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

README.hm12: documentation on the HM12 YUV format used by the cx23415/6 chip.
README.vbi: documentation on the V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI format
used in MPEG streams.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

2 files changed, 161 insertions, 0 deletions

diff --git a/Documentation/video4linux/cx2341x/README.hm12 b/Documentation/video4linux/cx2341x/README.hm12
new file mode 100644
index 0000000..0e213ed
--- /dev/null
+++ b/Documentation/video4linux/cx2341x/README.hm12
@@ -0,0 +1,116 @@
+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;
+}
+
+--------------------------------------------------------------------------
diff --git a/Documentation/video4linux/cx2341x/README.vbi b/Documentation/video4linux/cx2341x/README.vbi
new file mode 100644
index 0000000..5807cf1
--- /dev/null
+++ b/Documentation/video4linux/cx2341x/README.vbi
@@ -0,0 +1,45 @@
+
+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>