AVIStreamRead return data wrong

Hello,

I am using AVIStreamRead to read AVI video,
AVIStreamRead(gapavi[0], i, 1, frame, bsize, &nBytes, &nSamples)

but the data returned in frame is shifted 3 DWORDs. for example
the data returned in frame is:
00 00 00 00 30 30 64 63 00 60 09 00 86 79 87 80 ...

where 86 is the first pixel of the video. and I think 30 30 64 63 (00dc)
means video chunk
and 00 60 09 00 is the picture size (buffer size, 640x480, yuy2) first four
00 are last JUNK chunk data (note: the first chunk in movi LIST is a JUNK
chunk)

So anyone know why AVIStreamRead read the data wrong? really appreciate your
help.
thanks in advance.