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Diffstat (limited to 'kernel/Documentation/video4linux/cx2341x/README.hm12')
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diff --git a/kernel/Documentation/video4linux/cx2341x/README.hm12 b/kernel/Documentation/video4linux/cx2341x/README.hm12 new file mode 100644 index 000000000..b36148ea0 --- /dev/null +++ b/kernel/Documentation/video4linux/cx2341x/README.hm12 @@ -0,0 +1,120 @@ +The cx23416 can produce (and the cx23415 can also read) raw YUV output. The +format of a YUV frame is specific to this chip and is called HM12. 'HM' stands +for 'Hauppauge Macroblock', which is a misnomer as 'Conexant Macroblock' would +be more accurate. + +The format is YUV 4:2:0 which uses 1 Y byte per pixel and 1 U and V byte per +four pixels. + +The data is encoded as two macroblock planes, the first containing the Y +values, the second containing UV macroblocks. + +The Y plane is divided into blocks of 16x16 pixels from left to right +and from top to bottom. Each block is transmitted in turn, line-by-line. + +So the first 16 bytes are the first line of the top-left block, the +second 16 bytes are the second line of the top-left block, etc. After +transmitting this block the first line of the block on the right to the +first block is transmitted, etc. + +The UV plane is divided into blocks of 16x8 UV values going from left +to right, top to bottom. Each block is transmitted in turn, line-by-line. + +So the first 16 bytes are the first line of the top-left block and +contain 8 UV value pairs (16 bytes in total). The second 16 bytes are the +second line of 8 UV pairs of the top-left block, etc. After transmitting +this block the first line of the block on the right to the first block is +transmitted, etc. + +The code below is given as an example on how to convert HM12 to separate +Y, U and V planes. This code assumes frames of 720x576 (PAL) pixels. + +The width of a frame is always 720 pixels, regardless of the actual specified +width. + +If the height is not a multiple of 32 lines, then the captured video is +missing macroblocks at the end and is unusable. So the height must be a +multiple of 32. + +-------------------------------------------------------------------------- + +#include <stdio.h> +#include <stdlib.h> +#include <string.h> + +static unsigned char frame[576*720*3/2]; +static unsigned char framey[576*720]; +static unsigned char frameu[576*720 / 4]; +static unsigned char framev[576*720 / 4]; + +static void de_macro_y(unsigned char* dst, unsigned char *src, int dstride, int w, int h) +{ + unsigned int y, x, i; + + // descramble Y plane + // dstride = 720 = w + // The Y plane is divided into blocks of 16x16 pixels + // Each block in transmitted in turn, line-by-line. + for (y = 0; y < h; y += 16) { + for (x = 0; x < w; x += 16) { + for (i = 0; i < 16; i++) { + memcpy(dst + x + (y + i) * dstride, src, 16); + src += 16; + } + } + } +} + +static void de_macro_uv(unsigned char *dstu, unsigned char *dstv, unsigned char *src, int dstride, int w, int h) +{ + unsigned int y, x, i; + + // descramble U/V plane + // dstride = 720 / 2 = w + // The U/V values are interlaced (UVUV...). + // Again, the UV plane is divided into blocks of 16x16 UV values. + // Each block in transmitted in turn, line-by-line. + for (y = 0; y < h; y += 16) { + for (x = 0; x < w; x += 8) { + for (i = 0; i < 16; i++) { + int idx = x + (y + i) * dstride; + + dstu[idx+0] = src[0]; dstv[idx+0] = src[1]; + dstu[idx+1] = src[2]; dstv[idx+1] = src[3]; + dstu[idx+2] = src[4]; dstv[idx+2] = src[5]; + dstu[idx+3] = src[6]; dstv[idx+3] = src[7]; + dstu[idx+4] = src[8]; dstv[idx+4] = src[9]; + dstu[idx+5] = src[10]; dstv[idx+5] = src[11]; + dstu[idx+6] = src[12]; dstv[idx+6] = src[13]; + dstu[idx+7] = src[14]; dstv[idx+7] = src[15]; + src += 16; + } + } + } +} + +/*************************************************************************/ +int main(int argc, char **argv) +{ + FILE *fin; + int i; + + if (argc == 1) fin = stdin; + else fin = fopen(argv[1], "r"); + + if (fin == NULL) { + fprintf(stderr, "cannot open input\n"); + exit(-1); + } + while (fread(frame, sizeof(frame), 1, fin) == 1) { + de_macro_y(framey, frame, 720, 720, 576); + de_macro_uv(frameu, framev, frame + 720 * 576, 720 / 2, 720 / 2, 576 / 2); + fwrite(framey, sizeof(framey), 1, stdout); + fwrite(framev, sizeof(framev), 1, stdout); + fwrite(frameu, sizeof(frameu), 1, stdout); + } + fclose(fin); + return 0; +} + +-------------------------------------------------------------------------- |