forked from luck/tmp_suning_uos_patched
46 lines
2.3 KiB
Plaintext
46 lines
2.3 KiB
Plaintext
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Format of embedded V4L2_MPEG_STREAM_VBI_FMT_IVTV VBI data
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=========================================================
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This document 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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#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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Hans Verkuil <hverkuil@xs4all.nl>
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