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