From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001 From: root Date: Fri, 25 Dec 2015 04:40:36 +0000 Subject: initial_commit --- Documentation/video4linux/cx2341x/README.vbi | 45 ++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) create mode 100644 Documentation/video4linux/cx2341x/README.vbi (limited to 'Documentation/video4linux/cx2341x/README.vbi') diff --git a/Documentation/video4linux/cx2341x/README.vbi b/Documentation/video4linux/cx2341x/README.vbi new file mode 100644 index 00000000..5807cf15 --- /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 -- cgit v1.2.3