Scanning to Tunable Signals
This section applies only to operating systems starting with Microsoft Windows Vista.
Signal scanning is the process of locking to the next tunable signal (up or down) that is broadcast along a range of frequency values on a cable or antenna system. For operating systems earlier than Windows Vista, signal scanning is driven largely by software (the KsTvTune.ax module) and is based on scanning a known map of channels as opposed to a frequency-based scan of the broadcast spectrum. If an AVStream minidriver that runs on Windows Vista reports back signal-scanning capabilities through a new-for-Windows Vista property in the PROPSETID_TUNER property set, the tuner filter (KsTvTune.ax) and the applications above can use those capabilities for scanning. If the driver does not support the new frequency-based scanning functionality, KsTvTune.ax falls back to the former channel-based scanning functionality.
The tuner filter and an AVStream minidriver can handle the new frequency-based scanning functionality by using a hardware-assisted scanning algorithm.
When scanning completes, the minidriver must signal an event handle. For information about the event operation flow, see Event Mechanism and Flow.
To support the new frequency-based scanning functionality, the minidriver must implement the required property in the following list and optionally implement the remaining properties and the event: