KS_VBI_FRAME_INFO structure (ksmedia.h)

The KS_VBI_FRAME_INFO structure extends the KSSTREAM_HEADER structure for vertical blanking interval (VBI) streams.

Syntax

typedef struct tagKS_VBI_FRAME_INFO {
  ULONG                  ExtendedHeaderSize;
  DWORD                  dwFrameFlags;
  LONGLONG               PictureNumber;
  LONGLONG               DropCount;
  DWORD                  dwSamplingFrequency;
  KS_TVTUNER_CHANGE_INFO TvTunerChangeInfo;
  KS_VBIINFOHEADER       VBIInfoHeader;
} KS_VBI_FRAME_INFO, *PKS_VBI_FRAME_INFO;

Members

ExtendedHeaderSize

Specifies the size of this structure.

dwFrameFlags

Specifies flags indicating additional information about the frame captured. During capture, the minidriver sets this member to one of the following values that are defined in ksmedia.h:

PictureNumber

Specifies a count representing the current picture number. Initialize or update this value on transition into KSSTATE_ACQUIRE.

DropCount

Specifies the number of pictures that were not captured. When capturing video, the minidriver sets this member. This counter should be incremented whenever a frame should have been captured but was not; this condition usually arises when no buffers were available during capture. Initialize or update this value on transition into KSSTATE_ACQUIRE.

dwSamplingFrequency

Specifies the sampling frequency in hertz (Hz).

TvTunerChangeInfo

Specifies information about the current VBI data source, including country/region code, analog video standard, and channel. This member is only valid if dwFrameFlags specifies the KS_VBI_FLAG_TVTUNER_CHANGE flag.

VBIInfoHeader

Specifies information about the current VBI data source, including start line, end line, sampling frequency, and video standard. This member is only valid if dwFrameFlags specifies the KS_VBI_FLAG_VBIINFOHEADER_CHANGE flag.

Remarks

The KS_VBI_FRAME_INFO structure provides a way to return information about a captured frame, as well as providing tuning information to VBI decoders.

The PictureNumber member count represents the count of the current picture based on the format used to open the stream. This count is calculated in one of two ways, depending on the device:

1. Measure the time since the stream was started and divide by the frame duration. This method is appropriate for devices that do not provide their own clock. For example: PictureNumber = (CurrentStreamTime − StartStreamTime) / FrameDuration

2. Add together the count of frames captured and the count of frames dropped. This method is appropriate for devices that provide their own clock. For example: PictureNumber = FramesCaptured + FramesDropped

When calculating the PictureNumber and DropCount, it is important to use the frame duration specified when the stream was opened, which may not necessarily match the rate at which the device is actually producing images. For example, a USB camera may only produce images at 7.5 fps, but a client could open the stream at 8 fps. In this case, all calculations should use the 8 fps number. For more information about updating PictureNumber and DropCount see Capturing Video.

The dwSamplingFrequency member is not used by Microsoft VBI codecs, but may be used by other WDM codecs. It must be the same as the VBIInfoHeader.SamplingFrequency member. A minidriver indicates a change in sampling frequency by setting the KS_VBI_FLAG_VBIINFOHEADER_CHANGE bit in the dwFrameFlags member, and filling in all members, including dwSamplingFrequency, in the VBIInfoHeader structure.

Requirements

See also

KSSTREAM_HEADER

KS_TVTUNER_CHANGE_INFO

KS_VBIINFOHEADER