Important notes

Negotiating Pin Connections:
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When the Filter Graph Manager tries to connect two filters, the pins must agree on various things. If they cannot, the connection attempt fails. Generally, pins negotiate the following:
1.Transport
2.Media type
3.Allocator
Transport:
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The transport is the mechanism that the filters will use to move media samples from the output pin to the input pin. For example, they can use the IMemInputPin interface ("push model") or the IAsyncReader interface ("pull model").

Media type:
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Almost all pins use media types to describe the format of the data they will deliver.
Allocator:
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The allocator is the object that creates the buffers that hold the data. The pins must agree which pin will provide the allocator. They must also agree on the size of the buffers, the number of buffers to create, and other buffer properties.
The base classes implement a framework for these negotiations. You must complete the details by overriding various methods in the base class. The set of methods that you must override depends on the class and on the functionality of your filter.

Processing and Delivering Data:
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The primary function of most filters is to process and deliver media data. How that occurs depends on the type of filter:
A push source has a worker thread that continuously fills samples with data and delivers them downstream.

A pull source waits for its downstream neighbor to request a sample. It responds by writing data into a sample and delivering the sample to the downstream filter. The downstream filter creates the thread that drives the data flow.
A transform filter has samples delivered to it by its upstream neighbor. When it receives a sample, it processes the data and delivers it downstream.
A renderer filter receives samples from upstream, and schedules them for rendering based on the time stamps.