178 lines
6.2 KiB
ReStructuredText
178 lines
6.2 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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The cx2341x driver
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==================
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Non-compressed file format
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--------------------------
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The cx23416 can produce (and the cx23415 can also read) raw YUV output. The
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format of a YUV frame is 16x16 linear tiled NV12 (V4L2_PIX_FMT_NV12_16L16).
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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 V4L2_PIX_FMT_NV12_16L16
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to separate 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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Raw format c example
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~~~~~~~~~~~~~~~~~~~~
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.. code-block:: c
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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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Format of embedded V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data
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---------------------------------------------------------
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Author: Hans Verkuil <hverkuil@xs4all.nl>
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This section describes the V4L2_MPEG_STREAM_VBI_FMT_IVTV format of the VBI data
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embedded in an MPEG-2 program stream. This format is in part dictated by some
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hardware limitations of the ivtv driver (the driver for the Conexant cx23415/6
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chips), in particular a maximum size for the VBI data. Anything longer is cut
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off when the MPEG stream is played back through the cx23415.
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The advantage of this format is it is very compact and that all VBI data for
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all lines can be stored while still fitting within the maximum allowed size.
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The stream ID of the VBI data is 0xBD. The maximum size of the embedded data is
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4 + 43 * 36, which is 4 bytes for a header and 2 * 18 VBI lines with a 1 byte
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header and a 42 bytes payload each. Anything beyond this limit is cut off by
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the cx23415/6 firmware. Besides the data for the VBI lines we also need 36 bits
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for a bitmask determining which lines are captured and 4 bytes for a magic cookie,
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signifying that this data package contains V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data.
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If all lines are used, then there is no longer room for the bitmask. To solve this
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two different magic numbers were introduced:
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'itv0': After this magic number two unsigned longs follow. Bits 0-17 of the first
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unsigned long denote which lines of the first field are captured. Bits 18-31 of
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the first unsigned long and bits 0-3 of the second unsigned long are used for the
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second field.
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'ITV0': This magic number assumes all VBI lines are captured, i.e. it implicitly
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implies that the bitmasks are 0xffffffff and 0xf.
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After these magic cookies (and the 8 byte bitmask in case of cookie 'itv0') the
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captured VBI lines start:
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For each line the least significant 4 bits of the first byte contain the data type.
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Possible values are shown in the table below. The payload is in the following 42
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bytes.
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Here is the list of possible data types:
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.. code-block:: c
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#define IVTV_SLICED_TYPE_TELETEXT 0x1 // Teletext (uses lines 6-22 for PAL)
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#define IVTV_SLICED_TYPE_CC 0x4 // Closed Captions (line 21 NTSC)
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#define IVTV_SLICED_TYPE_WSS 0x5 // Wide Screen Signal (line 23 PAL)
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#define IVTV_SLICED_TYPE_VPS 0x7 // Video Programming System (PAL) (line 16)
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