[BeatportPro] Add new extractor

This extractor is for Beatport's 2-minute, low-quality track previews
only.  To obtain an entire track, you obviously have to purchase and
download it normally through the Beatport store!

Possible future improvements:
- Playlists for albums or other track-list pages
- User login to play from My Beatport, Hold Bin, or Cart

youtube_dl/extractor/beatportpro.py

@@ -0,0 +1,101 @@
+# coding: utf-8
+from __future__ import unicode_literals
+
+from .common import InfoExtractor
+
+import re
+import json
+
+
+class BeatportProIE(InfoExtractor):
+    _VALID_URL = r'https?://pro\.beatport\.com/track/.*/(?P<id>[0-9]+)'
+    _TESTS = [{
+        'url': 'https://pro.beatport.com/track/synesthesia-original-mix/5379371',
+        'md5': 'b3c34d8639a2f6a7f734382358478887',
+        'info_dict': {
+            'id': 5379371,
+            'display-id': 'synesthesia-original-mix',
+            'ext': 'mp4',
+            'title': 'Froxic - Synesthesia (Original Mix)',
+        },
+    }, {
+        'url': 'https://pro.beatport.com/track/love-and-war-original-mix/3756896',
+        'md5': 'e44c3025dfa38c6577fbaeb43da43514',
+        'info_dict': {
+            'id': 3756896,
+            'display-id': 'love-and-war-original-mix',
+            'ext': 'mp3',
+            'title': 'Wolfgang Gartner - Love & War (Original Mix)',
+        },
+    }, {
+        'url': 'https://pro.beatport.com/track/birds-original-mix/4991738',
+        'md5': 'a1fd8e8046de3950fd039304c186c05f',
+        'info_dict': {
+            'id': 4991738,
+            'display-id': 'birds-original-mix',
+            'ext': 'mp4',
+            'title': "Tos, Middle Milk, Mumblin' Johnsson - Birds (Original Mix)",
+        }
+    }]
+
+    def _real_extract(self, url):
+        track_id = self._match_id(url)
+        webpage = self._download_webpage(url, track_id)
+
+        # Extract "Playables" JSON information from the page
+        playables = self._search_regex(r'window\.Playables = ({.*?});', webpage,
+                                       'playables info', flags=re.DOTALL)
+        playables = json.loads(playables)
+
+        # Find first track with matching ID (always the first one listed?)
+        track = next(filter(lambda t: t['id'] == int(track_id), playables['tracks']))
+
+        # Construct title from artist(s), track name, and mix name
+        title = ', '.join((a['name'] for a in track['artists'])) + ' - ' + track['name']
+        if track['mix']:
+            title += ' (' + track['mix'] + ')'
+
+        # Get format information
+        formats = []
+        for ext, info in track['preview'].items():
+            if info['url'] is None:
+                continue
+            fmt = {
+                'url': info['url'],
+                'ext': ext,
+                'format_id': ext,
+                'vcodec': 'none',
+            }
+            if ext == 'mp3':
+                fmt['preference'] = 0
+                fmt['acodec'] = 'mp3'
+                fmt['abr'] = 96
+                fmt['asr'] = 44100
+            elif ext == 'mp4':
+                fmt['preference'] = 1
+                fmt['acodec'] = 'aac'
+                fmt['abr'] = 96
+                fmt['asr'] = 44100
+            formats += [fmt]
+        formats.sort(key=lambda f: f['preference'])
+
+        # Get album art as thumbnails
+        imgs = []
+        for name, info in track['images'].items():
+            if name == 'dynamic' or info['url'] is None:
+                continue
+            img = {
+                'id': name,
+                'url': info['url'],
+                'height': info['height'],
+                'width': info['width'],
+            }
+            imgs += [img]
+
+        return {
+            'id': track['id'],
+            'display-id': track['slug'],
+            'title': title,
+            'formats': formats,
+            'thumbnails': imgs,
+        }