On Sun, 6 Mar 2011, Andy Walls wrote: > On Sat, 2011-03-05 at 22:49 -0600, Aguirre, Sergio wrote: > > Hi, > > > > I was curious in how to handle properly buffers of pixelformat V4L2_PIX_FMT_NV12. > > > > I see that the standard convention for determining a bytesize of an image buffer is: > > > > bytesperline * height > > > > However, for NV12 case, the bytes per line is equal to the width, _but_ the actual buffer size is: > > > > For the Y buffer: width * height > > For the UV buffer: width * (height / 2) > > Total size = width * (height + height / 2) > > > > Which I think renders the bytesperline * height formula not valid for this case. > > > > Any ideas how this should be properly handled? > > For the HM12 macroblock format: > > http://git.linuxtv.org/media_tree.git?a=blob;f=Documentation/video4linux/cx2341x/README.hm12;h=b36148ea07501bdac37ae74b31cc258150f75a81;hb=staging/for_v2.6.39 > > ivtv and cx18 do this in cx18-ioctl.c and ivtv-ioctl.c: > > ... > if (id->type == xxxx_ENC_STREAM_TYPE_YUV) { > pixfmt->pixelformat = V4L2_PIX_FMT_HM12; > /* YUV size is (Y=(h*720) + UV=(h*(720/2))) */ > pixfmt->sizeimage = pixfmt->height * 720 * 3 / 2; > pixfmt->bytesperline = 720; > } > ... Yep, the height * width formula is in no way "standard" or "compulsory" - that's exactly the reason why this calculation is left to the individual drivers. You can also look at sh_mobile_ceu_camera.c, which also supports this format, and effectively also calculates height * width * 3 / 2. Thanks Guennadi > > Note that the wdith is fixed at 720 because the CX2341x chips always > build HM12 planes assuming a width of 720, even though it isn't going to > actually fill in the off-sceen pixels for widths less than 720. > > > Note that "pixfmt->height * 3 / 2" is just "(height + height / 2)". > > It's not a definitive answer; only an example of what two drivers do for > a very uncommon macroblock format. > > Regards, > Andy > > > NOTE: See here for more details: http://www.fourcc.org/yuv.php#NV12 > > > > Regards, > > Sergio-- > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
