IMediaObject::ProcessOutput method (mediaobj.h)

Article
4/26/2023

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The ProcessOutput method generates output from the current input data.

Syntax

HRESULT ProcessOutput(
            DWORD                  dwFlags,
            DWORD                  cOutputBufferCount,
  [in, out] DMO_OUTPUT_DATA_BUFFER *pOutputBuffers,
  [out]     DWORD                  *pdwStatus
);

Parameters

dwFlags

Bitwise combination of zero or more flags from the DMO_PROCESS_OUTPUT_FLAGS enumeration.

cOutputBufferCount

Number of output buffers.

[in, out] pOutputBuffers

Pointer to an array of DMO_OUTPUT_DATA_BUFFER structures containing the output buffers. Specify the size of the array in the cOutputBufferCount parameter.

[out] pdwStatus

Pointer to a variable that receives a reserved value (zero). The application should ignore this value.

Return value

Returns an HRESULT value. Possible values include those in the following table.

Return code	Description
E_FAIL	Failure
E_INVALIDARG	Invalid argument
E_POINTER	NULL pointer argument
S_FALSE	No output was generated
S_OK	Success

Remarks

The pOutputBuffers parameter points to an array of DMO_OUTPUT_DATA_BUFFER structures. The application must allocate one structure for each output stream. To determine the number of output streams, call the IMediaObject::GetStreamCount method. Set the cOutputBufferCount parameter to this number.

Each DMO_OUTPUT_DATA_BUFFER structure contains a pointer to a buffer's IMediaBuffer interface. The application allocates these buffers. The other members of the structure are status fields. The DMO sets these fields if the method succeeds. If the method fails, their values are undefined.

When the application calls ProcessOutput, the DMO processes as much input data as possible. It writes the output data to the output buffers, starting from the end of the data in each buffer. (To find the end of the data, call the IMediaBuffer::GetBufferAndLength method.) The DMO never holds a reference count on an output buffer.

If the DMO fills an entire output buffer and still has input data to process, the DMO returns the DMO_OUTPUT_DATA_BUFFERF_INCOMPLETE flag in the DMO_OUTPUT_DATA_BUFFER structure. The application should check for this flag by testing the dwStatus member of each structure.

If the method returns S_FALSE, no output was generated. However, a DMO is not required to return S_FALSE in this situation; it might return S_OK.

Discarding data:

You can discard data from a stream by setting the DMO_PROCESS_OUTPUT_DISCARD_WHEN_NO_BUFFER flag in the dwFlags parameter. For each stream that you want to discard, set the pBuffer member of the DMO_OUTPUT_DATA_BUFFER structure to NULL.

For each stream in which pBuffer is NULL:

If the DMO_PROCESS_OUTPUT_DISCARD_WHEN_NO_BUFFER flag is set, and the stream is discardable or optional, the DMO discards the data.
If the flag is set but the stream is neither discardable nor optional, the DMO discards the data if possible. It is not guaranteed to discard the data.
If the flag is not set, the DMO does not produce output data for that stream, but does not discard the data.

To check whether a stream is discardable or optional, call the IMediaObject::GetOutputStreamInfo method.

Requirements

Requirement	Value
Target Platform	Windows
Header	mediaobj.h (include Dmo.h)
Library	Dmoguids.lib

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