Media & Data Dashboards

# Multivariant HLS manifest — a real bitrate ladder with CMAF fMP4 segments.
#EXTM3U
#EXT-X-VERSION:7
#EXT-X-STREAM-INF:BANDWIDTH=400000,RESOLUTION=426x240,CODECS="avc1.42c015,mp4a.40.2"
240p/index.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=800000,RESOLUTION=640x360,CODECS="avc1.4d401e,mp4a.40.2"
360p/index.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2500000,RESOLUTION=1280x720,CODECS="avc1.4d401f,mp4a.40.2"
720p/index.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=5000000,RESOLUTION=1920x1080,CODECS="avc1.640028,mp4a.40.2"
1080p/index.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=9000000,RESOLUTION=1920x1080,CODECS="hvc1.2.4.L123.B0"
1080p-hevc/index.m3u8

// Hybrid ABR: throughput estimate gated by buffer occupancy.
// Pure throughput oscillates on mobile; pure buffer ramps up too slowly.
const SAFETY = 0.75;          // never plan for more than 75% of measured bandwidth
const PANIC_S = 4;            // below this much buffer, drop immediately
const RAMP_S = 18;            // above this, allow one step up

export function chooseRendition(s: PlayerState, ladder: Rendition[]): Rendition {
  if (s.bufferedSeconds < PANIC_S) {
    return ladder[0];                                   // stall costs more than pixels
  }
  const budget = s.throughputBps * SAFETY;
  const affordable = ladder.filter((r) => r.bitrate <= budget);
  const best = affordable.at(-1) ?? ladder[0];

  // Step up at most one rung, and only with a healthy buffer.
  const currentIndex = ladder.indexOf(s.current);
  const bestIndex = ladder.indexOf(best);
  if (bestIndex > currentIndex) {
    return s.bufferedSeconds > RAMP_S ? ladder[currentIndex + 1] : s.current;
  }
  return best;                                          // downgrades apply immediately
}

// Multi-CDN with per-CDN health, not blind round-robin.
const CDNS = ["https://cdn-a.example", "https://cdn-b.example"];

export async function fetchSegment(path: string, attempt = 0): Promise<ArrayBuffer> {
  const cdn = CDNS[scoreboard.best()];               // ranked by recent error + latency
  const started = performance.now();
  try {
    const res = await fetch(`${cdn}${path}`, { signal: AbortSignal.timeout(6_000) });
    if (!res.ok) throw new Error(`segment_${res.status}`);
    scoreboard.success(cdn, performance.now() - started);
    return res.arrayBuffer();
  } catch (err) {
    scoreboard.failure(cdn);
    if (attempt < CDNS.length - 1) return fetchSegment(path, attempt + 1);
    throw err;                                       // player drops a rung and retries
  }
}

// Facade: zero player bytes until the user commits.
export function VideoFacade({ poster, src }: { poster: string; src: string }) {
  const [active, setActive] = useState(false);
  if (!active) {
    return (
      <button type="button" onClick={() => setActive(true)} aria-label="Play video">
        <img src={poster} alt="" width={1280} height={720} loading="lazy" />
      </button>
    );
  }
  return <LazyPlayer src={src} autoPlay />;   // dynamic import, ssr: false
}

// QoE: one event stream the media team can actually act on.
const qoe = { startedAt: performance.now(), rebuffers: 0, stalledMs: 0 };
video.addEventListener("waiting", () => { qoe.rebuffers += 1; qoe.stallStart = performance.now(); });
video.addEventListener("playing", () => {
  if (qoe.stallStart) qoe.stalledMs += performance.now() - qoe.stallStart;
  qoe.stallStart = undefined;
});
video.addEventListener("loadeddata", () =>
  rum.track("video_startup", { ms: performance.now() - qoe.startedAt, cdn, rendition }));

// 10,000 rows: ~24 in the DOM instead of 10,000.
// Node count is the cost driver — 10k rows x 8 cells is 80k elements and ~250MB.
const ROW = 36;                       // px, fixed height keeps the maths O(1)
const OVERSCAN = 6;                   // rows above and below the viewport

function useWindow(scrollTop: number, viewportH: number, total: number) {
  const first = Math.max(0, Math.floor(scrollTop / ROW) - OVERSCAN);
  const visible = Math.ceil(viewportH / ROW) + OVERSCAN * 2;
  const last = Math.min(total, first + visible);
  return { first, last, padTop: first * ROW, padBottom: (total - last) * ROW };
}

// Accessibility survives windowing only if you declare the real dimensions.
<div role="grid" aria-rowcount={total}>
  <div style={{ height: padTop }} aria-hidden="true" />
  {rows.slice(first, last).map((r, i) => (
    <div role="row" aria-rowindex={first + i + 1} key={r.id} style={{ height: ROW }}>
      <span role="gridcell">{r.name}</span>
    </div>
  ))}
  <div style={{ height: padBottom }} aria-hidden="true" />
</div>

// worker.ts — aggregate 500k rows into chart buckets, return a transferable.
// Structured clone of 50MB costs ~200ms; a transferred ArrayBuffer costs ~0ms.
self.onmessage = (e: MessageEvent<{ rows: Float64Array; buckets: number }>) => {
  const { rows, buckets } = e.data;
  const out = new Float64Array(buckets);
  const counts = new Uint32Array(buckets);

  for (let i = 0; i < rows.length; i += 2) {
    const b = Math.min(buckets - 1, (rows[i] * buckets) | 0);
    out[b] += rows[i + 1];
    counts[b] += 1;
  }
  for (let b = 0; b < buckets; b++) if (counts[b]) out[b] /= counts[b];

  self.postMessage(out, [out.buffer]);   // transfer, do not copy
};

// Ring buffer + rAF coalescing: 600 msg/s becomes at most 60 paints/s.
class Series {
  private buf: Float64Array;
  private head = 0;
  private len = 0;
  constructor(readonly cap: number) { this.buf = new Float64Array(cap); }

  push(v: number) {
    this.buf[this.head] = v;
    this.head = (this.head + 1) % this.cap;   // no allocation, no GC pressure
    this.len = Math.min(this.len + 1, this.cap);
  }
  forEach(fn: (v: number, i: number) => void) {
    const start = (this.head - this.len + this.cap) % this.cap;
    for (let i = 0; i < this.len; i++) fn(this.buf[(start + i) % this.cap], i);
  }
}

const series = new Series(1_800);            // 30 min at 1Hz
let queued = 0;

socket.onmessage = (e) => {
  series.push(JSON.parse(e.data).value);     // never setState here
  queued ||= requestAnimationFrame(() => { queued = 0; draw(series); });
};

// Backgrounded tabs get throttled to ~1Hz by the browser anyway — stop the socket
// instead of accumulating a 20-minute backlog that replays as a 3s freeze on return.
document.addEventListener("visibilitychange", () => {
  document.hidden ? socket.close() : reconnectAndBackfill(series.lastTimestamp);
});