Preview¶

The Preview dialogue provides interactive visual inspection of data flowing through a decode-orc pipeline. It is not a stage itself, but a UI tool that can attach to any stage that exposes preview support.

Previewing is intended for validation, and tuning. It allows you to verify timing, field order, signal integrity, and the effects of transform stages before committing to final outputs.

Preview-capable stages¶

A stage supports preview if it implements the internal preview interface (commonly exposed in code as PreviewableStage). Most source stages, all transform stages, and some sinks support preview.

Preview support generally includes:

Per-field image display
Field stepping and scrubbing
Parity (first/second field) indication
Optional overlays generated by the stage

Core preview features¶

The preview dialogue allows navigation through the pipeline output one field at a time.

Supported controls include:

Step forward / backward by field
Jump to a specific field index
Continuous playback (where supported)

Field indices always refer to the post-stage output, not the original source numbering.

Field parity display¶

The preview UI indicates whether the currently displayed field is:

First field
Second field

This is derived from the field parity hints carried through the pipeline and is especially useful when validating:

Field order correctness
Effects of the field_invert transform
Alignment after source_align

Video scaling and rendering¶

Preview rendering uses decoded sample data and applies:

Black and white levels (IRE-based)
Active video region hints
Aspect-correct scaling for display

This ensures the preview reflects how downstream sinks will interpret the signal.

Stage-specific preview behaviour¶

Some stages augment the preview dialogue with additional behaviour or controls.

Stages such as dropout_map and dropout_correct may visually indicate dropout regions.

Examples include:

Highlighted dropout areas
White-filled correction regions (when enabled via parameters)

These overlays are generated by the stage and rendered by the preview UI.

Masking stages¶

For stages such as mask_line, the preview will show masked regions directly in the rendered image, allowing immediate verification of:

Line selection
Parity-specific masking
Mask level (IRE)

Parameter override stages¶

Stages such as video_params affect how the preview is rendered by changing:

Active video boundaries
Black and white levels
Burst and active region hints

The preview dialogue always reflects the effective parameters after overrides, making it a reliable validation tool.

Preview limitations¶

Preview is non-destructive and has no effect on pipeline output.
Preview performance depends on stage complexity and pipeline position.
Some sink stages (especially hardware sinks) may not support preview.

Typical preview workflows¶

Common uses of the preview dialogue include:

Verifying capture integrity immediately after a source stage
Checking alignment after field_map and source_align
Tuning stacker parameters while observing dropout behaviour
Validating dropout correction before committing to final output
Confirming active video and masking settings

Notes on preview usage¶

Preview always shows the output of the selected stage.
When multiple branches exist, each branch can be previewed independently.
Preview does not bypass or alter pipeline execution.

The Preview dialogue is an essential companion to decode-orc’s stage-based design, providing immediate visual feedback for pipeline construction, debugging, and validation.