diff --git a/Documentation/video4linux/cx2341x/README.hm12 b/Documentation/video4linux/cx2341x/README.hm12
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+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.
+
+--------------------------------------------------------------------------
+
+#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;
+}
+
+--------------------------------------------------------------------------