V4L/DVB (4547): Add YUV HM12 and VBI IVTV format documentation.

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;

}

--------------------------------------------------------------------------

Format of embedded V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data

=========================================================

This document describes the V4L2_MPEG_STREAM_VBI_FMT_IVTV format of the VBI data

embedded in an MPEG-2 program stream. This format is in part dictated by some

hardware limitations of the ivtv driver (the driver for the Conexant cx23415/6

chips), in particular a maximum size for the VBI data. Anything longer is cut

off when the MPEG stream is played back through the cx23415.

The advantage of this format is it is very compact and that all VBI data for

all lines can be stored while still fitting within the maximum allowed size.

The stream ID of the VBI data is 0xBD. The maximum size of the embedded data is

4 + 43 * 36, which is 4 bytes for a header and 2 * 18 VBI lines with a 1 byte

header and a 42 bytes payload each. Anything beyond this limit is cut off by

the cx23415/6 firmware. Besides the data for the VBI lines we also need 36 bits

for a bitmask determining which lines are captured and 4 bytes for a magic cookie,

signifying that this data package contains V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data.

If all lines are used, then there is no longer room for the bitmask. To solve this

two different magic numbers were introduced:

'itv0': After this magic number two unsigned longs follow. Bits 0-17 of the first

unsigned long denote which lines of the first field are captured. Bits 18-31 of

the first unsigned long and bits 0-3 of the second unsigned long are used for the

second field.

'ITV0': This magic number assumes all VBI lines are captured, i.e. it implicitly

implies that the bitmasks are 0xffffffff and 0xf.

After these magic cookies (and the 8 byte bitmask in case of cookie 'itv0') the

captured VBI lines start:

For each line the least significant 4 bits of the first byte contain the data type.

Possible values are shown in the table below. The payload is in the following 42

bytes.

Here is the list of possible data types:

#define IVTV_SLICED_TYPE_TELETEXT       0x1     // Teletext (uses lines 6-22 for PAL)

#define IVTV_SLICED_TYPE_CC             0x4     // Closed Captions (line 21 NTSC)

#define IVTV_SLICED_TYPE_WSS            0x5     // Wide Screen Signal (line 23 PAL)

#define IVTV_SLICED_TYPE_VPS            0x7     // Video Programming System (PAL) (line 16)

Hans Verkuil <hverkuil@xs4all.nl>