Export (0) Print
Expand All

CMediaSample class

CMediaSample Class Hierarchy

The CMediaSample class defines a media sample that supports the IMediaSample2 interface. The media sample contains a pointer to a memory buffer, and various properties stored as protected member variables.

Media samples are created by allocators, which are derived from the CBaseAllocator class. The CMediaSample constructor receives a pointer to an allocated buffer, along with the size of the buffer. Other properties are typically set and retrieved through IMediaSample interface methods.

The life cycle of a media sample differs from that of most COM objects:

  • The allocator holds a list of free samples. When a filter needs a new sample, it calls the allocator's IMemAllocator::GetBuffer method. The allocator retrieves a sample from its free list, increments the sample's reference count, and returns a pointer to the sample.
  • After the filter is done with the sample, it calls the IUnknown::Release method on the sample. Unlike most objects, the sample does not delete itself when its reference count reaches zero. Instead, it calls the IMemAllocator::ReleaseBuffer method on the allocator, and the allocator returns the sample to its free list.
  • The allocator does not destroy samples until the IMemAllocator::Decommit method is called.
Protected Member VariablesDescription
m_dwFlags Sample property flags.
m_dwTypeSpecificFlags Type-specific flags.
m_pBuffer Pointer to the memory buffer that contains the media data.
m_lActual Length of the valid data in the buffer, in bytes.
m_cbBuffer Size of the buffer, in bytes.
m_pAllocator Pointer to the allocator that created this sample.
m_pNext Pointer to the next sample in the allocator's list of samples.
m_Start Sample start time.
m_End Sample end time.
m_MediaStart Media start time.
m_MediaEnd Media stop time.
m_pMediaType Pointer to the media type, if the type has changed from the previous sample in the data stream.
m_dwStreamId Stream identifier.
Public Member Variables Description
m_cRef Reference count.
Public MethodsDescription
CMediaSample Constructor method.
~ CMediaSample Destructor method. Virtual.
SetPointer Sets the pointer to the memory buffer.
IMediaSample Methods Description
GetPointer Retrieves a read/write pointer to the buffer.
GetSize Retrieves the size of the buffer.
GetTime Retrieves the stream times at which this sample should begin and finish.
SetTime Sets the stream times at which this sample should start and finish.
IsSyncPoint Determines if the beginning of the sample is a synchronization point.
SetSyncPoint Specifies whether the beginning of this sample is a synchronization point.
IsPreroll Determines if this sample is a preroll sample.
SetPreroll Specifies whether this sample is a preroll sample.
GetActualDataLength Retrieves the length of the valid data in the buffer.
SetActualDataLength Sets the length of the valid data in the buffer.
GetMediaType Retrieves the media type, if the media type differs from the previous sample.
SetMediaType Sets the media type for the sample.
IsDiscontinuity Determines if this sample represents a break in the data stream.
SetDiscontinuity Specifies whether this sample represents a break in the data stream.
GetMediaTime Retrieves the media times for this sample.
SetMediaTime Sets the media times for this sample.
IMediaSample2 Methods Description
GetProperties Retrieves the properties of the sample.
SetProperties Sets the properties of the sample.

 

Requirements

Header

Amfilter.h (include Streams.h)

Library

Strmbase.lib (retail builds);
Strmbasd.lib (debug builds)

 

 

Community Additions

ADD
Show:
© 2015 Microsoft