Player: sharp video and subtitles at screen size; dev tools: danmaku preview, subtitle lift with a stand-in chat line

- "Sharp video and subtitles" (Settings → Player and the player settings
  card, on by default): the video output renders at the view's physical
  size (debounced, GPU rendering only), so libass, mpv's scaler and the
  shaders work at screen resolution; re-sent after media_kit's own reset
  on new video params, redrawn while paused.
- Dev builds only (Settings → About → Developer): a danmaku preview
  (DanmakuLayer: free lanes in an upper band, density cap with a queue,
  equal crossing time, outlined text, avatars, own-line frame) over the
  real player or a stand-in picture, with samples, a random stream, live
  toasts, every knob and mock subtitles; and "Lift subtitles above the
  chat line and controls": Enter opens a stand-in chat line, bottom
  subtitles move up via mpv sub-pos while it or the control bar is up.
- tool/make_sub_test.sh: a test video with a top \an8 sign, bottom
  dialogue and an SRT track.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tool/make_sub_test.sh

@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+# A 720p test video for subtitle placement and sharpness: an .ass track
+# (default) with a top-positioned sign (\an8) and bottom dialogue, and an
+# SRT track with plain bottom lines. Needs ffmpeg.
+#
+#   tool/make_sub_test.sh [out.mkv] [seconds]
+#
+# Default output: ~/Videos/starsync-sub-test.mkv, 60 s.
+set -euo pipefail
+
+out="${1:-$HOME/Videos/starsync-sub-test.mkv}"
+secs="${2:-60}"
+work="$(mktemp -d)"
+trap 'rm -rf "$work"' EXIT
+
+clock() { # seconds -> H:MM:SS.cc (ass) or HH:MM:SS,mmm (srt)
+  local s=$1 fmt=$2
+  local h=$((s / 3600)) m=$((s % 3600 / 60)) r=$((s % 60))
+  if [[ $fmt == ass ]]; then printf '%d:%02d:%02d.00' $h $m $r; else printf '%02d:%02d:%02d,000' $h $m $r; fi
+}
+
+lines=(
+  "Bottom dialogue: the controls should never cover this line."
+  "A second line of dialogue,\\Nsplit over two rows."
+  "日本語の字幕もここに表示されます。"
+  "Short one."
+  "The sign at the top must stay where it is."
+)
+
+{
+  cat <<'EOF'
+[Script Info]
+ScriptType: v4.00+
+PlayResX: 1280
+PlayResY: 720
+WrapStyle: 0
+ScaledBorderAndShadow: yes
+
+[V4+ Styles]
+Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
+Style: Default,Noto Sans,48,&H00FFFFFF,&H000000FF,&H00000000,&H80000000,0,0,0,0,100,100,0,0,1,2.5,1,2,40,40,36,1
+Style: Sign,Noto Serif,40,&H0000E5FF,&H000000FF,&H00301000,&H00000000,1,0,0,0,100,100,1,0,1,3,0,8,40,40,30,1
+
+[Events]
+Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
+EOF
+  echo "Dialogue: 0,$(clock 0 ass),$(clock "$secs" ass),Sign,,0,0,0,,{\\an8}TOP SIGN (\\\\an8): stays put"
+  i=0
+  for ((t = 0; t < secs; t += 4)); do
+    echo "Dialogue: 0,$(clock $t ass),$(clock $((t + 4)) ass),Default,,0,0,0,,${lines[$((i % ${#lines[@]}))]}"
+    i=$((i + 1))
+  done
+} >"$work/subs.ass"
+
+{
+  n=1
+  for ((t = 0; t < secs; t += 4)); do
+    echo $n
+    echo "$(clock $t srt) --> $(clock $((t + 4)) srt)"
+    echo "Plain SRT line $n at the bottom"
+    echo
+    n=$((n + 1))
+  done
+} >"$work/subs.srt"
+
+mkdir -p "$(dirname "$out")"
+ffmpeg -hide_banner -loglevel error -y \
+  -f lavfi -i "testsrc2=size=1280x720:rate=24:duration=$secs" \
+  -f lavfi -i "sine=frequency=440:duration=$secs" \
+  -i "$work/subs.ass" -i "$work/subs.srt" \
+  -map 0:v -map 1:a -map 2 -map 3 \
+  -c:v libx264 -preset veryfast -crf 23 -pix_fmt yuv420p -c:a aac -b:a 96k \
+  -c:s:0 ass -c:s:1 srt \
+  -metadata:s:s:0 title="ASS: top sign + bottom dialogue" -metadata:s:s:0 language=eng \
+  -metadata:s:s:1 title="SRT: bottom lines" -metadata:s:s:1 language=eng \
+  -disposition:s:0 default -disposition:s:1 0 \
+  "$out"
+echo "$out"