VITS — vertical interval test signals¶

Vertical interval test signals are reference waveforms inserted on VBI lines so that a signal path can be measured from the picture itself. videosynth renders the standard PAL and NTSC families from their published waveform definitions.

VITS are project-wide¶

VITS live in the top-level line_injections: block and are applied to every frame of every section:

line_injections:
  vits:
    - vits_type: vits17
      target_lines: [17]

This is deliberate. A signal path's reference signals do not change halfway through a recording, and on a disc they are a property of the disc rather than of the lead-in or the programme. Declaring them once means they cannot accidentally differ between sections.

There is no section-level vits injection type; a section injection with type: vits is a validation error pointing you to the top-level block.

Available types¶

Valid vits_type values depend on the video standard. PAL types are accepted in PAL and SECAM projects, and NTSC types in NTSC and PAL-M projects.

PAL¶

`vits_type`	Signal	Recommended line
`vits17`	EBU/CCIR primary insertion test signal	17
`itu-multiburst`	ITU multiburst for PAL B, D, G, H, I	18
`uk-national`	IBA/EBU UK national insertion test signal (PAL-I)	19
`vits20`	IBA/EBU UK ITS-2 chrominance amplitude reference	20
`itu-composite`	ITU PAL composite ITS (BT.628/BT.473)	330
`itu-combination`	ITU combination ITS for PAL (BT.473)	331

NTSC and PAL-M¶

`vits_type`	Signal	Recommended line
`ntc7-composite`	NTC-7 composite ITS (EIA RS-498 / SMPTE RP 168)	17
`fcc-multiburst`	FCC multiburst (FCC Part 73 / EIA RS-498)	18
`ntc7-combination`	NTC-7 combination ITS	280
`fcc-composite`	FCC composite ITS	281
`virs`	Video Index Reference Signal (SMPTE RP 168)	None fixed — conventionally 19 / 282

Remember that line numbers are sequential across the whole frame, so 280–331 are field 2 lines.

Placement policy¶

line_injections.placement decides how strictly the validator constrains each entry's target_lines.

`standard` (default)¶

Each VITS type must sit on its broadcast recommended line, as listed above. Any other line is rejected. virs has no fixed line, so it may go on any line. This is what you want for broadcast-style test material, and it is what a project without a placement key gets.

line_injections:
  placement: standard          # or simply omit it
  vits:
    - vits_type: vits17
      target_lines: [17]

In the GUI, VITS lines are read-only under this policy — the line is a property of the signal type, not a choice.

`laserdisc`¶

On a laserdisc the broadcast VITS lines collide with the reserved address-code ranges, so IEC 60856/60857 place the test signals elsewhere:

Standard	Permitted VITS lines
PAL	19, 20, 332, 333 (IEC 60856 §9.1.3)
NTSC / PAL-M	19, 20, 282, 283 (IEC 60857 §9.1.3, §9.1.4)

Selecting this policy in the GUI seeds the spec-required set for the standard:

PAL — uk-national on 19/332, vits20 on 20/333.
NTSC / PAL-M — virs on 19/282, ntc7-composite on 20, ntc7-combination on 283.

line_injections:
  placement: laserdisc
  vits:
    - vits_type: uk-national
      target_lines: [19, 332]
    - vits_type: vits20
      target_lines: [20, 333]

laserdisc:
  disc_type: CAV

The placement policy stays in line_injections; the disc format is in the project's laserdisc: block.

`custom`¶

VITS may sit on any valid VBI line. The validator still rejects overlapping lines, and when laserdisc.disc_type is set it still rejects the reserved address-code ranges.

Use this when you are deliberately producing non-conforming material — testing how a decoder copes with a signal on the wrong line, for instance.

VITS and laserdisc together¶

The laserdisc address codes reserve whole VBI ranges, and no VITS may target a line inside them when the project sets laserdisc.disc_type, whether or not any section carries codes:

Standard	Field 1	Field 2
PAL	6–18	319–331
NTSC / PAL-M	10–18	273–281

That rules out most of the broadcast VITS lines on a disc:

PAL

`vits_type`	Line	On a disc
`vits17`	17	Rejected
`itu-multiburst`	18	Rejected
`uk-national`	19	Allowed
`vits20`	20	Allowed
`itu-composite`	330	Rejected
`itu-combination`	331	Rejected

NTSC / PAL-M

`vits_type`	Line	On a disc
`ntc7-composite`	17	Rejected
`fcc-multiburst`	18	Rejected
`ntc7-combination`	280	Rejected
`fcc-composite`	281	Rejected
`virs`	19, 282	Required

NTSC discs must carry VIRS

IEC 60857 §9.1.3 makes the Video Index Reference Signal mandatory on NTSC laserdiscs. An NTSC or PAL-M project that sets laserdisc.disc_type and has no virs entry in the project-level VITS set is a validation error.

VITS and noise measurement¶

If a section uses noise_spread_db — the two-component noise model, where white is noisier than black — the White SNR figure can only be verified from the picture if there is a VITS carrying a white reference on the measurement line: PAL frame line 19, NTSC frame line 20.

videosynth warns when spread noise is configured without such a VITS. The signal is generated correctly either way; the warning is about whether an analysis tool will be able to measure what you asked for. See Impairments.