Broadcast-driven system (TTS) series of lectures: 2

Ii. Unified Microsoft tuning model
To adapt to different network types, Microsoft has defined a unified tuning model ). This model makes the applicationProgramIt can be tuned to any application of any network type that uses any compatible device using a standard process.

1. tuning process overview
The basic method for application tuning and program selection is to submit a tuning request to the network provider filter. As mentioned above, the network provider filter will be associated with the device filter (driver) After receiving the tuning request) communication and hardware tuning. The method recommended by Microsoft to retrieve a tuning request is to retrieve a tuning request from the created guide store, this type of wizard library contains Program-related information that can be displayed to end users and network-specific information for hardware tuning. Generally, this wizard library appears in the following location of the registry: HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Tuning
Spaces.
[Img] http://www.cctvpro.com.cn/jxlt/20010817/200108172910.gif#/img]
Figure 2 shows the relationship between the tuning model objects. As shown in 2, the system tuning space object contains a set of tuning spaces, each of which represents a different network type (ATSC, DVB-C, DVB-S and DVB-T, etc.), the tuning space contains information about tuning to a specific program, the tuning request object is based on it. The locator object contains other information about the signal source. A tuning space can contain a default locator to locate the default stream in the multiplexing transmission stream. Obviously, the tuning space object, the tuning request object and the positioner object are all related to the specific network type, so the specific objects are also different.

A specific program can contain one or more basic streams. Each basic stream is called a component and described by the component type (component types, such as audio or video components. Some components can be manually excluded. For example, if the same program may contain two audio streams in different languages, you can select one and remove the other. A tuning space can contain a preferred Component Types list to select the default component from the stream, applications can overwrite this default option based on user requirements and select other components.

2. Operation Sequence of the tuning process
Information related to the tuning is always contained in the tuning request object, and the application sends the tuning request to the network provider filter for tuning. Tuning is divided into two phases: locating and obtaining.

(1) signal Positioning
The network provider filter first passes the tuning request information to the transport MPEG-2 transport information filter (TIF) filter in the filter chart, where TIF fills in the information required by the tuner for signal locating, for example, the carrier frequency (Carrier Frequency. A tuning request may contain a locator associated with it. If not, Tif will create a default locator for it.
The network provider filter then requires the tuning tuner to tune to the correct frequency and set the parameter information required by the tuner, such as the forward correction (FEC) rate. After the tuner receives the signal, it forwards it to the capture filter of the receiver ), the capture filter digitizes the signal and sends the digital MPEG-2 transmission stream to the MPEG-2 demultiplexer de-multiplexing filter.
The TIF filter always maps a stream whose PID is 0 to itself. This PID is reserved for the program Association Table pat. When TIF receives Pat, it notifies the network provider that the program ing table (Program Map Table) PMT table and other tables are on those PIDs.

(2) Signal Acquisition
The network provider filter obtains a program component list by asking TIF. It can activate or shield some components based on the prioritized component list, and then map the corresponding PID to the demultiplexing filter, which is responsible for sending the corresponding stream to the corresponding PIN. For a PID stream not mapped to any output pin, the demultiplexing filter will discard it. TIF constantly monitors the PMT while the filter chart is running to discover service changes, and notifies the network provider of the changes in a timely manner.

3. tuning-related objects
(1) tuning Space
A tuning space represents a specific network type and mainly implements the following functions:

* Save information about the network;
* Is the manufacturing factory of the tuning request object;
* Is permanent. Can be saved in the registry.
To obtain all available tuning spaces of the local system, the unified tuning model provides the systemtuningspaces object and exposes the ituningspacescontainer interface on this object for convenient tuning space enumeration. Each tuning space object exposes an interface inherited from ituningspace. The application uses the createtunerequest method of this interface to generate a tuning request object. Of course, the unified tuning model also allows the application to generate a new tuning space and set the default positioner.

(2) tuning requests, locators and basic flow components
For Digital TVs, both initial signal locating and subsequent discovery of audio and video and basic data streams require tuning. Therefore, for the entire tuning operation, the tuning request object is placed in a central position because it contains (or provides obtaining means) The information required for tuning.

The only method generated by the tuning request object is to call the createtunerequest method of the tuning space. As mentioned above, the tuning request contains Network-related information, locator information, and default component information.

The positioner object is also related to a specific network, for example, the locator referenced by the DVB-S is the DVB-S locator. The positioner contains the further information required for the network provider filter to locate a specific service, such as the carrier frequency, symbol rate, polarization direction, and power supply.

The unified tuning model also provides the icomponent interface for selecting basic stream components. If you do not select, the network provider filter configures the output pin of the MPEG-2 demultiplexer Filter Using the preference component list. The default pin configuration is as follows:

* Pin1: PSI (Program Specific information) table information. Send to Tif filter;
* Pin2: video stream;
* Pin3: audio stream;
* Pin4: data stream;
* Pin5: PSI table information. To the MPEG-2 section and tables filter.

4. Acquisition of Program-related information
To obtain Program-related information from a transmission stream, such as Pat, PMT, and CAT. There are mainly the following methods:
* Obtained from the TIF filter;
* Obtained from the MPEG-2 section and tables filter;
* Implement a user-level filter to parse the original PSI package;
The above filters provide corresponding interfaces to obtain program information, and can be used in combination with the above methods.