test(sandbox): add ffmpeg-based non-Mux local live HLS source

local-live.sh generates a sliding-window demuxed CMAF/fMP4 live stream with
ffmpeg's HLS muxer (master + EXT-X-MEDIA audio group + fMP4 init/segments) to a
temp dir, served with CORS and no caching — a no-creds local live source for the
SPF engine and the hls.js/native sandbox pages. Documents the no-cache
requirement (a positive max-age on a live playlist freezes the client's window —
a server misconfiguration, not a player bug).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/sandbox/scripts/live/README.md

@@ -19,7 +19,26 @@ One broadcast yields **two** sources to test:
 Both are CMAF/fMP4, which is what the SPF MSE pipeline appends (it does not
 transmux MPEG-TS, so generic TS live test streams won't play there).
 
-## Prerequisites
+## Local source (no Mux, no creds)
+
+For a sliding-window live source without a Mux account, `local-live.sh` uses
+ffmpeg's own HLS muxer to write **demuxed CMAF/fMP4** (master + audio group +
+fMP4 init/segments) to a temp dir, served with CORS and **no caching**:
+
+```sh
+./local-live.sh                # serves http://localhost:8080/master.m3u8
+# then open the sandbox at that src (start `pnpm dev` first):
+open "http://localhost:5173/spf-segment-loading/?src=http://localhost:8080/master.m3u8&muted=true&autoplay=true&preload=auto"
+```
+
+The no-cache part is load-bearing (`http-server -c-1`): a live playlist served
+with a positive `max-age` makes reloads return a stale media-sequence, so the
+client's window never advances and playback stalls — a server misconfiguration,
+not a player bug. Mux gets this right; a plain static file server does not by
+default. (This is VOD-free and doesn't model DVR/EVENT — use the Mux flow above
+for those.)
+
+## Prerequisites (Mux flow)
 
 - `ffmpeg`, `curl`, `jq` on `PATH`.
 - A Mux access token (Mux dashboard → Settings → Access Tokens). Provide it via

apps/sandbox/scripts/live/local-live.sh

@@ -0,0 +1,56 @@
+#!/usr/bin/env bash
+# Non-Mux local live HLS source — no Mux account or creds. ffmpeg generates a
+# test pattern + tone, and its HLS muxer writes demuxed CMAF/fMP4 (master +
+# audio group + fMP4 init/segments) to a temp dir, served with CORS and NO
+# caching. SPF plays it (also the hls.js / native sandbox pages).
+#
+# A live playlist MUST be served no-cache (http-server -c-1): otherwise reloads
+# return a stale media-sequence and the client's window never advances.
+#
+# Usage: ./local-live.sh [--port N]   (default 8080). Ctrl-C to stop.
+#   Then open, e.g.:
+#   http://localhost:5173/spf-segment-loading/?src=http://localhost:8080/master.m3u8&muted=true&autoplay=true&preload=auto
+#
+# Requires: ffmpeg, npx (http-server).
+set -uo pipefail
+
+PORT=8080
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --port) PORT="$2"; shift 2 ;;
+    -h|--help) sed -n '2,13p' "$0" | sed 's/^# \{0,1\}//'; exit 0 ;;
+    *) echo "unknown argument: $1" >&2; exit 1 ;;
+  esac
+done
+
+OUT="${TMPDIR:-/tmp}/spf-local-live"
+rm -rf "$OUT"; mkdir -p "$OUT"
+
+SVR=""; FF=""
+cleanup() { kill "$SVR" "$FF" 2>/dev/null; exit 0; }
+trap cleanup INT TERM
+
+npx http-server "$OUT" -p "$PORT" --cors -c-1 -s & SVR=$!
+sleep 1
+
+echo "▶ live: http://localhost:$PORT/master.m3u8  (sliding-window, demuxed CMAF)"
+echo "  sandbox: http://localhost:5173/spf-segment-loading/?src=http://localhost:$PORT/master.m3u8&muted=true&autoplay=true&preload=auto"
+echo "  Ctrl-C to stop."
+
+# Demuxed via --var_stream_map (video variant + EXT-X-MEDIA audio group); fMP4
+# segments via -hls_segment_type fmp4; PDT for cross-track/reload timeline sync.
+ffmpeg -re \
+  -f lavfi -i testsrc=size=1280x720:rate=30 \
+  -f lavfi -i sine=frequency=440:sample_rate=48000 \
+  -map 0:v -map 1:a \
+  -c:v libx264 -preset veryfast -tune zerolatency -g 60 -keyint_min 60 -pix_fmt yuv420p \
+  -c:a aac -b:a 128k -ar 48000 \
+  -f hls -hls_time 2 -hls_list_size 6 \
+  -hls_flags independent_segments+omit_endlist+program_date_time \
+  -hls_segment_type fmp4 \
+  -hls_fmp4_init_filename 'init_%v.mp4' \
+  -hls_segment_filename "$OUT/seg_%v_%05d.m4s" \
+  -master_pl_name master.m3u8 \
+  -var_stream_map "v:0,agroup:aud,name:video a:0,agroup:aud,default:yes,name:audio" \
+  "$OUT/stream_%v.m3u8" > "$OUT/ffmpeg.log" 2>&1 & FF=$!
+wait "$FF"