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Commit | Line | Data |
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29900661 HV |
1 | |
2 | Format of embedded V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data | |
3 | ========================================================= | |
4 | ||
5 | This document describes the V4L2_MPEG_STREAM_VBI_FMT_IVTV format of the VBI data | |
6 | embedded in an MPEG-2 program stream. This format is in part dictated by some | |
7 | hardware limitations of the ivtv driver (the driver for the Conexant cx23415/6 | |
8 | chips), in particular a maximum size for the VBI data. Anything longer is cut | |
9 | off when the MPEG stream is played back through the cx23415. | |
10 | ||
11 | The advantage of this format is it is very compact and that all VBI data for | |
12 | all lines can be stored while still fitting within the maximum allowed size. | |
13 | ||
14 | The stream ID of the VBI data is 0xBD. The maximum size of the embedded data is | |
15 | 4 + 43 * 36, which is 4 bytes for a header and 2 * 18 VBI lines with a 1 byte | |
16 | header and a 42 bytes payload each. Anything beyond this limit is cut off by | |
17 | the cx23415/6 firmware. Besides the data for the VBI lines we also need 36 bits | |
18 | for a bitmask determining which lines are captured and 4 bytes for a magic cookie, | |
19 | signifying that this data package contains V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data. | |
20 | If all lines are used, then there is no longer room for the bitmask. To solve this | |
21 | two different magic numbers were introduced: | |
22 | ||
23 | 'itv0': After this magic number two unsigned longs follow. Bits 0-17 of the first | |
24 | unsigned long denote which lines of the first field are captured. Bits 18-31 of | |
25 | the first unsigned long and bits 0-3 of the second unsigned long are used for the | |
26 | second field. | |
27 | ||
28 | 'ITV0': This magic number assumes all VBI lines are captured, i.e. it implicitly | |
29 | implies that the bitmasks are 0xffffffff and 0xf. | |
30 | ||
31 | After these magic cookies (and the 8 byte bitmask in case of cookie 'itv0') the | |
32 | captured VBI lines start: | |
33 | ||
34 | For each line the least significant 4 bits of the first byte contain the data type. | |
35 | Possible values are shown in the table below. The payload is in the following 42 | |
36 | bytes. | |
37 | ||
38 | Here is the list of possible data types: | |
39 | ||
40 | #define IVTV_SLICED_TYPE_TELETEXT 0x1 // Teletext (uses lines 6-22 for PAL) | |
41 | #define IVTV_SLICED_TYPE_CC 0x4 // Closed Captions (line 21 NTSC) | |
42 | #define IVTV_SLICED_TYPE_WSS 0x5 // Wide Screen Signal (line 23 PAL) | |
43 | #define IVTV_SLICED_TYPE_VPS 0x7 // Video Programming System (PAL) (line 16) | |
44 | ||
45 | Hans Verkuil <hverkuil@xs4all.nl> |