[downloader/fragment] More smooth calculations

`downloaded_bytes` is now updated on each fragment progress hook invocation

youtube_dl/downloader/fragment.py

@@ -58,6 +58,11 @@ class FragmentFD(FileDownloader):
             'frag_count': total_frags,
             'filename': ctx['filename'],
             'tmpfilename': ctx['tmpfilename'],
+            # Total complete fragments downloaded so far in bytes
+            '_complete_frags_downloaded_bytes': 0,
+            # Amount of fragment's bytes downloaded by the time of the previous
+            # frag progress hook invocation
+            '_prev_frag_downloaded_bytes': 0,
         }
         start = time.time()
         ctx['started'] = start
@@ -67,22 +72,27 @@ class FragmentFD(FileDownloader):
                 return
 
             frag_total_bytes = s.get('total_bytes') or 0
-            if s['status'] == 'finished':
-                state['downloaded_bytes'] += frag_total_bytes
-                state['frag_index'] += 1
 
             estimated_size = (
-                (state['downloaded_bytes'] + frag_total_bytes) /
+                (state['_complete_frags_downloaded_bytes'] + frag_total_bytes) /
                 (state['frag_index'] + 1) * total_frags)
             time_now = time.time()
             state['total_bytes_estimate'] = estimated_size
             state['elapsed'] = time_now - start
 
-            if s['status'] != 'finished':
+            if s['status'] == 'finished':
+                state['frag_index'] += 1
+                state['downloaded_bytes'] += frag_total_bytes - state['_prev_frag_downloaded_bytes']
+                state['_complete_frags_downloaded_bytes'] = state['downloaded_bytes']
+                state['_prev_frag_downloaded_bytes'] = 0
+            else:
+                frag_downloaded_bytes = s['downloaded_bytes']
+                state['downloaded_bytes'] += frag_downloaded_bytes - state['_prev_frag_downloaded_bytes']
                 state['eta'] = self.calc_eta(
                     start, time_now, estimated_size,
-                    state['downloaded_bytes'] + s['downloaded_bytes'])
+                    state['downloaded_bytes'])
                 state['speed'] = s.get('speed')
+                state['_prev_frag_downloaded_bytes'] = frag_downloaded_bytes
             self._hook_progress(state)
 
         ctx['dl'].add_progress_hook(frag_progress_hook)