Document the hardsub/auto-split fork

Add FORK_NOTES.md describing the new features, a README pointer, and keep
the known-good baseline encoder as contrib/dvd-safe-converter.sh (the
reference the Compatibility profile is modelled on).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

contrib/dvd-safe-converter.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Reference "DVD-safe" NTSC MPEG-2 encoder.
+#
+# This is the known-good baseline that the DeVeDe-NG hardsub fork's
+# "Compatibility (4500k)" encode profile is modelled on. It is kept here as a
+# standalone tool and as a regression reference: the fork's generated ffmpeg
+# command for the Compatibility profile (without subtitle burn-in) should
+# produce equivalent output (mpeg2video / 720x480 / 29.97fps / AC3 192k 48kHz).
+#
+# It does NOT detect or burn subtitles and does NOT split long movies; those
+# features live in the GUI fork (see FORK_NOTES.md).
+
+if [ $# -lt 1 ]; then
+  echo "Usage: $0 input_video"
+  exit 1
+fi
+
+INPUT="$1"
+BASENAME="$(basename "$INPUT")"
+NAME="${BASENAME%.*}"
+OUTPUT="${NAME}-dvdsafe.mpg"
+
+echo "Input:  $INPUT"
+echo "Output: $OUTPUT"
+echo "Encoding DVD-safe MPEG-2 (CBR 4500k)..."
+
+ffmpeg -y -i "$INPUT" \
+-vf "scale=720:480:flags=lanczos,\
+fps=30000/1001,\
+format=yuv420p,\
+setsar=1" \
+-r 30000/1001 \
+-c:v mpeg2video \
+-b:v 4500k \
+-minrate 4500k \
+-maxrate 4500k \
+-bufsize 1835k \
+-g 15 \
+-sc_threshold 0 \
+-pix_fmt yuv420p \
+-c:a ac3 \
+-b:a 192k \
+-ar 48000 \
+-ac 2 \
+"$OUTPUT"
+
+echo "Done: $OUTPUT"