If you are developing a TV tuner application for your tuner device using Direct Show, then you will definitely look for some function which can perform fine TV tuning (i.e., you want to set video frequency manually to get the precise video signal on a specific TV channel), but unfortunately, there in no such function in standard DirectShow TV tuning interfaces
The DirectShow TV tuning architecture is based on pre-defined frequency tables, and the TV Tuner filter (kstvtune.ax) has an internal list of frequency tables. Each frequency table contains a list of frequencies, and corresponds to the broadcast or cable frequencies for a given country/region. So, when you use the
IAMTuner interface, it gets the channel frequency values from the internal frequency tables according to the selected country/ region and tunes the TV channels.
IAMTuner interface will not allow you to modify the frequency values for a specific channel manually, you can't fine tune a channel while previewing. However, there is an
AutoTune function available in
IAMTVTuner interface which can help you to fine tune a channel, but this will also give you no control for manual fine tuning on the fly or to set custom video frequencies.
But the following code will describe you the complete details of fine tuning on the fly using
IKsPropertySet. I am writing this article only to help those who really want to get some clue on fine TV tuning because I know how difficult it is to get help on this topic. Even, you will not find a single function in the whole DirectShow documentation which can help you on this.
While writing this code, I assumed that the reader has good knowledge of DirectShow video capturing and know the details of DirectShow graph building techniques, filers, and TV tuner graphs. I hope the DirectShow guys will be happy after reading this article.
This is my first article on Code Project, so some of you may find it difficult to read .
#define INSTANCEDATA_OF_PROPERTY_PTR(x) ((PKSPROPERTY((x))) + 1)
#define INSTANCEDATA_OF_PROPERTY_SIZE(x) (sizeof((x)) - sizeof(KSPROPERTY))
HRESULT SetFrequency(long Freq)
hr = m_pTvtuner->QueryInterface(IID_IKsPropertySet, (void**)&m_pKSProp);
ModeCaps.Mode = AMTUNER_MODE_TV;
hr = m_pKSProp->QuerySupported(PROPSETID_TUNER,
if(SUCCEEDED(hr) && dwSupported&KSPROPERTY_SUPPORT_GET)
hr = m_pKSProp->Get(PROPSETID_TUNER,KSPROPERTY_TUNER_MODE_CAPS,
if(Freq>=ModeCaps.MinFrequency && Freq<=ModeCaps.MaxFrequency)
hr = m_pKSProp->Set(PROPSETID_TUNER,
Explanation of Code
SetFrequency functions set the video frequency of a tuner device, the only parameter
Freq is the desired video frequency in Hz. The code is using
IKsPropertySet interface to perform the desired operations,
IKsPropertySet interface is part of the WDM KS (Win32® Driver Model Kernel Streaming) architecture and allows drivers to provide extended capabilities that can be used without API extensions.
The basic 3 steps performed by this code are..
- Check the support of
IKsPropertySet on Tuner Drivers.
- Check the
PROPSETID_TUNER property on Tuner Drivers.
- Set the user defined video frequency on tuner in Hz.
Using the Code
SetFrequency function can be used in several ways, i.e., fine TV tuning, manual TV tuning, new TV channels tuning, and etc.
- Fine tuning of a tuned TV channel.
IAMTuner::put_Channel to set the desired TV channel.
IAMTVTuner::get_VideoFrequency to get the current video frequency.
SetFrequency by adding the desired +/- frequency value in the original channel frequency and perform the operation until you find the best video quality on that channel.
- Manual TV tuning.