Fix ffmpeg failing to download due to video id starting with -

src/workers.rs

@@ -481,7 +481,7 @@ async fn start_ffmpeg(
             command = command.arg("-i").arg(i.url.as_str());
         }
     }
-    match command.args(&["-c", "copy", filename]).spawn() {
+    match command.args(&["-c", "copy", "--", filename]).spawn() {
         Ok(i) => Some(i),
         Err(err) => {
             eprintln!("Failed to spawn ffmpeg: {:?}", err);