diff --git a/youtube_dl/downloader/common.py b/youtube_dl/downloader/common.py
index 1cdba89cd..362358508 100644
--- a/youtube_dl/downloader/common.py
+++ b/youtube_dl/downloader/common.py
@@ -58,7 +58,7 @@ class FileDownloader(object):
     _TEST_FILE_SIZE = 10241
     params = None
 
-    def __init__(self, ydl, params):
+    def __init__(self, ydl, params: dict):
         """Create a FileDownloader object with the given options."""
         self.ydl = ydl
         self._progress_hooks = []
diff --git a/youtube_dl/downloader/external.py b/youtube_dl/downloader/external.py
index 072f7c1fe..0ed7907b2 100644
--- a/youtube_dl/downloader/external.py
+++ b/youtube_dl/downloader/external.py
@@ -216,8 +216,8 @@ class Aria2pFD(ExternalFD):
     '''
     AVAILABLE_OPT = 'show'
 
-    def _call_downloader(self, tmpfilename, info_dict):
-        try:    
+    def _call_downloader(self, tmpfilename: str, info_dict: dict):
+        try:
             aria2 = aria2p.API(
                 aria2p.Client(
                     host="http://localhost",
@@ -238,20 +238,15 @@ class Aria2pFD(ExternalFD):
         options["min-split-size"] = "1M"
         options["max-connection-per-server"] = 4
         options["auto-file-renaming"] = "false"
-        dn = os.path.dirname(tmpfilename)
-        if dn:
-            options["dir"] = dn
+        download_dir = os.path.dirname(tmpfilename)
+        if download_dir:
+            options["dir"] = download_dir
         else:
             options["dir"] = os.path.abspath('.')
         options["out"] = os.path.basename(tmpfilename)
         options["header"] = []
         for key, val in info_dict['http_headers'].items():
             options["header"].append(f"{key}: {val}")
-        # cmd += self._option('--interface', 'source_address')
-        # cmd += self._option('--all-proxy', 'proxy')
-        # cmd += self._bool_option('--check-certificate', 'nocheckcertificate', 'false', 'true', '=')
-        # cmd += self._bool_option('--remote-time', 'updatetime', 'true', 'false', '=')
-        # cmd += ["call", "adduri", "-J", "[[\"{}\"], {}]".format(info_dict['url'], str(options)).replace("'", '"')]
         download = aria2.add_uris([info_dict['url']], options)
         while download.status == "active":
             download = aria2.get_download(download.gid)