Implement format selection in YoutubeDL

Now the IEs can set a formats field in the info_dict, with the formats ordered from worst to best quality. It's a list of dicts with the following fields:
* Mandatory: url and ext
* Optional: format and format_id

The format_id is used for choosing which formats have to be downloaded.

Now a video result is processed by the method process_video_result.

youtube_dl/YoutubeDL.py

@@ -385,13 +385,7 @@ class YoutubeDL(object):
         result_type = ie_result.get('_type', 'video') # If not given we suppose it's a video, support the default old system
         if result_type == 'video':
             ie_result.update(extra_info)
-            if 'playlist' not in ie_result:
-                # It isn't part of a playlist
-                ie_result['playlist'] = None
-                ie_result['playlist_index'] = None
-            if download:
-                self.process_info(ie_result)
-            return ie_result
+            return self.process_video_result(ie_result)
         elif result_type == 'url':
             # We have to add extra_info to the results because it may be
             # contained in a playlist
@@ -449,6 +443,64 @@ class YoutubeDL(object):
         else:
             raise Exception('Invalid result type: %s' % result_type)
 
+    def process_video_result(self, info_dict, download=True):
+        assert info_dict.get('_type', 'video') == 'video'
+
+        if 'playlist' not in info_dict:
+            # It isn't part of a playlist
+            info_dict['playlist'] = None
+            info_dict['playlist_index'] = None
+
+        # We now pick which formats have to be downloaded
+        if info_dict.get('formats') is None:
+            # There's only one format available
+            formats = [info_dict]
+        else:
+            formats = info_dict['formats']
+
+        # We check that all the formats have the format and format_id fields
+        for (i, format) in enumerate(formats):
+            if format.get('format') is None:
+                format['format'] = compat_str(i)
+            if format.get('format_id') is None:
+                format['format_id'] = compat_str(i)
+
+        if self.params.get('listformats', None):
+            self.list_formats(info_dict)
+            return
+
+        req_format = self.params.get('format', 'best')
+        formats_to_download = []
+        if req_format == 'best' or req_format is None:
+            formats_to_download = [formats[-1]]
+        elif req_format == 'worst':
+            formats_to_download = [formats[0]]
+        # The -1 is for supporting YoutubeIE
+        elif req_format in ('-1', 'all'):
+            formats_to_download = formats
+        else:
+            # We can accept formats requestd in the format: 34/10/5, we pick
+            # the first that is availble, starting from left
+            req_formats = req_format.split('/')
+            for rf in req_formats:
+                matches = filter(lambda f:f['format_id'] == rf ,formats)
+                if matches:
+                    formats_to_download = [matches[0]]
+                    break
+        if not formats_to_download:
+            raise ExtractorError(u'requested format not available')
+
+        if download:
+            if len(formats_to_download) > 1:
+                self.to_screen(u'[info] %s: downloading video in %s formats' % (info_dict['id'], len(formats_to_download)))
+            for format in formats_to_download:
+                new_info = dict(info_dict)
+                new_info.update(format)
+                self.process_info(new_info)
+        # We update the info dict with the best quality format (backwards compatibility)
+        info_dict.update(formats_to_download[-1])
+        return info_dict
+
     def process_info(self, info_dict):
         """Process a single resolved IE result."""
 
@@ -655,3 +707,17 @@ class YoutubeDL(object):
         vid_id = info_dict['extractor'] + u' ' + info_dict['id']
         with locked_file(fn, 'a', encoding='utf-8') as archive_file:
             archive_file.write(vid_id + u'\n')
+
+    def list_formats(self, info_dict):
+        formats_s = []
+        for format in info_dict.get('formats', [info_dict]):
+            formats_s.append("%s\t:\t%s\t[%s]" % (format['format_id'],
+                                                format['ext'],
+                                                format.get('format', '???'),
+                                                )
+                            )
+        if len(formats_s) != 1:
+            formats_s[0]  += ' (worst)'
+            formats_s[-1] += ' (best)'
+        formats_s = "\n".join(formats_s)
+        self.to_screen(u"[info] Available formats for %s:\nformat code\textension\n%s" % (info_dict['id'], formats_s)) 

youtube_dl/__init__.py

@@ -208,7 +208,7 @@ def parseOpts(overrideArguments=None):
 
 
     video_format.add_option('-f', '--format',
-            action='store', dest='format', metavar='FORMAT',
+            action='store', dest='format', metavar='FORMAT', default='best',
             help='video format code, specifiy the order of preference using slashes: "-f 22/17/18". "-f mp4" and "-f flv" are also supported')
     video_format.add_option('--all-formats',
             action='store_const', dest='format', help='download all available video formats', const='all')