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Introduction
As well known, AVICap window class provides applications with
a message-based interface to access video and waveform-audio
acquisition hardware and to control the process of streaming
video capture to disk. Unfortunately, it has a few serious
limitations:
- All of setup operations for format, source and
videostandard are implemented within driver dialogs.
Program control is
complicated and without of any warranties of true
results. - Capture conditions are strongly related with WM_VISIBLE
flag of AVICap window. - There is no ability of window stretching.
- Most of capture drivers has internal buffers queue
(fifo), so they can’t provide satisfactory time accuracy
when user application needs to grab a single frame. They
simply returns last frame from buffers queue.
In short, AVICap window is really good enough for control the
process of streaming video capture to disk,
but in most cases useless for real-time video processing.
For resolving this problem, i have wrote my own wrapper for
AVICap windows which extended its functionality in order to work
with real-time videoprocessing application.
Note: Win16 API provides
interface for direct drivers access (all capture drivers, i know
are 16 bits). This allows to build real-time program without huge
and slow AVICap windows. Win32 API do not allow to interface with
16 bits drivers directly.
Class Implementation
Class AviCap was implemented by usual for MFC
way("dynamically subclass"). Most of public methods are
helpers for WM_CAP_XXXX messaging, but a few methods gives
enhanced control for programmers.
Connection:
//Connect with specific driver. According to compile setting and //m_DoQuickConnection flag, connection can be quick or with a full //preliminary testing BOOL ConnectWithDriver(LPCSTR Name=NULL); BOOL ConnectWithDriver(INT indx);
Enhanced control:
//Reset internal driver buffers queue(if exist) VOID ResetCache(); //Quick format setup BOOL SetFormat(LPBITMAPINFO bmpinf); BOOL SetBitResolution(UINT reqBitsCount); BOOL SetFrameSize(INT x, INT y); BOOL SetFrameSize(CSize sz);
Enhanced formats information:
//Fill struct with a driver infoBOOL GetDriverInfo(CAPDRVINFO *cdi); //Quick information about current format CSize GetFrameSize(); DWORD GetRequiredBufferSize(); LPBITMAPINFO GetCurrentFormat(); BOOL IsSupportedBitsResolution(UINT uBitsCount); DWORD GetCurrentBitsResolution(); //Enumerate all valid frame sizes BOOL EnumValidFrameSize(CSize &sz, int indx);
Driver information:
//Get full list of installed capture drivers INT GetDriversList(CStringArray *Names, CStringArray *Versions); //Get current driver name, version and index LPCSTR GetDriverName(); LPCSTR GetDriverVer(); INT GetDriverIndex();
Setup specific callbacks functions for painting and progress notification:
//Setup callback for painting on the capture window
VOID SetDrawCallBack(DRAWCALLBACK cb);
/Setup callback for notification about progress during testing
VOID SetProgressCallback(LPVOID cb);
Other:
//Switch Stretch/No mode
VOID AdjustPlacement(BOOL fStretch=FALSE);
Notes:
- Some drivers can splash Message box during testing.
- The list of "public formats" from driver dialog
can be appreciable different from list that you can get
using EnumValidFrameSize method. This is a really strange
fact, but it can be very useful.
Demo program:
Project was compiled and tested
with MSV C++ 5.0. This small demo program connect with first
capture driver installed on computer and performs full testing of
driver. Some of "standard" and "enhanced"
commands of this class are gathered in menu.
