Add whisper.cpp engine with Vulkan GPU support (AMD/Intel/NVIDIA)

- meetrec.py: engine layer with a common transcribe() contract;
  WhisperCppEngine shells out to whisper-cli, GGML + Silero VAD models
  auto-download to ~/.cache/meetrec; faster-whisper import now lazy;
  new --engine CLI option
- meetrec_gui.py: Engine dropdown; Device/Compute greyed out for
  whisper-cpp; model reload keyed on (engine, model, device, compute)
- install.sh: --whisper-cpp builds whisper.cpp with -DWHISPER_VULKAN=ON,
  installs whisper-cli into the prefix and wires WHISPER_CPP_BIN via a
  generated whisper-cpp.env; build failures degrade to a warning
- launchers source whisper-cpp.env; README documents engines
- Recorder.stop() is now idempotent (GUI close path called it twice)

install.sh

@@ -4,6 +4,7 @@
 #
 # Usage:
 #   ./install.sh                  install, pre-downloading the 'small' model
+#   ./install.sh --whisper-cpp    also build whisper.cpp (Vulkan GPU backend)
 #   ./install.sh --model base     pre-download a different Whisper model
 #   ./install.sh --no-model       skip the model pre-download
 #   ./install.sh --uninstall      remove everything the installer created
@@ -26,6 +27,7 @@ SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 MODEL="small"
 DOWNLOAD_MODEL=1
 UNINSTALL=0
+WHISPER_CPP=0
 
 while [ $# -gt 0 ]; do
     case "$1" in
@@ -35,9 +37,10 @@ while [ $# -gt 0 ]; do
             shift 2
             ;;
         --no-model) DOWNLOAD_MODEL=0; shift ;;
+        --whisper-cpp) WHISPER_CPP=1; shift ;;
         --uninstall) UNINSTALL=1; shift ;;
         -h|--help)
-            sed -n '2,13p' "$0" | sed 's/^# \{0,1\}//'
+            sed -n '2,14p' "$0" | sed 's/^# \{0,1\}//'
             exit 0
             ;;
         *)
@@ -58,7 +61,7 @@ if [ "$UNINSTALL" = 1 ]; then
     if command -v update-desktop-database >/dev/null 2>&1; then
         update-desktop-database "$DESKTOP_DIR" 2>/dev/null || true
     fi
-    echo "Done. (Whisper models remain in ~/.cache/huggingface — remove that if you want them gone.)"
+    echo "Done. (Whisper models remain in ~/.cache/huggingface and ~/.cache/meetrec — remove those if you want them gone.)"
     exit 0
 fi
 
@@ -101,10 +104,52 @@ fi
 echo "==> Installing Python dependencies (numpy, sounddevice, faster-whisper, pyside6)"
 "$VENV/bin/pip" install -r "$APP_DIR/requirements.txt"
 
+# ----------------------------------------------------------- whisper.cpp build
+
+if [ "$WHISPER_CPP" = 1 ]; then
+    echo "==> Building whisper.cpp (Vulkan GPU backend)"
+    build_ok=1
+    for t in git cmake g++ make; do
+        command -v "$t" >/dev/null 2>&1 || {
+            echo "warning: '$t' not found — skipping the whisper.cpp build." >&2
+            build_ok=0
+        }
+    done
+    if [ "$build_ok" = 1 ]; then
+        if command -v pkg-config >/dev/null 2>&1 && ! pkg-config --exists vulkan; then
+            echo "warning: Vulkan dev headers not found — the build may fail."
+            echo "         On Arch: sudo pacman -S vulkan-headers"
+        fi
+        SRC="$APP_DIR/src/whisper.cpp"
+        if [ -d "$SRC/.git" ]; then
+            git -C "$SRC" pull --ff-only || true
+        else
+            git clone --depth 1 https://github.com/ggml-org/whisper.cpp "$SRC"
+        fi
+        # The GPU engine is optional: a failed build must not leave the core
+        # install half-done, so degrade to a warning and continue.
+        if ! (cmake -S "$SRC" -B "$SRC/build" -DCMAKE_BUILD_TYPE=Release \
+                -DWHISPER_VULKAN=ON \
+              && cmake --build "$SRC/build" -j"$(nproc)" \
+              && install -Dm755 "$SRC/build/bin/whisper-cli" \
+                    "$PREFIX/share/meetrec/whisper-cpp/bin/whisper-cli"); then
+            echo "warning: whisper.cpp build failed — continuing without the GPU engine." >&2
+            echo "         faster-whisper (CPU) still works; retry the build later with ./install.sh --whisper-cpp" >&2
+        fi
+    fi
+fi
+
 echo "==> Installing launchers into $BIN_DIR"
 install -m 0755 "$SCRIPT_DIR/bin/meetrec" "$BIN_DIR/meetrec"
 install -m 0755 "$SCRIPT_DIR/bin/meetrec-cli" "$BIN_DIR/meetrec-cli"
 
+if [ -x "$PREFIX/share/meetrec/whisper-cpp/bin/whisper-cli" ]; then
+    printf 'WHISPER_CPP_BIN="%s"\n' \
+        "$PREFIX/share/meetrec/whisper-cpp/bin/whisper-cli" \
+        > "$APP_DIR/whisper-cpp.env"
+    echo "    (whisper.cpp engine installed — select 'whisper-cpp' to use the GPU)"
+fi
+
 echo "==> Installing XDG desktop entry"
 install -m 0644 "$SCRIPT_DIR/share/applications/meetrec.desktop" \
     "$DESKTOP_DIR/meetrec.desktop"
@@ -120,6 +165,20 @@ WhisperModel("$MODEL", device="cpu", compute_type="int8")
 EOF
 fi
 
+if [ "$WHISPER_CPP" = 1 ] && [ "$DOWNLOAD_MODEL" = 1 ]; then
+    echo "==> Pre-downloading whisper.cpp model ggml-$MODEL.bin"
+    CACHE="$HOME/.cache/meetrec/whisper-cpp"
+    mkdir -p "$CACHE"
+    if command -v curl >/dev/null 2>&1; then
+        curl -fL --retry 3 -C - -o "$CACHE/ggml-$MODEL.bin.part" \
+            "https://huggingface.co/ggerganov/whisper.cpp/resolve/main/ggml-$MODEL.bin" \
+            && mv "$CACHE/ggml-$MODEL.bin.part" "$CACHE/ggml-$MODEL.bin" \
+            || echo "warning: ggml model download failed — it will retry on first use."
+    else
+        echo "warning: curl not found — skipping ggml model pre-download"
+    fi
+fi
+
 # ----------------------------------------------------------------- summary
 
 echo