videocapture::set not working (Bug #4270)

GuoDong Goh wrote:

Hi all,

I am having difficulty setting the frame size. I have tried using
capture.set(CV_CAP_PROP_FRAME_WIDTH,1280);
capture.set(CV_CAP_PROP_FRAME_HEIGHT,720);
but it just doesn't change accordingly.

I have seen thread related to this (Bug #948) and i did exactly the same thing as Alexander Shishkov recommended but to no avail.

Can anyone help? Thanks

I have the same issue here with Win 8.1 x64 and a Microsoft LifeCam (USB UVC device) and the latest OpenCV from master branch.

The capture.set values provided will be cached internally and finally VD->streamConf->SetFormat is called in file cap_dshow.cpp which returns E_FAIL. After finding and reading https://github.com/ofTheo/videoInput/issues/6 I added a few lines to correct lSampleSize in setSizeAndSubtype:

 1    if (mediatype == MEDIASUBTYPE_RGB24)
 2    {
 3        VD->pAmMediaType->lSampleSize = attemptWidth*attemptHeight*3;
 4    }
 5    else if (mediatype == MEDIASUBTYPE_YUY2)
 6    {
 7        VD->pAmMediaType->lSampleSize = attemptWidth*attemptHeight * 2;
 8    }
 9    else

Note that this is a workaround just for one mediatype. At least, YUY2 is the packed 4:2:2 YUV format recommended in the USB UVC Spec, so this fix should help for many USB cams. There are more mediatypes (e.g. various YUV formats) to fix. I suggest to calculate lSampleSize from pVih->bmiHeader where biBitcount says 16 in my case. But, this probably needs lots of regression testing.

hth

Frank