1The cx23416 can produce (and the cx23415 can also read) raw YUV output. The
2format of a YUV frame is specific to this chip and is called HM12. 'HM' stands
3for 'Hauppauge Macroblock', which is a misnomer as 'Conexant Macroblock' would
4be more accurate.
5
6The format is YUV 4:2:0 which uses 1 Y byte per pixel and 1 U and V byte per
7four pixels.
8
9The data is encoded as two macroblock planes, the first containing the Y
10values, the second containing UV macroblocks.
11
12The Y plane is divided into blocks of 16x16 pixels from left to right
13and from top to bottom. Each block is transmitted in turn, line-by-line.
14
15So the first 16 bytes are the first line of the top-left block, the
16second 16 bytes are the second line of the top-left block, etc. After
17transmitting this block the first line of the block on the right to the
18first block is transmitted, etc.
19
20The UV plane is divided into blocks of 16x8 UV values going from left
21to right, top to bottom. Each block is transmitted in turn, line-by-line.
22
23So the first 16 bytes are the first line of the top-left block and
24contain 8 UV value pairs (16 bytes in total). The second 16 bytes are the
25second line of 8 UV pairs of the top-left block, etc. After transmitting
26this block the first line of the block on the right to the first block is
27transmitted, etc.
28
29The code below is given as an example on how to convert HM12 to separate
30Y, U and V planes. This code assumes frames of 720x576 (PAL) pixels.
31
32The width of a frame is always 720 pixels, regardless of the actual specified
33width.
34
35If the height is not a multiple of 32 lines, then the captured video is
36missing macroblocks at the end and is unusable. So the height must be a
37multiple of 32.
38
39--------------------------------------------------------------------------
40
41#include <stdio.h>
42#include <stdlib.h>
43#include <string.h>
44
45static unsigned char frame[576*720*3/2];
46static unsigned char framey[576*720];
47static unsigned char frameu[576*720 / 4];
48static unsigned char framev[576*720 / 4];
49
50static 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
68static 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/*************************************************************************/
97int 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--------------------------------------------------------------------------
121