ILMUDPSrc Interface

This is the interface for the LEAD MPEG2 Transport UDP Source filter.

You can control this filter using this interface and by passing parameters to the UDP Source URL. See the UDP Source URL Syntax topic for more information on the URL parameters.

Interface Properties:

Type Name Description
IUnknown * CallbackObj The user callback that will be called when certain events occur. At the moment, there is only one event (EVENTTYPE_NODATAAVAILABLE), which indicates the UDP source has not received any data. You can use this callback to receive notifications indicating no data is arriving and cancel the wait.

The user callback object should implement the ILMSrcCallback interface.

LEADTOOLS uses this interface internally when you load a stream using the UDP source filter. The Play and Convert objects will automatically intercept the ILMSrcCallback  notifications and will send MediaEvent notifications to inform you when EVENTTYPE_NODATAAVAILABLE is fired by the UDP source. In other words, you do not need to implement the  ILMSrcCallback  interface to take advantage of this feature. See the Aborting Loading From The RTSP, ONVIF, and UDP Source Filters  topic for more information.

VARIANT_BOOL CallInSameThread Enables or disables the calling of the CallbackProc notifications in the same thread that set the ReceiveProcObj property.

Possible values are:

    Value Meaning
    VARIANT_TRUE Call the notifications in the same thread that set the callback. This reduces the performance and requires the application to process messages, otherwise the callback will not get called. It is the default and is required for platforms that have problem with multithreading, like VB 6.0 or dotnet.

This is the default.

    VARIANT_FALSE Call the notifications in any thread of the process. Use this setting for best performance in platforms that can handle this. This is the recommended mode for C++ applications. But you should be aware that your callback will not be called in the main thread, so you need to take care when you interact with the user interface.

Interface Methods:

HRESULT  GetReceiveTime(double offset, double *pReceiveTime);

Parameters

offset

Specifies the stream offset (in bytes) for which you want to get the receive time.

pReceiveTime

Pointer to a variable that will be updated with the receive time (in 100-nanosecond intervals since January 1, 1601 (UTC)).

Description

This method will return the time at which data for a certain stream offset has been received. The method will succeed only if logging has been enabled for this stream by passing the Logging=1 parameter to the URL. See the UDP Source URL syntax topic for more information on the URL syntax.

You will typically call this method to get the receive time at which the first key frame in the stream has been received. You can also call it to get the receive time for offset 0, but that might not be too useful since there is no guarantee that the data at offset 0 contains the first key frame in the stream. And using the receive time for offset 0 can induce slight errors in the calculations in situations in which the first key frame was received hundreds of milliseconds or even seconds after the initial data.

So it is recommended you call this method using the offset you received from ILMMpgDmx::StartStreamOffset, because that is the offset of the first key frame in the stream.

Once you have the receive time, you can convert it to a filename by using ConvertTimeToString. And you can convert the filename back to the receive time using ConvertStringToTime. Embedding the receive time into the filename allows you to preserve the receive time without the need for storing the value in an extra database through some other external means.

The receive time is in 100-ns units since January 1, 1601, equivalent to the FILETIME Windows API structure value. In .NET, you can convert this value using the DateTime.FromFileTime method.

To find out the difference in seconds between two ReceiveTime values, you can use this formula (commas were added to make it easier to see the number of zeros):

diff_in_seconds = (ReceiveTime1 - ReceiveTime2) / 10,000,000

Here is some pseudo-code showing you how you put all these together (error checking is ignored to make the code easier to understand):

void SetOutputFilenameAndStartConverting(IltmmConvert *pConvert) 
{ 
   // set the source URL with logging enabled (very important) 
   pConvert->put_SourceFile(L"udp://127.0.0.1:9005?Logging=1"); 
   pConvert->put_TargetFormat(ltmmCapture_TargetFormat_MPEG2_TRANSPORT); 
   pConvert->put_TargetFile(L""); /* set a dummy output file to build the graph */ 
   CComPtr pUnknown; 
   pConvert->GetSubObject(ltmmConvert_Object_SourceFilter, &pUnknown); 
   CComPtr pUDPSrc; 
   pUnknown->QueryInterface(IID_ILMUDPSrc, (void **)&pUDPSrc); 
   pUnknown.Release(); 
   pConvert->GetSubObject(ltmmConvert_Object_Splitter, &pUnknown); 
   CComPtr pDmx; 
   pUnknown->QueryInterface(IID_ILMMpgDmx, (void **)&pDmx); 
   double startOffset; 
   pDmx->get_StartStreamOffset(&startOffset); /* get the start offset */ 
   double receiveTime; 
   pUDPSrc->GetReceiveTime(startOffset, &receiveTime); /* get the receive time */ 
   pUDPSrc->StopLogging(); /* stop logging now that I have the receive start time */ 
   BSTR outputFilename; 
   pUDPSrc->ConvertTimeToString(receiveTime, L"c:\\output\\", L".mpg", &outputFilename); 
   pConvert->put_TargetFile(outputFilename); /* set the real output filename */ 
   SysFreeString(outputFilename); /* free the string returned by ConvertTimeToString */ 
   pConvert->StartConvert(); 
} 

Returns

S_OK if successful, < 0 if an error occurred.

Common Error Codes

LTMM_E_LOGGING_NOT_STARTED

Logging was not enabled (you did not pass "?Logging=1" to the UDP URL).

HRESULT  ConvertTimeToString(double receiveTime, BSTR pszPrefix, BSTR pszSuffix, BSTR *pRet);

Parameters

receiveTime

The receive time, in 100ns units since January 1, 1601 (UTC) (as obtained from GetReceiveTime).

pszPrefix

Optional string containing the prefix (usually the folder where you will store the output file).

pszSuffix

Optional string containing the suffix (usually the file extension).

pRet

Pointer to a variable that will be updated with the string. The value returned should be freed using the SysFreeString windows API function.

Description

Use this method to convert a receive time obtained from GetReceiveTime. Convert the string back to the receive time using the ConvertStringToTime method. The string returned by this function will be as follows:

<pszPrefix>YYYY_MM_DD__hh_mm_ss_fff<pszSuffix>

Where <pszPrefix> and <pszSuffix> are the valued passed as parameters, YYYY, MM and DD represent the date (year using 4-digits, month and day using 2 digits) and hh, mm and ss are the time (hours, minutes, seconds using 2 digits) and fff are milliseconds using 3 digits.

Returns

S_OK if successful, < 0 if an error occurred.

Common Error Codes

E_POINTER

pRet is invalid (NULL)

E_OUTOFMEMORY

There is not enough memory to allocate the resulting string.

HRESULT  ConvertStringToTime(BSTR pszString, double *pReceiveTime);

Parameters

pszString

The string as returned by ConvertTimeToString.

pReceiveTime

Pointer to a variable that will be updated with the receive time, in 100ns units since January 1, 1601 (UTC).

Description

Use this method to convert a string obtained from ConvertTimeToString back to the value returned by GetReceiveTime.

The source string passed to the function should have the following format, (otherwise the method will fail):

<pszPrefix>YYYY_MM_DD__hh_mm_ss_fff<pszSuffix>

<pszPrefix> and <pszSuffix> will be ignored and the time will be reconstructed using the time indicated by YYYY, MM, DD, hh, mm, ss and fff.

See GetReceiveTime for more information on how to convert the receive time to other values that might be useful.

Returns

S_OK if successful, < 0 if an error occurred.

Common Error Codes

E_POINTER

pRet or pReceiveTime are invalid (NULL)

E_INVALIDARG

The pszString value is not formatted correctly. Make sure it is the same value returned by ConvertTimeToString.

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