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Considering the space occupied in the vertical retrace interval by the standard 2Line VITC (e.g. 19-21), 3LineVITC fills the empty space with another line and - taking advantage of the sophistication of the Vitc readers-, does not write twice the same message but gives each line a different content, i.e. the first line carries the same Video-TC as before, the second line carries the Keycode, and the third one the Audio-TC either read on the film or entered from the ATR. The 3Line Vitc system (Aaton, Avid, Evertz, Lightworks) is the safest way to transport film data into the DNLE world.
The three consecutive lines are inserted from line 13 to 20 in NTSC (e.g.16-17-18) and from line 14 to 23 in Pal (e.g.19-20-21):
|
Time Bits |
User Bits |
CRC |
|---|---|---|---|
Line 1 |
Video-TC |
Tape Reel or Aaton Tag |
Normal |
Line 2 |
KC Prefix, Pulldown |
KC count & Frame |
Inverted |
Line 3 |
Audio-TC |
Time, Date, Cam.ID |
Nibble Inv. |
The first line is encoded with the normal SMPTE 12M CRC, so that existing VITC readers can access Video TC and AatonTags. Each of the other two lines are encoded with their own unique CRC so that there will not be any confusion for existing VITC readers which can't read them.
1 VIDEO TAPE TC - FIRST LINE
The Video tape TC is encoded into the first line of the group according to the
specifications of SMPTE 12M - 1992. The CRC is the normal SMPTE 12M CRC
encoding. The frame rate of this time code is 25 fps in PAL and 30 fps Drop
Frame or Non Drop Frame in NTSC. The user bits are encoded as 8 hexadecimal
digits, and carry the AATON Tags (address of the field in the Aaton transfer
database), or the VTR user bits, or the Video Reel ID, or any arbitrary HEX
value.
2 KEYCODE - SECOND LINE
The Keycode Information and pulldown flags are encoded into the second line of
the group. The CRC is the inverse of the SMPTE 12M CRC, i.e. the regular CRC
being '01010101' (hi to low) the Keycode CRC will be 10101010.
3 AUDIO TC - THIRD LINE
The AatonCode (or Audio TC) is encoded in the third line of the group. The CRC is
calculated the same way as the normal SMPTE 12M CRC, but carry an inverted high
order nibble, i.e. the regular CRC being '01010101' (hi to low) the Audio TC CRC
will be 10100101. The time bits of the AatonCode line contain the Audio TC and
frame count.
=end=
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