subwave-nowplaying

Tronbyt/Tidbyt app showing the current track on a SUB/WAVE internet radio station: album art with a slow zoom/pan reveal, and four scrolling lines — track title/artist, a thin separator, the current show and host, and local time/temperature — plus a track progress bar pinned to the bottom of the 32px-wide text column. Color scheme (cyan title/artist, white show name, magenta host/progress bar) is loosely modeled on SUB/WAVE's own web now-playing display.

Not tied to any specific station — set your own station's base URL in the app's config when adding it to a device.

Configuration

• Station URL — the base URL of your SUB/WAVE instance, e.g. https://radio.example.com. No trailing slash needed (stripped automatically). No auth required — SUB/WAVE's now-playing and cover-art endpoints are public.

How it works

• GET {station_url}/api/now-playing — track title, artist, subsonic_id, DJ/station name, and stream online status. Cached 20s.

• GET {station_url}/api/cover/{subsonic_id} — album art JPEG, proxied by SUB/WAVE itself (no Navidrome credentials needed). Cached 300s.

• If the station reports streamOnline: false, shows " offline" instead of stale track info.

• If a track has no subsonic_id, or the cover fetch fails, falls back to a full-width layout with no art rather than a broken image.

• Album art gets a slow "Ken Burns" breathing effect: eases from the full frame in to a zoomed-in crop of the top-left corner, then back out, on a continuous ~60s round-trip loop (not a one-shot reveal — see below). Rendered oversized (45x45 vs. the 32x32 display slot) since animation.Scale has no visible effect on a widget whose declared size already matches its container, and scaled between 1.0 and 1.4 — only ever scaling up, never down. That's a fix for a real on-device bug: an earlier version zoomed out from a corner (scaling down from 1.0 toward ~0.71, reached via animation.Translate), which showed up on a real device as a black border cutting into the art. Empirical testing (against the actual Row layout, at native canvas size) showed the outer Box auto-fits an oversized child to its own size at Scale(1.0, 1.0) — so scaling down from there shrinks the already-fitted image further, exposing background outside its bounds. Scaling up only ever crops further into the image, which is always safe. animation.Scale's pivot defaults to the top-left corner (confirmed empirically — an explicit origin parameter was tried and had no effect at all), so there's no reliable way to zoom into any corner but that one; the effect always zooms into the top-left. Verified this doesn't blow the payload budget: measured ~280KB for a full render against the live station, comfortably under the 460KB device limit.

  Why a loop, not a one-shot reveal: a one-way version looked jumpy in practice — since the app re-renders on NOWPLAYING_TTL, each fresh render restarts its own animation from tick 0, so whatever the previous pushed image happened to be showing gets abruptly replaced by a fresh zoomed-in frame. Looping back-and-forth doesn't eliminate that (a server-side re-render always restarts at tick 0 regardless of app logic), but ending exactly where it started means the animation also loops seamlessly on-device between refreshes, which reads as far less jarring than a one-way reveal that snaps back. Considered using genuinely random per-frame content (like ormakers-tronbyt's LoRa segment, which pre-crops 60 frames directly from a high-resolution static source photo via offline Pillow processing) for a sharper zoom, but that technique fundamentally doesn't transfer here: album art is fetched live per-track at render time, and pixlet's Starlark sandbox has no image-cropping/ pixel-analysis capability at all (confirmed by checking its full module list) — so there's no way to pre-bake or crop-at-render-time from a source we don't have until the request hits the live station.

• Shows the current show name (context.activeShow.name) and host name (dj.name) below the artist, separated by a thin divider line, and the local time/temperature (context.clock/context.weather) below that — all as independently scrolling Marquee lines, confined to the 32px-wide text column next to the album art (no overlay/overlap with the art).

Known quirk — occasional Marquee glitch: pixlet's render.Marquee runs its own internal scroll-cycle animation, and stacking several Marquees of different text lengths in one Root can occasionally desync them — a line may briefly blank or show a garbled frame while another Marquee is mid-cycle. This is a real, currently-unfixed pixlet bug (there's an open FIXME: Behaviour when children themselves are animated is a bit weird in pixlet's own widget docs), not something introduced by this app. It's also not unique to this app: tronbyt/apps/apps/goosefm/goose_fm.star (an accepted official community app) stacks 3 Marquees for the same kind of now-playing info and exhibits the identical occasional glitch on close frame-by-frame inspection. In practice it's subtle enough to be easy to miss on a real, continuously-scrolling display. A custom hand-rolled scroll (via animation.Transformation + Translate, avoiding Marquee entirely) was prototyped and could fully eliminate this, but only by consolidating down to 2 scrolling lines total (title alone, everything else combined into one line) — full independent lines for every field was preferred instead, accepting the same minor quirk real Tidbyt/Tronbyt apps already ship with.

Progress bar caveat: the now-playing API reports track duration but not elapsed/remaining time, so the app tracks playback position itself — the first time it sees a given subsonic_id, it stamps the current wall-clock time in pixlet's cache, then diffs against that stamp on later renders to compute elapsed seconds. This only works correctly on a long-lived server process with a persistent cache (true for tronbyt/server's in-memory cache) — a one-shot pixlet render CLI invocation always starts a fresh process with an empty cache, so the bar will always show 0% when testing locally. This is expected, not a bug.

Note on JSON nulls: SUB/WAVE sends some fields as explicit JSON null (e.g. context.activeShow between scheduled shows) rather than omitting the key. Starlark's dict.get(key, default) only falls back to default when the key is absent — an explicit null (decoded to Starlark None) passes straight through, so this app also does ... or {} on those lookups before chaining another .get() off them, to avoid a NoneType has no .get crash.

Note on unreachable hosts: if the station URL is wrong or the host is completely unreachable (DNS failure, connection refused), http.get raises a hard error and the render fails for that cycle — this is normal pixlet/ Starlark behavior (no try/except in the language), not a bug. Only HTTP-level errors (404, 500, etc.) are something the app can catch and display a message for, which it does.

Dev/test

pixlet render subwave_nowplaying.star station_url=https://your-station.example.com
pixlet serve subwave_nowplaying.star

Deploy

Upload subwave_nowplaying.star directly through your Tronbyt server's "Upload app" button on a device's Add App page (single file, no bundled assets — no need to zip). Configure the Station URL field when adding it to your device's schedule.