Show name of downloader in verbose log

Closes #3703

yt_dlp/YoutubeDL.py

@@ -2833,7 +2833,7 @@ class YoutubeDL:
             urls = '", "'.join(
                 (f['url'].split(',')[0] + ',<data>' if f['url'].startswith('data:') else f['url'])
                 for f in info.get('requested_formats', []) or [info])
-            self.write_debug('Invoking downloader on "%s"' % urls)
+            self.write_debug(f'Invoking {fd.FD_NAME} downloader on "{urls}"')
 
         # Note: Ideally info should be a deep-copied so that hooks cannot modify it.
         # But it may contain objects that are not deep-copyable

yt_dlp/downloader/common.py

@@ -98,6 +98,10 @@ class FileDownloader:
     def to_screen(self, *args, **kargs):
         self.ydl.to_screen(*args, quiet=self.params.get('quiet'), **kargs)
 
+    @property
+    def FD_NAME(self):
+        return re.sub(r'(?<!^)(?=[A-Z])', '_', type(self).__name__[:-2]).lower()
+
     @staticmethod
     def format_seconds(seconds):
         time = timetuple_from_msec(seconds * 1000)

yt_dlp/downloader/f4m.py

@@ -256,8 +256,6 @@ class F4mFD(FragmentFD):
     A downloader for f4m manifests or AdobeHDS.
     """
 
-    FD_NAME = 'f4m'
-
     def _get_unencrypted_media(self, doc):
         media = doc.findall(_add_ns('media'))
         if not media:

yt_dlp/downloader/ism.py

@@ -230,8 +230,6 @@ class IsmFD(FragmentFD):
     Download segments in a ISM manifest
     """
 
-    FD_NAME = 'ism'
-
     def real_download(self, filename, info_dict):
         segments = info_dict['fragments'][:1] if self.params.get(
             'test', False) else info_dict['fragments']

yt_dlp/downloader/mhtml.py

@@ -9,8 +9,6 @@ from ..version import __version__ as YT_DLP_VERSION
 
 
 class MhtmlFD(FragmentFD):
-    FD_NAME = 'mhtml'
-
     _STYLESHEET = """\
 html, body {
     margin: 0;

yt_dlp/downloader/niconico.py

@@ -9,8 +9,6 @@ from ..utils import sanitized_Request
 class NiconicoDmcFD(FileDownloader):
     """ Downloading niconico douga from DMC with heartbeat """
 
-    FD_NAME = 'niconico_dmc'
-
     def real_download(self, filename, info_dict):
         self.to_screen('[%s] Downloading from DMC' % self.FD_NAME)
 

yt_dlp/downloader/youtube_live_chat.py

@@ -10,8 +10,6 @@ from ..utils import RegexNotFoundError, dict_get, int_or_none, try_get
 class YoutubeLiveChatFD(FragmentFD):
     """ Downloads YouTube live chats fragment by fragment """
 
-    FD_NAME = 'youtube_live_chat'
-
     def real_download(self, filename, info_dict):
         video_id = info_dict['video_id']
         self.to_screen('[%s] Downloading live chat' % self.FD_NAME)