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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:05 EST.

1	The cx23416 can produce (and the cx23415 can also read) raw YUV output. The
2	format of a YUV frame is specific to this chip and is called HM12. 'HM' stands
3	for 'Hauppauge Macroblock', which is a misnomer as 'Conexant Macroblock' would
4	be more accurate.
5	
6	The format is YUV 4:2:0 which uses 1 Y byte per pixel and 1 U and V byte per
7	four pixels.
8	
9	The data is encoded as two macroblock planes, the first containing the Y
10	values, the second containing UV macroblocks.
11	
12	The Y plane is divided into blocks of 16x16 pixels from left to right
13	and from top to bottom. Each block is transmitted in turn, line-by-line.
14	
15	So the first 16 bytes are the first line of the top-left block, the
16	second 16 bytes are the second line of the top-left block, etc. After
17	transmitting this block the first line of the block on the right to the
18	first block is transmitted, etc.
19	
20	The UV plane is divided into blocks of 16x8 UV values going from left
21	to right, top to bottom. Each block is transmitted in turn, line-by-line.
22	
23	So the first 16 bytes are the first line of the top-left block and
24	contain 8 UV value pairs (16 bytes in total). The second 16 bytes are the
25	second line of 8 UV pairs of the top-left block, etc. After transmitting
26	this block the first line of the block on the right to the first block is
27	transmitted, etc.
28	
29	The code below is given as an example on how to convert HM12 to separate
30	Y, U and V planes. This code assumes frames of 720x576 (PAL) pixels.
31	
32	The width of a frame is always 720 pixels, regardless of the actual specified
33	width.
34	
35	If the height is not a multiple of 32 lines, then the captured video is
36	missing macroblocks at the end and is unusable. So the height must be a
37	multiple of 32.
38	
39	--------------------------------------------------------------------------
40	
41	#include <stdio.h>
42	#include <stdlib.h>
43	#include <string.h>
44	
45	static unsigned char frame[576*720*3/2];
46	static unsigned char framey[576*720];
47	static unsigned char frameu[576*720 / 4];
48	static unsigned char framev[576*720 / 4];
49	
50	static void de_macro_y(unsigned char* dst, unsigned char *src, int dstride, int w, int h)
51	{
52	    unsigned int y, x, i;
53	
54	    // descramble Y plane
55	    // dstride = 720 = w
56	    // The Y plane is divided into blocks of 16x16 pixels
57	    // Each block in transmitted in turn, line-by-line.
58	    for (y = 0; y < h; y += 16) {
59		for (x = 0; x < w; x += 16) {
60		    for (i = 0; i < 16; i++) {
61			memcpy(dst + x + (y + i) * dstride, src, 16);
62			src += 16;
63		    }
64		}
65	    }
66	}
67	
68	static void de_macro_uv(unsigned char *dstu, unsigned char *dstv, unsigned char *src, int dstride, int w, int h)
69	{
70	    unsigned int y, x, i;
71	
72	    // descramble U/V plane
73	    // dstride = 720 / 2 = w
74	    // The U/V values are interlaced (UVUV...).
75	    // Again, the UV plane is divided into blocks of 16x16 UV values.
76	    // Each block in transmitted in turn, line-by-line.
77	    for (y = 0; y < h; y += 16) {
78		for (x = 0; x < w; x += 8) {
79		    for (i = 0; i < 16; i++) {
80			int idx = x + (y + i) * dstride;
81	
82			dstu[idx+0] = src[0];  dstv[idx+0] = src[1];
83			dstu[idx+1] = src[2];  dstv[idx+1] = src[3];
84			dstu[idx+2] = src[4];  dstv[idx+2] = src[5];
85			dstu[idx+3] = src[6];  dstv[idx+3] = src[7];
86			dstu[idx+4] = src[8];  dstv[idx+4] = src[9];
87			dstu[idx+5] = src[10]; dstv[idx+5] = src[11];
88			dstu[idx+6] = src[12]; dstv[idx+6] = src[13];
89			dstu[idx+7] = src[14]; dstv[idx+7] = src[15];
90			src += 16;
91		    }
92		}
93	    }
94	}
95	
96	/*************************************************************************/
97	int main(int argc, char **argv)
98	{
99	    FILE *fin;
100	    int i;
101	
102	    if (argc == 1) fin = stdin;
103	    else fin = fopen(argv[1], "r");
104	
105	    if (fin == NULL) {
106		fprintf(stderr, "cannot open input\n");
107		exit(-1);
108	    }
109	    while (fread(frame, sizeof(frame), 1, fin) == 1) {
110		de_macro_y(framey, frame, 720, 720, 576);
111		de_macro_uv(frameu, framev, frame + 720 * 576, 720 / 2, 720 / 2, 576 / 2);
112		fwrite(framey, sizeof(framey), 1, stdout);
113		fwrite(framev, sizeof(framev), 1, stdout);
114		fwrite(frameu, sizeof(frameu), 1, stdout);
115	    }
116	    fclose(fin);
117	    return 0;
118	}
119	
120	--------------------------------------------------------------------------
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