Add field `video_autonumber`

Closes #662

README.md

@@ -1160,6 +1160,7 @@ The available fields are:
  - `extractor_key` (string): Key name of the extractor
  - `epoch` (numeric): Unix epoch when creating the file
  - `autonumber` (numeric): Number that will be increased with each download, starting at `--autonumber-start`
+ - `video_autonumber` (numeric): Number that will be increased with each video
  - `n_entries` (numeric): Total number of extracted items in the playlist
  - `playlist` (string): Name or id of the playlist that contains the video
  - `playlist_index` (numeric): Index of the video in the playlist padded with leading zeros according the final index

yt_dlp/YoutubeDL.py

@@ -534,6 +534,7 @@ class YoutubeDL(object):
         self._postprocessor_hooks = []
         self._download_retcode = 0
         self._num_downloads = 0
+        self._num_videos = 0
         self._screen_file = [sys.stdout, sys.stderr][params.get('logtostderr', False)]
         self._err_file = sys.stderr
         self.params = params
@@ -1044,6 +1045,7 @@ class YoutubeDL(object):
             if info_dict.get('duration', None) is not None
             else None)
         info_dict['autonumber'] = self.params.get('autonumber_start', 1) - 1 + self._num_downloads
+        info_dict['video_autonumber'] = self._num_videos
         if info_dict.get('resolution') is None:
             info_dict['resolution'] = self.format_resolution(info_dict, default=None)
 
@@ -2275,6 +2277,7 @@ class YoutubeDL(object):
 
     def process_video_result(self, info_dict, download=True):
         assert info_dict.get('_type', 'video') == 'video'
+        self._num_videos += 1
 
         if 'id' not in info_dict:
             raise ExtractorError('Missing "id" field in extractor result')