test_assets: add script to generate 30 sec of black frames

.gitignore

@@ -1,2 +1,5 @@
 target
 Cargo.lock
+
+test_assets/*
+!test_assets/.gitkeep

flake.nix

@@ -31,6 +31,7 @@
         pkgs.mpv
         pkgs.grcov
         pkgs.cargo-nextest
+        pkgs.ffmpeg
       ];
       RUST_SRC_PATH = "${toolchain.rust-src}/lib/rustlib/src/rust/library";
     });

setup_test_assets.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+REQUIRED_COMMANDS=(
+  "git"
+  "ffmpeg"
+)
+
+for cmd in "${REQUIRED_COMMANDS[@]}"; do
+  if ! command -v "$cmd" &> /dev/null; then
+    echo "Command '$cmd' not found. Please install it and try again."
+    exit 1
+  fi
+done
+
+ROOT_DIR=$(git rev-parse --show-toplevel)
+
+# Generate 30 seconds of 480p video with black background
+
+ffmpeg -f lavfi -i color=c=black:s=640x480:d=30 -c:v libx264 -t 30 -pix_fmt yuv420p "$ROOT_DIR/test_assets/black-background-30s-480p.mp4"