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Betamax

Window styling

Betamax draws a synthetic window around the terminal: a backdrop margin, a window bar with an optional title, an outline, rounded corners, and a shadow. A preset picks all of these at once, and individual Set commands adjust them.

Decoration changes generated images only. State JSON and the program under test see the same terminal. The margin, window bar, and caption row do take space from Width and Height, so more decoration leaves a smaller PTY grid.

Presets

Section titled “Presets”
Set Preset Framed
Framed preset: window bar with dots and title, rounded window, gradient, shadow
Framed: the default
Inset preset: rounded panel with an outline on a solid backdrop
Inset: a compact panel
Bare preset: terminal content with no decoration
Bare: terminal content only
Default-0.1 preset: Aardvark Blue with 60px padding and no window
Default-0.1: the 0.1 defaults
Preset Use it for
Default The current default, which is Framed. A later release may select another look.
Framed README and release media: bar, rounded window, outline, gradient, and shadow.
Inset Docs and review images: a rounded, outlined panel on a solid surface.
Bare Undecorated terminal content with the same sizing and typography.
Default-0.1 Existing tapes that should keep Betamax 0.1 sizing, theme, and padding.

Explicit Set values override the preset no matter which line comes first, so a tape can start from a preset and change one thing:

Set Preset Inset
Set Theme "GitHub Light Default"
Set BorderRadius 6

Framed and Inset derive their backdrop and bar colors from the final theme: a slightly lighter and darker version of a dark background, or two darker shades of a light one. Change the theme and the frame follows; set MarginFill or WindowBarColor to choose colors yourself. The preset table lists every resolved value.

Margin and backdrop

Section titled “Margin and backdrop”

Margin is the space between the window and the image edge. MarginFill paints it with a color, a linear gradient, a picture, or nothing at all:

Set Margin 44
Set MarginFill "#232640"
Set MarginFill "linear(to: bottom-right, #4d5b9e 0%, #232640 42%, #0f101a 100%)"
Set MarginFill "image(backdrop.jpg)"
Set MarginFill transparent
A window and caption on a blue-to-black diagonal gradient backdrop

Gradients are linear(...) with an optional direction and two or more stops. Without a direction they run top to bottom; to: <side-or-corner> and angle: <n>deg change that. Stops may carry percentages, and if one does, they all must. This is Betamax syntax, not CSS: no radial gradients. See Margin fill for the grammar.

Per-side margins

Section titled “Per-side margins”

A string sets each side separately, in CSS order: "top right bottom left", or fewer values that repeat as in CSS. Use it to move the window off-centre or reserve room for a caption or a logo:

Set Margin "40 200 120 40"

See margin-sides.tape.

Images

Section titled “Images”

A bare path such as Set MarginFill "backdrop.jpg" stretches the picture over the output, as VHS does. image(backdrop.jpg) keeps its aspect ratio and crops to cover; add contain, tile, or stretch as a second argument to change that. Relative paths are tried from the working directory, then beside the tape. See Image margin.

Transparency

Section titled “Transparency”

Set MarginFill transparent leaves the backdrop clear, so the window and its shadow sit on whatever page shows the image. #rrggbbaa colors tint the page, and transparent works as a gradient stop:

Set MarginFill transparent
Set MarginFill "#0f101a80"
Set MarginFill "linear(to: bottom, #4d5b9e, transparent)"

This image has a transparent margin. Switch the site between light and dark to see the page behind it change:

A framed window with a soft shadow and no backdrop, over the page background

The window, bar, border, and terminal stay opaque. The shadow becomes translucent black, which darkens any page. PNG, Screenshot, PNG sequences, WebP, and WebM keep full alpha. GIF has only on/off transparency, so the soft shadow and antialiased corners drop out. MP4 has no alpha and is rejected before the shell starts. Captions keep their theme colors, so check them against the page they will sit on. See Transparent margin.

Window bar

Section titled “Window bar”
Set WindowBar RingsRight
Set WindowBarColor "#0f101a"
Window bar with dots on the left and a centered title
Colorful with a WindowTitle
Window bar with dots on the right and a darker bar color
RingsRight with a darker WindowBarColor

Any non-empty WindowBar value draws red, yellow, and green dots on the left. Values ending in Right, such as ColorfulRight or RingsRight, put them on the right. Set WindowBar "" removes the bar and its title. WindowBarSize sets its height, 30 by default. WindowBarColor accepts #rrggbb and otherwise follows the preset’s theme-derived surface.

Window titles

Section titled “Window titles”
Set WindowTitle "jk — log"

The title is centered on the bar in FontFamily at 40% of the bar height. It never overlaps the dots, and long titles end with …. Its color is picked automatically for at least 4.5:1 contrast with the bar; set WindowTitleColor "#rrggbb" to choose one.

Programs can set the title too. Like a real terminal, Betamax follows OSC 0 and OSC 2 title sequences, so a TUI that names its current view shows that name in the recording. A runtime WindowTitle command takes the title back, and whichever assignment came last wins:

Window title changing as the app and the tape alternately set it 
Set WindowTitle "title set by tape"


Type "printf '\033]2;title set by app\007'"
Enter
Sleep 1s


WindowTitle "title reset by tape"
Sleep 1s

Set WindowTitleFromTerminal false to keep only the tape’s title. Each title change keeps its own frame in the animation, even when the app changes it several times in one burst. State JSON always records the app’s own title in title, independent of what the bar displays. See Following app titles.

Border, corners, and shadow

Section titled “Border, corners, and shadow”
A window with a custom bar color, title, outline, continuous corners, and shadow 
Set BorderRadius 11
Set WindowBorder 1
Set WindowBorderOpacity 0.28
Set Shadow true
Set ShadowBlur 28
Set ShadowOffset 9
  • Corners: BorderRadius uses continuous corners that ease into the straight edges, like macOS windows. The window, border, and shadow share the same shape. 0 keeps square corners.
  • Border: WindowBorder is a thin outline around the bar and terminal together, in pixels. WindowBorderColor defaults to auto, which picks white or black against the theme background, and WindowBorderOpacity defaults to 0.15. 0 removes it.
  • Shadow: a soft black shadow below the window. ShadowBlur is a CSS-style blur radius, ShadowOffset moves it down (or up, if negative), and ShadowOpacity sets its strength. It needs a margin to show in: leave at least ShadowBlur + ShadowOffset pixels so it fades out before the image edge. It shows best on a gradient or a backdrop lighter than black.

Decoration never covers terminal cells. The window grows outward into the margin to make room for its border and corners; if the margin is too small, the tape fails at startup and asks for a larger Margin or smaller BorderRadius.

A complete look

Section titled “A complete look”

This tape uses the bundled SP Night theme with a custom gradient, bar color, and title. Start from a preset, then set the details:

Set Theme "sp_night_noite"
Set Width 900
Set Height 360
Set Padding 24
Set Margin 44
Set MarginFill "linear(#232640, #0f101a)"
Set WindowBarColor "#0f101a"
Set WindowTitle "SP Night — Noite Paulista"
SP Night palette in a framed window on a dark blue gradient with a centered title

Examples

Section titled “Examples”

Each tape renders one feature on its own: