rust: create target dir, use frames/basename as decode.py

examples/main.rs

@@ -6,7 +6,6 @@ fn main() -> anyhow::Result<()> {
     let mut arg = env::args();
     arg.next(); // skip executable
     let filename = arg.next().ok_or(anyhow::anyhow!("unexpected"))?;
-    let frames = arg.next().unwrap_or("frames".into());
-    decode_to_files(&filename, &frames)?;
+    decode_to_files(&filename)?;
     Ok(())
 }