Based on kernel version 4.7.2. Page generated on 2016-08-22 22:48 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 --------------------------------------------------------------------------