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The Filter
Graph Manager
is a COM object that controls the filters in a filter graph.
It performs many functions, including the following:
Coordinating state changes among the filters.
Establishing a reference
clock
.
Communicating events back to the application.
Providing methods for applications to build the filter graph.
Filter Graph Manager
是一个
COM
对象，是
filter graph
中控制
filters
的对象。它执行许多功能，包括：
调整一类
filters
的状态变化。
建立一个引用时钟。
返回事件给应用程序。
提供方法给应用程序生成
filter graph
。
Each of these functions is described briefly here. Details can be
found elsewhere in the documentation.
State changes.
State changes within filters must occur in a particular order.
Therefore, the application does not issue state-change commands directly to the
filters. Instead, it gives a single command to the Filter Graph Manager, which
distributes the command to each of the filters. Seeking works in a similar
fashion: The application gives a seek command to the Filter Graph Manager,
which distributes it to the filters.
Reference clock.
All of the filters in the graph use the same clock, called a
reference clock. The reference clock ensures that all the streams are
synchronized. The time at which a video frame or audio sample should be
rendered is called the presentation time. The presentation time is measured
relative to the reference clock. The Filter Graph Manager chooses a reference
clock, usually either the clock on the sound card, or the system clock.
Graph events.
The Filter Graph Manager uses an event queue to inform the
application of events that occur in the filter graph. This mechanism is similar
to a Windows message loop.
Graph-building methods.
The Filter Graph Manager provides methods for the application to add
filters to the graph, connect filters to other filters, and disconnect filters.
State
changes.
filters
内的状态变化必须发生在特殊的命令中。因此，应用程序不直接像
filters
发送状态转化命令。而是给
Filter Graph Manager
一个单独的命令，由
Filter Graph Manager
给每一个
filters
分发命令。
Reference
clock.
graph
中的所有
filter
都使用相同的时钟，这个时钟叫做
reference clock. referrence
确保所有的流同步。
The time at which a video frame or audio sample
should be rendered is called the presentation time. The presentation time is
measured relative to the reference clock. Filter Graph Manager
选择声卡时钟或者系统时钟作为
reference clock
。
Graph
events.
Filter Graph Manager
使用事件队列通知接收
filter graph
中产生消息的应用程序。这个机制类似
Windows
的消息循环。
Graph-building
methods.
Filter Graph Manager
为应用程序提供了添加
filter
到
graph
，连接两个
filter
，断开
filter
连接的方法。
One function the Filter Graph Manager does not handle is moving data
from one filter to the next. This is done by the filters themselves, through
their pin connections. Processing always happens on a separate thread.
有一个功能是
Filter Graph Manage
没有处理的，那就是把数据从一个
filter
移动到下一个。这是由
filter
通过
pin
的连接来完成。处理过程总是发生在一个分离线程。