Working with MFT Media Buffers and Samples

Codec MFTs pass media data back and forth by using media buffers and samples.

A media buffer is a COM object that manages a block of memory, typically to hold media data. When data is passed to or from an MFT, it is always passed in the form of a media buffer.

All media buffers expose the IMFMediaBuffer interface. This interface is designed for any type of data. Buffers containing video data often also expose IMF2DBuffer.

A media buffer has a maximum size, which is the amount of memory allocated for the buffer. To find the maximum size, call IMFMediaBuffer::GetMaxLength. At any point in time, a media buffer also has a current length, which is the amount of valid data in the buffer, ranging from zero bytes up to the maximum size. To get the current length, call IMFMediaBuffer::GetCurrentLength. When the buffer is created, the current length is zero. If you write data to the buffer, call IMFMediaBuffer::SetCurrentLength to update the current length.

To access the memory in the buffer, call IMFMediaBuffer::Lock. This method returns a pointer to the start of the memory block. When you are done using the pointer, call IMFMediaBuffer::Unlock. The Lock method is not a thread synchronization mechanism; it does not guarantee that other threads cannot access the buffer. The Lock method is used to assure that the memory accessed will remain valid until you call the Unlock method.

A media sample object (in the context of the Media Foundation SDK) is an object that contains an ordered list of zero or more buffers. Media samples expose the IMFSample interface.

To create a new sample, call the MFCreateSample function. Initially, the sample's buffer list is empty. To add a buffer to the end of the list, call IMFSample::AddBuffer.

Related topics

Working with Codec DMOs
Working with Codec MFTs

 

 

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