121 lines
4.0 KiB
Plaintext
121 lines
4.0 KiB
Plaintext
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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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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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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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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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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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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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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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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The width of a frame is always 720 pixels, regardless of the actual specified
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width.
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If the height is not a multiple of 32 lines, then the captured video is
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missing macroblocks at the end and is unusable. So the height must be a
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multiple of 32.
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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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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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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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// 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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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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// 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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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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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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if (argc == 1) fin = stdin;
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else fin = fopen(argv[1], "r");
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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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