizerConfidenceUnknown, // Not sure one way or the other
PVMFRecognizerConfidencePossible, // Maybe the format
PVMFRecognizerConfidenceCertain // 100% sure of the format
} PVMFRecognizerConfidence;
然後是文件識別的結果：
class PVMFRecognizerResult
{
public:
PVMFRecognizerResult()
{
};
// Copy constructor for use in Oscl_Vector
PVMFRecognizerResult(const PVMFRecognizerResult& aSrc)
{
iRecognizedFormat = aSrc.iRecognizedFormat;
iRecognitionConfidence = aSrc.iRecognitionConfidence;
// iRecognizerSubFormatList=aSrc.iRecognizerSubFormatList;
};
~PVMFRecognizerResult()
{
};
// The format of interest as a MIME string
OSCL_HeapString<OsclMemAllocator> iRecognizedFormat;
// The confidence level of recognition
PVMFRecognizerConfidence iRecognitionConfidence;
// If the format is a container format, the format of content within
// Oscl_Vector<PVMFRecognizerResult, OsclMemAllocator> iRecognizerSubFormatList;
};
格式和確信度。
然後就是一個事件的監控者Observer。
/**
* PVMFRecognizerCommmandHandler Class
*
* PVMFRecognizerCommmandHandler is the PVMF Recognizer observer class for notifying the
* status of asynchronous requests. The API provides a mechanism for the status of each
* command to be passed back along with context specific information where applicable.
* User of the recognizer registry must have a class derived from PVMFNodeCmdStatusObserver
* and implement the pure virtual function in order to receive event notifications from
* PVMF Recognizer Registry.
**/
class PVMFRecognizerCommmandHandler
{
public:
/**
* Handle an event that has been generated.
*
* @param aResponse
* The response to a previously issued command
*/
virtual void RecognizerCommandCompleted(const PVMFCmdResp& aResponse) = 0;
virtual ~PVMFRecognizerCommmandHandler() {}
};
#endif // PVMF_RECOGNIZER_TYPES_H_INCLUDED
這些都只是純虛類。
文件識別，一 般都是讀取文件中的某些特殊的字節，然後才能做判斷的，由於不同的文件讀取的地方不同，並且識別的規則也是不同，所以定義一個基本的接口。
class PVMFRecognizerPluginInterface
{
public:
/**
* Virtual destructor for the plug-in. All plug-ins should perform any clean up here
**/
virtual ~PVMFRecognizerPluginInterface()
{
};
/**
* This methods returns a list of format(s) that this plug-in can recognize. Each supported format
* is represented by a MIME string.
*
* @param aSupportedFormatsList
* Reference to a list of MIME strings which will be filled in with list of formats that the plug-in can recognize.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for the format list
*
* @returns A PVMF status code to report result of method
**/本插件支持下面的一些 格式的識別，以一個列表的形式返回
注意我們的文件識別都是以 插件的形式存在的，這樣就可以保證文件識別的可擴展性，每一個插件都必須從這個接口來繼承，另外還必須有一個類統一管理這些插件，如插件的查找和註冊
virtual PVMFStatus SupportedFormats(PVMFRecognizerMIMEStringList& aSupportedFormatsList) = 0;
/**
* This method determines the the specified content is or is not one of the formats recognized by this plug-in
*
* @param aSourceDataStreamFactory
* A reference to a PVMFDataStreamFactory representing the content to recognize
* @param aFormatHint
* An optional input parameter expressed as a list of MIME string which provides a priori hint for the format
* of the content specified by aSourceDataStreamFactory.
* @param aRecognizerResult
* An output parameter which is a reference to a vector of PVMFRecognizerResult that will contain the recognition
* result if the Recognize() method succeeds.
*
* @exception This method can leave with one of the following error codes
*
* @returns A PVMF status code to report result of method
**/
//給定一個數據源讓你去識別，有一個優先考慮的格式列表參數，返回的是 一個識別結果的列表，列出可能的格式和確信度。
virtual PVMFStatus Recognize(PVMFDataStreamFactory& aSourceDataStreamFactory,
PVMFRecognizerMIMEStringList* aFormatHint,
Oscl_Vector<PVMFRecognizerResult, OsclMemAllocator>& aRecognizerResult) = 0;
/**
* This method returns the mininum required bytes in datastream for this plug-in
* to be able to recognize its supported formats.
*
* @param aBytes[out]
* A reference to a minimum required bytes
*
* @returns A PVMF status code to report result of method.
* PVMFSuccess in case of success and PVMFFailure otherwise.
**///或者識別所需的最小字節數
virtual PVMFStatus GetRequiredMinBytesForRecognition(uint32& aBytes) = 0;
};
每一個插件都 需要佔用一定內存，因而就有下面的定義：一個插件的工廠的基類，每一個插件都要有一個這樣的工廠接口來創建和刪除某一個插件。
/**
* An abstract base class to create and destroy a recognizer plug-in. Every recognizer plug-in should have
* an associated factory class to provide a standard way to create and destroy the plug-in.
**/
class PVMFRecognizerPluginFactory: public HeapBase
{
public:
/**
* Virtual destructor for the plug-in factory. All plug-in factory should perform any clean up here
**/
virtual ~PVMFRecognizerPluginFactory()
{
};
/**
* This method instantiates and returns the recognizer plug-in that the factory is associated with.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for the recognizer plug-in
* @returns A pointer to the recognizer plug-in instance if creation is successful.
**/
virtual PVMFRecognizerPluginInterface* CreateRecognizerPlugin() = 0;
/**
* This method destroys the specified recognizer plug-in pointer as the particular recognizer plug-in
* the factory is associated with.
*
* @param aPlugIn
* A pointer to the recognizer plug-in that should be destroyed.
*
* @exception This method can leave with one of the following error codes
*
* @returns None
**/
virtual void DestroyRecognizerPlugin(PVMFRecognizerPluginInterface* aPlugIn) = 0;
};
然後就是一個 模板的定義，因爲插件很多，這裏我們寫一個簡單的模板：
/**
* Basic templatized recognizer plug-in factory. Can be used if the recognizer plug-in only needs
* to be instantiated and destroyed by just new and delete, respectively and no other functionality
* is needed from the factory class.
**/
template<class T>
class PVMFRecognizerPluginFactoryBasic : public PVMFRecognizerPluginFactory
{
public:
virtual ~PVMFRecognizerPluginFactoryBasic()
{
};
PVMFRecognizerPluginInterface* CreateRecognizerPlugin()
{
T* plugin = OSCL_NEW(T, ());
return plugin;
};
void DestroyRecognizerPlugin(PVMFRecognizerPluginInterface* aPlugIn)
{
T* plugin = (T*)aPlugIn;
OSCL_DELETE(plugin);
};
};
這樣關於插件的基類，我們基本搞定，下面的就是這麼多插件在一起如何去管理。這裏就是一個靜態類（static）。負責插件的註冊和註銷，並且負責文件的的尋找，來了文件，歷遍所有註冊過的插件來找到最匹配的格式。這和微軟的DirectShow框架極爲相似，不過微軟的Filter是這側到註冊表裏面去了，並且，微軟Filter的概念不僅僅是文件的識別，在微軟的註冊表中，有一項就是Media Type，規定了系統所能夠識別的文件類型，每一個類型都要有匹配碼，例如前面 八個字節是什麼，後面四個字節是什麼，這些都是在註冊表中，註冊的另外的一個就是打開這個文件所需的Source Filter的ID，這樣要播放的文件的時候按照一定優先級匹配這些註冊信息就行了。
這裏關於插件 的管理有一個單獨的靜態類，靜態類的特點就是不管類是不是存在，這個東西都是存在的，並且全局可訪問。這纔是我們識別的關鍵代碼：
/**
* A class of static methods that provides the interface to the PVMF recognizer registry..
* With these static methods, the recognizer registry can be initialized and shutdown, recognizer
* plug-ins can be registered and unregistered, and format of a content can be recognized.
**/
class PVMFRecognizerRegistry
{
public:
/**
格式的註冊信息的初始化， 因爲我們知道，一種格式的識別，都會註冊相應的信息，識別器就是通過這些信息的歷遍，找出對應的文件。在使用識別器之前，最先就是初始化。
* This static method initializes the recognizer registry for use. This method must be called once
* and succeed before calling any other methods from PVMFRecognizerRegistry.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for the registry implementation
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus Init();
/**
使用完之後， 就要清空
* This static methods shuts down and cleans up the recognizer registry. This method must be called once
* after there is no more use for the recognizer registry to properly release the memory allocated for the
* registry
**/
OSCL_IMPORT_REF static void Cleanup();
/**
一種媒體格式識別信息的添 加，實際上就是添加一個PVMFRecognizerPluginFactory，前面我們說過每一種格式都會有其對應的PVMFRecognizerPluginFactory。
* This static method adds the specified recognizer plug-in factory to the list of available recognizers.
* The passed-in plug-in factory would be used to create and destroy the recognizer plug-in in the Recognize() methods.
* The passed-in plug-in factory reference must be valid until it is removed from the list by the RemovePlugin() method.
*
* @param aPluginFactory
* A reference to a recognizer plug-in factory to add to the list of registered recognizers
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for vector holding the plug-in factory pointers
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus RegisterPlugin(PVMFRecognizerPluginFactory& aPluginFactory);
/** 註銷某一種格式，將某一種識別的信息從註冊信息列表中剔除
* This static method removes the specified recognizer plug-in factory from the list of available recognizers.
* The passed-in plug-in factory must have been added before with RegisterPlugin() for this method to succeed.
* After the plug-in factory is successfully removed, the factory instance can be deleted.
*
* @param aPluginFactory
* A reference to a recognizer plug-in factory to remove from the list of registered recognizers
*
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus RemovePlugin(PVMFRecognizerPluginFactory& aPluginFactory);
/**
* This static method creates a recognition session with the recognizer framework.
*創建一個識別的會話，
* @param aSessionId 返回一個會話的ID
* A reference to a PVMFSessionId which will be set to the session's unique identifier when this method
* completes successfully.
* @param aCmdHandler 給它一個識別的觀察者，也就是消息的監控者
* A reference to a PVMFRecognizerCommmandHandler which will receive asynchronous command completion notification.
*
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus OpenSession(PVMFSessionId& aSessionId, PVMFRecognizerCommmandHandler& aCmdHandler);
/**
* This static method shuts down a recognition session with the recognizer framework.
*關閉一個會話
* @param aSessionId
* The unique identifier of the session to close
*
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus CloseSession(PVMFSessionId aSessionId);
/**開始識別，開始識別的開始就需要一個數據的來源、然後是優先考慮的格 式、識別結果的存儲、
* This static method asynchronously determines the format of the specified content using the currently registered
* recognizer plug-ins. When the recognizer request completes, the user would be notified via the PVMFRecognizerCommandHandler
* callback handler set when opening the session.
*
* @param aSessionId
* The unique identifier for the recognizer session
* @param aSourceDataStreamFactory 數據的來源
* A reference to a PVMFDataStreamFactory representing the content to recognize
* @param aFormatHintList優先考慮的格式
* An optional input parameter expressed as a list of MIME string which provides a priori hint for the format
* of the content specified by aSourceDataStreamFactory.
* @param aRecognizerResult結果的存儲
* An output parameter which is a reference to a vector of PVMFRecognizerResult that will contain the recognition
* result if the Recognize() method succeeds.
* @param aCmdContext
* Optional pointer to opaque data that will be returned in the command completion response，識別上下文的返回
* @param aTimeout 識別的時間限制
* Optional timeout value for the recognition request. If the recognition operation takes more time than the timeout
* value, the operation will be cancelled with PVMFErrTimeout status code. If the timeout value is set to 0, the
* recognition operation will go to completion.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot allocated to process this request
* OsclErrArgument if one or more of the passed-in parameters is invalid
*
* @returns A PVMF command ID for the recognize request
**/
OSCL_IMPORT_REF static PVMFCommandId Recognize(PVMFSessionId aSessionId, PVMFDataStreamFactory& aSourceDataStreamFactory, PVMFRecognizerMIMEStringList* aFormatHintList,
Oscl_Vector<PVMFRecognizerResult, OsclMemAllocator>& aRecognizerResult, OsclAny* aCmdContext = NULL, uint32 aTimeout = 0);
/**取消前一個異步的識別操作
* This static method cancels a previously issued asynchronous request that hasn't completed yet.
*
* @param aSessionId
* The unique identifier for the recognizer session
* @param aCommandToCancelId
* Unique identifier for the asynchronous request to cancel.
* @param aCmdContext
* Optional pointer to opaque data that will be returned in the command completion response
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot allocated to process this request
* OsclErrArgument if one or more of the passed-in parameters is invalid
*
* @returns A PVMF command ID for the cancel request
**/
OSCL_IMPORT_REF static PVMFCommandId CancelCommand(PVMFSessionId aSessionId, PVMFCommandId aCommandToCancelId, OsclAny* aCmdContext = NULL);
};
這樣我們的識 別文件格式的框架就完成了。下面看一些具體的實現。
很遺憾，在OSDL中，我們已經定義好了一個類似於微軟註冊表的東西，它存在與OSDL中，在OSDL之上的任何代碼都是可以訪問的。
class OsclTLSRegistry
{
public:
/*
** Get an entry
** @param ID: identifier
** @param error (output) 0 for success or an error from TPVBasePanicEnum
** @returns: the entry value
*/
OSCL_IMPORT_REF static OsclAny* getInstance(uint32 ID, int32 &error);
/*
** Set an entry
** @param ID: identifier
** @param error (output) 0 for success or an error from TPVBasePanicEnum
** @returns: the entry value
*/
OSCL_IMPORT_REF static void registerInstance(OsclAny* ptr, uint32 ID, int32 &error);
private:
OsclTLSRegistry()
{}
typedef OsclAny* registry_type;
typedef registry_type* registry_pointer_type;
#if ( OSCL_TLS_IS_KEYED)
class TKeyItem
{
public:
TKeyItem(): iTlsKey(NULL), iThreadId(0)
{}
TOsclTlsKey *iTlsKey;
TOsclTlsThreadId iThreadId;
};
class TlsKeyTable
{
public:
TlsKeyTable(): iNumKeys(0)
{}
_OsclBasicLock iLock;
uint32 iNumKeys;
TKeyItem iKeys[OSCL_TLS_MAX_THREADS];
};
//The key table is a global variable.
static TlsKeyTable* iTlsKeyTable;
static void GetThreadId(TOsclTlsThreadId &threadId, int32&);
static TOsclTlsKey* LookupTlsKey(int32&);
static bool SaveTlsKey(TOsclTlsKey* key, int32&);
static bool RemoveTlsKey(Oscl_DefAlloc& alloc, TOsclTlsKey* key, int32&);
#endif
private:
OSCL_IMPORT_REF static void initialize(Oscl_DefAlloc &alloc, int32 &error);
OSCL_IMPORT_REF static void cleanup(Oscl_DefAlloc &alloc, int32 &error);
friend class OsclBase;
};
這個類的實現 可以參見具體的代碼，所以這裏我們就不去多說。這裏我們在註冊信息中填入的是一個什麼呢？
我們看靜態的 初始化函數。
OSCL_EXPORT_REF PVMFStatus PVMFRecognizerRegistry::Init()
{
// Check that there is no existing registry
PVMFRecognizerRegistryImpl* pvrecregimpl = OSCL_STATIC_CAST(PVMFRecognizerRegistryImpl*, PVMFRECOGNIZER_REGISTRY::getInstance(PVMFRECOGNIZER_REGISTRY_ID));
// 如果存在，那麼我就不用註冊這個一項了
if (pvrecregimpl != NULL)
{
// Registry is already present so no need to instantiate again
// Just increment the refcount
(pvrecregimpl->iRefCount)++;
return PVMFSuccess;
}
// Instantiate the registry implementation，否則就開始分配新的空間開始註冊
Oscl_TAlloc<PVMFRecognizerRegistryImpl, OsclMemAllocator> talloc;
pvrecregimpl = OSCL_ALLOC_NEW(talloc, PVMFRecognizerRegistryImpl, ());
// Save it on singleton or TLS
PVMFRECOGNIZER_REGISTRY::registerInstance(pvrecregimpl, PVMFRECOGNIZER_REGISTRY_ID);
return PVMFSuccess;
}
繼續往下面講之前，我覺得我們可以看一下PVMFRecognizerRegistryImpl，這個是怎麼實現的，PVMFRecognizerRegistryImpl是我們註冊表中保存的一個東東。主要實現文件的識別，包含很多的信息。我以前以爲只有變量才能註冊 的，其實函數也能註冊的，函數代碼的空間也是數據，是數據就有指針，所以整個類也是可以註冊的。註冊後，如果要清空，那麼就要調用Cleanup，
OSCL_EXPORT_REF void PVMFRecognizerRegistry::Cleanup()
{
// Retrieve the registry implementation instance from singleton or TLS and destroy it
首先單件模式，返回我們註冊的PVMFRecognizerRegistryImpl指針，這個指針指向的內容是存在的，因爲我們前面在初始化的時候就分 配了內存
PVMFRecognizerRegistryImpl* pvrecregimpl = OSCL_STATIC_CAST(PVMFRecognizerRegistryImpl*, PVMFRECOGNIZER_REGISTRY::getInstance(PVMFRECOGNIZER_REGISTRY_ID));
if (pvrecregimpl != NULL)
{
// First decrement the refcount， 直接自減就行了，自身負責分配
--(pvrecregimpl->iRefCount);
// If the resulting refcount is 0, then delete the instance
if ((pvrecregimpl->iRefCount) <= 0)
{
Oscl_TAlloc<PVMFRecognizerRegistryImpl, OsclMemAllocator> talloc;
OSCL_ALLOC_DELETE(pvrecregimpl, talloc, PVMFRecognizerRegistryImpl);
// Unregister by putting NULL pointer in singleton or TLS 釋放後，注意把註冊表中的信息清空
PVMFRECOGNIZER_REGISTRY::registerInstance(NULL, PVMFRECOGNIZER_REGISTRY_ID);
}
}
else
{
// Registry has already been cleaned up so nothing to do
}
}
然後就是註冊我們的文件識別組件
OSCL_EXPORT_REF PVMFStatus PVMFRecognizerRegistry::RegisterPlugin(PVMFRecognizerPluginFactory& aPluginFactory)
{
PVMFRecognizerRegistryImpl* pvrecregimpl = OSCL_STATIC_CAST(PVMFRecognizerRegistryImpl*, PVMFRECOGNIZER_REGISTRY::getInstance(PVMFRECOGNIZER_REGISTRY_ID));
if (pvrecregimpl != NULL)
{
return pvrecregimpl->RegisterPlugin(aPluginFactory);
}
else
{
// Registry hasn't been initialized yet. Assert
OSCL_ASSERT(false);
return PVMFErrNotReady;
}
}
其實很簡單，調用對應的成員就行了。
下面的幾個函數基本上都是這樣子了，RemovePlugin、OpenSession、CloseSession、Recognize、CancelCommand。
下面我們看看
PVMFRecognizerRegistryImpl的實現。
因爲文件的識別是一個比較“卡”的過程，爲 了不讓我們的軟件給人很卡的感官，我們這裏把這個類另闢一個線程來進行，並且以異步的方式來調用，通過命令。
識別的命令有下面的兩種類型：
/**
* PVMFRecRegImplCommandType enum
*
* Enumeration of commands that can be issued to the PVMF Recognizer Registry
*
**/
typedef enum
{
PVMFRECREG_COMMAND_RECOGNIZE = 1,
PVMFRECREG_COMMAND_CANCELCOMMAND,
} PVMFRecRegImplCommandType;
一個就是開始識別，一個就是取消識別。
class PVMFRecRegSessionInfo
{
public:
PVMFRecRegSessionInfo()
{
};
PVMFRecRegSessionInfo(const PVMFRecRegSessionInfo& aSrc)
{
iRecRegSessionId = aSrc.iRecRegSessionId;
iRecRegCmdHandler = aSrc.iRecRegCmdHandler;
};
~PVMFRecRegSessionInfo()
{
};
PVMFSessionId iRecRegSessionId;
PVMFRecognizerCommmandHandler* iRecRegCmdHandler;
};
識別的一個信 息的保存，一個事識別的sessionID，一個事事件處理。
下面就是一個 命令的具體的封裝，包含一個參數的列表/**
* PVMFRecRegImplCommand Class
*
* PVMFRecRegImplCommand class is a data class to hold issued commands inside the recognizer registry impl
**/
class PVMFRecRegImplCommand
{
public:
/**
* The constructor for PVMFRecRegImplCommand which allows the data values to be set.
*
* @param aCmdType The command type value for this command.
* @param aCmdId The command ID assigned for this command.
* @param aContextData The pointer to the passed-in context data for this command.
* @param aParamVector The optional pointer to a list of parameters
*
* @returns None
**/初始化就是一個參數 列表
PVMFRecRegImplCommand(PVMFSessionId aSessionId, int32 aCmdType, PVMFCommandId aCmdId, OsclAny* aContextData = NULL,
Oscl_Vector<PVMFRecRegImplCommandParamUnion, OsclMemAllocator>* aParamVector = NULL, bool aAPICommand = true) :
iSessionId(aSessionId), iCmdType(aCmdType), iCmdId(aCmdId), iContextData(aContextData), iAPICommand(aAPICommand)
{
iParamVector.clear();
if (aParamVector)
{
iParamVector = *aParamVector;
}
}
/**
* The copy constructor for PVMFRecRegImplCommand. Used mainly for Oscl_Vector.
*
* @param aCmd The reference to the source PVMFRecRegImplCommand to copy the data values from.
*
* @returns None
**/
PVMFRecRegImplCommand(const PVMFRecRegImplCommand& aCmd)
{
iSessionId = aCmd.iSessionId;
iCmdType = aCmd.iCmdType;
iCmdId = aCmd.iCmdId;
iContextData = aCmd.iContextData;
iAPICommand = aCmd.iAPICommand;
iParamVector = aCmd.iParamVector;
}
/**
* This function returns the session ID for the command
*
* @returns The session ID value for this command.
**/
PVMFSessionId GetSessionId()const
{
return iSessionId;
}
/**
* This function returns the stored command type value.
*
* @returns The signed 32-bit command type value for this command.
**/
int32 GetCmdType()const
{
return iCmdType;
}
/**
* This function returns the stored command ID value.
*
* @returns The PVMFCommandId value for this command.
**/
PVMFCommandId GetCmdId()const
{
return iCmdId;
}
/**
* This function returns the stored context data pointer.
*
* @returns The pointer to the context data for this command
**/
OsclAny* GetContext()const
{
return iContextData;
}
/**
* This function tells whether the command is an API command or not
*
* @returns true if API command, false if not.
**/
bool IsAPICommand()const
{
return iAPICommand;
}
/**
* This function returns the command parameter from the specified index.
* If the specified index is not available, empty parameter will be returned
*
* @param aIndex The index of the parameter to return
*
* @returns The stored parameter for this command
**/
PVMFRecRegImplCommandParamUnion GetParam(uint32 aIndex)const
{
if (aIndex >= iParamVector.size())
{
PVMFRecRegImplCommandParamUnion param;
oscl_memset(¶m, 0, sizeof(PVMFRecRegImplCommandParamUnion));
return param;
}
else
{
return iParamVector[aIndex];
}
}
bool operator==(const PVMFRecRegImplCommand& x)const
{
return iCmdId == x.iCmdId;
}
PVMFSessionId iSessionId;
int32 iCmdType;
PVMFCommandId iCmdId;
OsclAny* iContextData;
bool iAPICommand;
Oscl_Vector<PVMFRecRegImplCommandParamUnion, OsclMemAllocator> iParamVector;
};
上面就是一個帶參數的識別命令。
然後有一個優先級的比較：
class PVMFRecRegImplCommandCompareLess
{
public:
/**
* The algorithm used in OsclPriorityQueue needs a compare function
* that returns true when A's priority is less than B's
* @return true if A's priority is less than B's, else false
*/
int compare(PVMFRecRegImplCommand& a, PVMFRecRegImplCommand& b) const
{
int a_pri = PVMFRecRegImplCommandCompareLess::GetPriority(a);
int b_pri = PVMFRecRegImplCommandCompareLess::GetPriority(b);
if (a_pri < b_pri)
{
// Higher priority
return true;
}
else if (a_pri == b_pri)
{
// Same priority so look at the command ID to maintain FIFO
return (a.GetCmdId() > b.GetCmdId());
}
else
{
// Lower priority
return false;
}
}
/**
* Returns the priority of each command
* @return A 0-based priority number. A lower number indicates lower priority.
*/
static int GetPriority(PVMFRecRegImplCommand& aCmd)
{
switch (aCmd.GetCmdType())
{
case PVMFRECREG_COMMAND_RECOGNIZE:
return 5;
case PVMFRECREG_COMMAND_CANCELCOMMAND:
return 3;
default:
return 0;
}
}
};
如何識別的？
/**
* Implementation of the recognizer registry. The recognizer interface class should only
* use this class.
**/
這裏爲什麼要 從PvmiDataStreamObserver來繼承，因爲我們的識別就必須讀取一部分的字節，必然會有相關的data數據流的操作，這裏是一個簡單的事件監控。爲什麼要從OsclTimerObject，因爲我們識別是單開線程的，並且識別有一個時間的上線。
class PVMFRecognizerRegistryImpl : public OsclTimerObject,
public PvmiDataStreamObserver
{
public:
PVMFRecognizerRegistryImpl();
~PVMFRecognizerRegistryImpl();
註冊和註銷識 別插件
PVMFStatus RegisterPlugin(PVMFRecognizerPluginFactory& aPluginFactory);
PVMFStatus RemovePlugin(PVMFRecognizerPluginFactory& aPluginFactory);
PVMFStatus OpenSession(PVMFSessionId& aSessionId, PVMFRecognizerCommmandHandler& aCmdHandler);
PVMFStatus CloseSession(PVMFSessionId aSessionId);
識別
PVMFCommandId Recognize(PVMFSessionId aSessionId, PVMFDataStreamFactory& aSourceDataStreamFactory, PVMFRecognizerMIMEStringList* aFormatHint,
Oscl_Vector<PVMFRecognizerResult, OsclMemAllocator>& aRecognizerResult, OsclAny* aCmdContext, uint32 aTimeout);
PVMFCommandId CancelCommand(PVMFSessionId aSessionId, PVMFCommandId aCommandToCancelId, OsclAny* aCmdContext);
// Reference count for the registry implementation
int32 iRefCount; 註冊的Plug個數
private:
這個我懷疑是這樣的，同時可能有多個識別的操作，那麼就需要列表處理
PVMFSessionId iNextSessionId;
PVMFCommandId iNextCommandId;
// From OsclTimerObject
void Run();
// Vector to hold the active sessions
Oscl_Vector<PVMFRecRegSessionInfo, OsclMemAllocator> iRecognizerSessionList;
// Vector to hold the available recognizer plug-in
Oscl_Vector<PVMFRecognizerPluginFactory*, OsclMemAllocator> iRecognizerPluginFactoryList;
int32 FindPluginFactory(PVMFRecognizerPluginFactory& aFactory);
PVMFRecognizerPluginInterface* CreateRecognizerPlugin(PVMFRecognizerPluginFactory& aFactory);
void DestroyRecognizerPlugin(PVMFRecognizerPluginFactory& aFactory, PVMFRecognizerPluginInterface* aPlugin);
// Vector to hold pending, current, and to-cancel commands
OsclPriorityQueue<PVMFRecRegImplCommand, OsclMemAllocator, Oscl_Vector<PVMFRecRegImplCommand, OsclMemAllocator>, PVMFRecRegImplCommandCompareLess> iRecognizerPendingCmdList;
Oscl_Vector<PVMFRecRegImplCommand, OsclMemAllocator> iRecognizerCurrentCmd;
Oscl_Vector<PVMFRecRegImplCommand, OsclMemAllocator> iRecognizerCmdToCancel;
PVMFCommandId AddRecRegCommand(PVMFSessionId aSessionId, int32 aCmdType, OsclAny* aContextData = NULL, Oscl_Vector<PVMFRecRegImplCommandParamUnion, OsclMemAllocator>* aParamVector = NULL, bool aAPICommand = true);
void CompleteCurrentRecRegCommand(PVMFStatus aStatus, const uint32 aCurrCmdIndex = 0, PVInterface* aExtInterface = NULL);
bool FindCommandByID(Oscl_Vector<PVMFRecRegImplCommand, OsclMemAllocator> &aCmdQueue, const PVMFCommandId aCmdId);
// Command handling functions
void DoRecognize();
void CompleteRecognize(PVMFStatus aStatus);
void DoCancelCommand(PVMFRecRegImplCommand& aCmd);
PVMFDataStreamFactory* iDataStreamFactory;
PVMIDataStreamSyncInterface* iDataStream;
PvmiDataStreamSession iDataStreamSessionID;
PvmiDataStreamCommandId iRequestReadCapacityNotificationID;
PVMFStatus GetMaxRequiredSizeForRecognition(uint32& aMaxSize);
PVMFStatus GetMinRequiredSizeForRecognition(uint32& aMinSize);
PVMFStatus CheckForDataAvailability();
//logger
PVLogger* iLogger;
/* From PvmiDataStreamObserver */
void DataStreamCommandCompleted(const PVMFCmdResp& aResponse);
void DataStreamInformationalEvent(const PVMFAsyncEvent& aEvent);
void DataStreamErrorEvent(const PVMFAsyncEvent& aEvent);
bool oRecognizePending;
PVMFStatus iDataStreamCallBackStatus;
};
這個函數具體是如何實現的，有興趣的可以繼續看一下，我小看了一下，基本上就是一個for循環識別文件的格式。並且這種框架 很容易擴展新的文件格式。
Opencore之文件解析
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