IEC 61904:2000 pdf free download – Video recording
4.1 Introduction
Each television field is recorded on six helical tracks.
The helical tracks contain digital data from the video channel, from four audio channels andfrom the tracking servo signals. The audio data is contained in four recorded sectors pertrack,in the middle part of each track.The video data is contained in two recorded sectorsper track,at both ends of each track. The tracking servo signals are recorded between thevideo and audio sectors. An edit gap between sectors accommodates timing errors duringediting. Figure 29 shows the arrangement of video and audio sectors and the tracking servosignals on a quartet of helical tracks for the 525/60 system and 625/50 systems.
Each sector is divided into the following elements:
a) preamble containing clock run-up sequence;
b) sync blocks containing sync pattern and identification pattern, followed by a fixed length data block with error control;
c) postamble containing sync pattern and identification pattern.4.2Labelling convention
The least significant bit is written on the left and is the first recorded to tape. The lowestnumbered byte is shown at the top-left and is the first encountered in the input data stream.Byte values are expressed in hexadecimal notation unless otherwise noted.A subscript “h”indicates a hexadecimal value.
4.3Sector details
4.3.1Sync block
The sync block format is common to both audio and video sectors.Each sync block contains async pattern (two bytes) and an inner code block (178 bytes). Each inner code block contains anidentification pattern (two bytes), data (162 bytes) and inner check bytes (14 bytes). Figure 30shows the sync block format.
4.3.3ldentification pattern
The first byte of the identification pattern (ID0) identifies a specified sync block of a helicaltrack.The second byte of the identification pattern (ID1) identifies a specified sector,track,segment and field.Figure 31 shows the track, segment and field number in a frame.
a) Length: 16 bits (two bytes)
b) Arrangement:
ID0: The sync block number(byte 2) follows a coded sequence，as shown in table 3.The last IDo code of each sector is for postamble.
4.3.6Sector post-amble
All sectors are followed by a post-amble，the length of which shall be four bytes. lt shallconsist of a sync pattern and an identification pattern.
4.4 Edit gap
The space between sectors on a track，exclusive of post-amble and preamble is used toaccommodate timing errors during editing. In an original recording the edit gap shall containthe pattern CCh. The length of the edit gap varies according to the position.
4.6Tracking servo signals
Two kinds of tracking servo signals， named the tracking pilot signal (TPS) and the trackingtiming signal (TTS), shall be recorded on the helical tracks.The locations of these signals inthe helical tracks are shown in figure 27, table 2 and figure 29.These signals should not beover-written during insert editing.
4.6.1 TPs (tracking pilot signal)
A nominal 4 MHz rectangular wave signal is recorded on track A and track C, between thefourth audio sector and the second video sector, as the TPS.The precise frequencies shall be4,13 MHz for the 525/60 system and 4,06 MHz for the 625/50 system.The length of recordingarea shall be equivalent to two sync blocks.
4.6.2TTs (tracking timing signal)
A nominal 400 kHz rectangular wave signal is recorded on track A, between the first videosector and the first audio sector, as the TTS. The precise frequencies shall be 413 kHz forthe 525/60 system and 406 kHz for the 625/50 system. The length of recording area shall beequivalent to two sync blocks.Seventeen waves are recorded on the TTS area.