10. Small Filter Guide
Even under perfect reception conditions the DVBViewer may not show the desired results. This is mostly due to the fact that important components for audio and video playback are missing. Also other programs can interfere with the DVBViewer because they altered some registry-settings or installed certain DirectShow-components with a higher merit (a description follows down below). You should study this chapter quite thoroughly in case of having problems. But you might consider the information provided useful, if you're just interested.
What Are DirectShow Filters?
With DirectShow (part of DirectX) Microsoft introduced a very flexible multimedia interface, which is used by almost every modern media player under windows. DirectShow components are often named as filters (although it doesn't apply in each case) and are registered in the system and are so accessible by other programs. In most cases their file-type is .ax, but sometimes also .dll.
Processing audio and video data streams a long chain of such filters can be involved - each one is responsible for a certain function. The DVBViewer and media-players in general only manage those filters or decoders. They are only indirectly concerned with the processing of the data streams.
A compilation of the necessary filters is sent to the DirectShow filter-manager. If you want to play a video-file for example the manager is told to trace the necessary filters for creating the filter graph. Sometimes the automatic building process leads to unwanted results; therefore certain DirectShow based programs can manually adjust the building process, for example determining the use of a certain filter. Usually the manager uses the “best” filter available. “Best” is not to be understood as quality. “Best” is determined by the merit value of a filter. The filter with the highest merit will always be used. The merit value is set by the filter's author. Therefore the results may not be optimal. Fortunately you can modify the merit value.
Which Filters Are Involved?
The first or “main” filter is the source-filter, which provides the data stream received via satellite (consisting of audio, video and if necessary also teletext and EPG).
The DVBViewer features a proprietary source-filter:
DVBViewer filter (DVBSource): This filter sports an integrated demultiplexer and is used for both live-tv and media playback, there are none of the weaknesses of the Microsoft demultiplexer. A demultiplexer separates the audio and video streams and is responsible for fast seeking in a file, in short it is a parser. .It can also be used for playback of separate .mp2 and .ac3 files.
The next filters in the chain are responsible for decompressing the audio and video data. These filters are the decoders. The decoding is the most difficult and time-consuming step in the whole process. The playback quality depends highly on the decoders.
With the installation of the TechniSat software a suitable video decoder, the Mediamatics/DVDExpress decoder (until driver release 4.2.10) or the Sonic decoder (since driver release 4.3.0) , is installed automatically. In case of problems with audio playback you should install the free Moonlight/Elecard Odio Dekoda.
Reminder: The selected filters have to be installed since the DVBViewer does not bring its own filters.
The end of the chain are the audio- and video-renderers, which send the data via drivers to the graphic- and sound-card. The video renderer can be chosen at Options/Enhanced/Render Output. You'll find a description in this paragraph in chapter 7. You can also set different audio-renderers, but those are only different interfaces to the sound-card (see Settings/Options/DirectShow/Dedynamic Filter).