ICCompress function (vfw.h)

Article
10/05/2021

The ICCompress function compresses a single video image.

Syntax

DWORD VFWAPIV ICCompress(
  HIC                hic,
  DWORD              dwFlags,
  LPBITMAPINFOHEADER lpbiOutput,
  LPVOID             lpData,
  LPBITMAPINFOHEADER lpbiInput,
  LPVOID             lpBits,
  LPDWORD            lpckid,
  LPDWORD            lpdwFlags,
  LONG               lFrameNum,
  DWORD              dwFrameSize,
  DWORD              dwQuality,
  LPBITMAPINFOHEADER lpbiPrev,
  LPVOID             lpPrev
);

Parameters

hic

Handle to the compressor to use.

dwFlags

Compression flag. The following value is defined:

ICCOMPRESS_KEYFRAME

Compressor should make this frame a key frame.

lpbiOutput

Pointer to a BITMAPINFOHEADER structure containing the output format.

lpData

Pointer to an output buffer large enough to contain a compressed frame.

lpbiInput

Pointer to a BITMAPINFOHEADER structure containing the input format.

lpBits

Pointer to the input buffer.

lpckid

Reserved; do not use.

lpdwFlags

Pointer to the return flags used in the AVI index. The following value is defined:

AVIIF_KEYFRAME

Current frame is a key frame.

lFrameNum

Frame number.

dwFrameSize

Requested frame size, in bytes. Specify a nonzero value if the compressor supports a suggested frame size, as indicated by the presence of the VIDCF_CRUNCH flag returned by the ICGetInfo function. If this flag is not set or a data rate for the frame is not specified, specify zero for this parameter.

A compressor might have to sacrifice image quality or make some other trade-off to obtain the size goal specified in this parameter.

dwQuality

Requested quality value for the frame. Specify a nonzero value if the compressor supports a suggested quality value, as indicated by the presence of the VIDCF_QUALITY flag returned by ICGetInfo. Otherwise, specify zero for this parameter.

lpbiPrev

Pointer to a BITMAPINFOHEADER structure containing the format of the previous frame.

lpPrev

Pointer to the uncompressed image of the previous frame. This parameter is not used for fast temporal compression. Specify NULL for this parameter when compressing a key frame, if the compressor does not support temporal compression, or if the compressor does not require an external buffer to store the format and data of the previous image.

Return value

Returns ICERR_OK if successful or an error otherwise.

Remarks

You can obtain the required by size of the output buffer by sending the ICM_COMPRESS_GET_SIZE message (or by using the ICCompressGetSize macro).

The compressor sets the contents of lpdwFlags to AVIIF_KEYFRAME when it creates a key frame. If your application creates AVI files, it should save the information returned for lpckid and lpdwFlags in the file.

Compressors use lpbiPrev and lpPrev to perform temporal compression and require an external buffer to store the format and data of the previous frame. Specify NULL for lpbiPrev and lpPrev when compressing a key frame, when performing fast compression, or if the compressor has its own buffer to store the format and data of the previous image. Specify non-NULL values for these parameters if ICGetInfo returns the VIDCF_TEMPORAL flag, the compressor is performing normal compression, and the frame to compress is not a key frame.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	vfw.h
Library	Vfw32.lib
DLL	Msvfw32.dll

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