Retro footage looks

Retro footage looks

Four treatments for the user's own footage over a time range. Outside the range the clip plays clean. Inside it, the same frames come back through a shader stack. The clip keeps playing underneath, so audio and lip sync never change; only the picture is swapped.

The shader sources and uniform ranges are in references/shaders.md. They are the look (list_motion_effects has nothing like them): use them as written, and read the file before building.

Ask

If the request doesn't say, ask in one go: which look; which range (default a 4–9 s stretch starting on a cut or a pause); subtle or strong (VHS noise, CRT scan, halftone cell, copier level); for VHS the OSD date (default a plausible 90s date); for the photocopier an optional label (a zine title plus a name). Keep a range to about 10 s at most. Retro looks tire quickly, and clean footage either side makes the effect read as a choice. Don't stack two looks on one range; to go from VHS into CRT, use two back-to-back ranges with a hard cut.

Build

An effect on an overlay doesn't reach the video (overlays render in isolation), so replay the clip's own source (list_sources) in a Tella Motion document as long as the range, and lay it over the range as b-roll with a hard cut.

• Start the media node at the range start through sourceIn, in source time and in ticks (1 s = 254016000000; add the clip's trim), with fit: "cover". If the clip's base layout is padded (middle), switch it to fullscreen first so clean and treated parts frame the same.
• Add the shader with addEffect kind: "shader", bind time to seconds and key the animated uniforms linearly.
• When the look should treat extra layers too (VHS OSD, copier label), group them with the footage and put the shader on the group. Keep titles outside the halftone: halftoned text turns dotty.
• Speech stays as it is. No tape hiss or static unless asked, and then one short effect from list_library sound effects (or generate_sound_effect) on the power-on or static.
• Several ranges: build one, then duplicate_motion_document (a document plays in one place only) and re-point sourceIn and the duration.

Per look

VHS (vhs on a group of footage plus OSD). Start at bleed 10, noise 0.07. Key tracking 1 → 0.15 at 0.5 s → 0 at 0.8 s, with a 0.6 pop around 3.2 s. OSD in roboto-mono 600, #F4F4EE, letter-spacing 0.06: "PLAY" (60 px) with a drawn triangle top left, "SP" top right, time and date (56 px) stacked bottom left, all about 120 px in from the edges at 1080p. PLAY and SP leave around 3.2 s; time and date stay on, like a real camcorder.

CRT (crt on the media node, then a built-in glow: radius 28, threshold 0.62, intensity 0.55, softness 0.45). Start at curvature 0.06, scan 0.36, lines 180. Key power 0 → 1 over the first 0.35 s; snow 0 at L−0.4 s, 0.9 at L−0.15 s, 0.7 at the end. The hard cut back from static reads as a channel change. Don't power off mid-video: clean footage straight after a dying tube looks wrong.

Halftone (halftone on the media node, no time binding). Start at cell 12, amount 1, misreg 2. Key cell 48 → 12 over the first 0.7 s and back to 48 over the last 0.7 s; amount 0 → 1 over the first 0.15 s and 1 → 0 over the last 0.15 s.

Photocopier (copier on a group of footage plus label). Set the media's sampleGrid to 8 fps. Start at level 0.33, jitter 1; key scan 0 → 1 over the first 0.6 s. The optional label is a white rect (about 580×132) with a 58 px space-grotesk 700 black title and a 28 px roboto-mono subtitle, near a dark corner away from the face. Start it at 0.75 s so it never shows clean while the bar sweeps.

Vertical canvases work, since every shader reads resolution: move the OSD and label into the safe area and lower CRT lines to about 160. For a variant (ink colours, paper tint, step rate), change one constant at a time and check each at full size.

Gotchas

• Key a uniform by the field: path inspect_motion_node_properties lists after addEffect: the effect index in it is the storage index, not always the stack position.
• A shader's source can't be changed in place: remove the effect, add it again, then re-bind and re-key, since the paths can move.
• Adding the b-roll layout also creates a follow-on layout with a spring transition, which shows as a dark dip after the effect. Set it to hardCut.
• sampleGrid is a rate (numerator/denominator frames per second): 8 fps is {8, 1}. {1, 8} is one frame every 8 s, runs past the end of the source and makes every later frame fail (thumbnail_fetch_failed from that time on).
• Roboto Mono has no ▶ glyph and renders it as nothing; draw the triangle as a path.
• When editing a shader: square with x*x, not pow(negative, 2.0) (undefined on the GPU: streaks and 20 px jitter), and keep the sin-free hash; fract(sin(…) * 43758.5) breaks down at 1080p coordinates.
• Fine detail doesn't survive scaling: scanlines 160–220, halftone cells 10 px or more, grain blocks 2–3 px.
• Thresholds depend on the footage: try two copier level values side by side; a mid-tone scene floods black at 0.5. Dim archive footage relies on the halftone's built-in lift, or it prints solid black.

Check, at full size

• get_motion_frame at 1920 wide on a calm moment, and look at a 480×270 crop at 2×: scanlines, dots and grain are judged at pixel level, not from a thumbnail.
• One get_filmstrip of the clip across the range edges (just before, the first 100 ms, the middle, the last 300 ms, just after) and through the entry and exit: the treated footage starts on the same frame as the clean shot, nothing fades dark after the range, tracking settles, the power-on and static land, the dots resolve, the copier steps.
• To debug a shader, disable it (setEffect enabled: false) and return intermediate colours from a throwaway copy.