IEC 62447-3 pdf download Helical-scan compressed digital video cassette system using 6,35 mm magnetic tape – Format D-12 – Part 3: Data stream format
7 Mapping structure
The mapping structure defines where SDTl stream blocks are mapped into SDTl frames.
An SDTl data block of the fixed-block variety (as used by this standard) is based on onestream block; the stream block in turn includes two DlF blocks and associated words, asshown in Figure 1.
In the 525/60 SDTl system,the compressed video data stream within an SDTl frame iscomposed of 3000 SDTl data blocks (6000 DlF blocks) for the 100 Mb/s structure.
In the 625/50 SDTl system，the compressed video data stream within an SDTl frame iscomposed of 3600 sDTl data blocks (7200 DIF blocks) for the 100 Mb/s structure.
7.1 Channel unit
The channel unit structure is shown in Figures 10 and 11.A channel unit is a series of SDIraster lines into which SDTl data blocks are mapped. In the case of 25 Mb/s structuretransmission, a channel unit is composed of the SDTl data blocks of one frame (see 6.2 forthe 100 Mbls structure).
A channel unit is thus composed of 750 SDTl data blocks for the 525/60 SDTl system or 900sDTl data blocks for the 625/50 SDTI system.
In the 525/60 SDTl system, a channel unit occupies 94 lines in the 270 Mb/s interface or 69lines in the 360 Mb/s interface; in the 625/50 sDTl system, a channel unit occupies 113 linesin the 270 Mbls interface or 82 lines in the 360 Mbls interface.
The remaining payload space within a channel unit should be filled with blocks with their valueset to the invalid type number 100h,as defined in SMPTE 305M.
The mapping rules are as follows.
– Channel units consist of contiguous lines with no gaps and shall not use lines 10,11,273,or 274 in the 525/60 SDTl system, or lines 6,7,319,or 320 in the 625/50 SDTl system.- The start lines in which a channel unit can be mapped are shown in Table 1.
– A channel unit shall be completely contained within an SDl video field.
One frame shall use four adjacent channel units as shown in Figures 8 and 9.The first part ofone frame shall use the first channel unit, the second part of the frame shall use the secondchannel unit,the third part of the frame shall use the third channel unit and the fourth part ofthe frame shall use the fourth channel unit.
ln the 525/60 SDTl system，3000 SDTl data blocks are mapped into 376 lines for the 270Mb/s interface or into 276 lines for the 360 Mbls interface.