[dispeak] improve mp4 bitrate extraction

youtube_dl/extractor/dispeak.py

@@ -58,10 +58,17 @@ class DigitallySpeakingIE(InfoExtractor):
             stream_name = xpath_text(a_format, 'streamName', fatal=True)
             video_path = re.match(r'mp4\:(?P<path>.*)', stream_name).group('path')
             url = video_root + video_path
-            vbr = xpath_text(a_format, 'bitrate')
+            bitrate = xpath_text(a_format, 'bitrate')
+            tbr = int_or_none(bitrate)
+            vbr = int_or_none(self._search_regex(
+                r'-(\d+)\.mp4', video_path, 'vbr', default=None))
+            abr = tbr - vbr if tbr and vbr else None
             video_formats.append({
+                'format_id': bitrate,
                 'url': url,
-                'vbr': int_or_none(vbr),
+                'tbr': tbr,
+                'vbr': vbr,
+                'abr': abr,
             })
         return video_formats