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; } ... 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
