feat: add FFmpeg command parser with path resolution

app/ffmpeg.py

@@ -0,0 +1,43 @@
+import shlex
+from pathlib import Path
+
+# FFmpeg options that take a value (not exhaustive, covers common ones)
+OPTIONS_WITH_VALUES = {
+    "-c", "-c:v", "-c:a", "-b", "-b:v", "-b:a", "-r", "-s", "-ar", "-ac",
+    "-f", "-t", "-ss", "-to", "-vf", "-af", "-filter:v", "-filter:a",
+    "-preset", "-crf", "-qp", "-profile", "-level", "-pix_fmt", "-map",
+    "-metadata", "-disposition", "-threads", "-filter_complex",
+}
+
+
+def parse_command(command: str) -> list[str]:
+    """Parse FFmpeg command string into argument list."""
+    return shlex.split(command)
+
+
+def resolve_paths(args: list[str], data_path: str) -> list[str]:
+    """Resolve relative paths against the data directory."""
+    resolved = []
+    skip_next = False
+
+    for i, arg in enumerate(args):
+        if skip_next:
+            resolved.append(arg)
+            skip_next = False
+            continue
+
+        # Check if this is an option that takes a value
+        if arg in OPTIONS_WITH_VALUES or arg.startswith("-"):
+            resolved.append(arg)
+            if arg in OPTIONS_WITH_VALUES:
+                skip_next = True
+            continue
+
+        # This looks like a file path - resolve if relative
+        path = Path(arg)
+        if not path.is_absolute():
+            resolved.append(str(Path(data_path) / arg))
+        else:
+            resolved.append(arg)
+
+    return resolved