[f4m] Tolerate missed fragments on live streams

youtube_dl/downloader/f4m.py

@@ -11,6 +11,7 @@ from .common import FileDownloader
 from .http import HttpFD
 from ..compat import (
     compat_urlparse,
+    compat_urllib_error,
 )
 from ..utils import (
     struct_pack,
@@ -389,6 +390,7 @@ class F4mFD(FileDownloader):
             if akamai_pv:
                 url += '?' + akamai_pv.strip(';')
             frag_filename = '%s-%s' % (tmpfilename, name)
+            try:
                 success = http_dl.download(frag_filename, {'url': url})
                 if not success:
                     return False
@@ -400,11 +402,26 @@ class F4mFD(FileDownloader):
                         if box_type == b'mdat':
                             dest_stream.write(box_data)
                             break
+                if live:
+                    os.remove(frag_filename)
+                else:
                     frags_filenames.append(frag_filename)
+            except (compat_urllib_error.HTTPError, ) as err:
+                if live and (err.code == 404 or err.code == 410):
+                    # We didn't keep up with the live window. Continue
+                    # with the next available fragment.
+                    msg = 'Fragment %d unavailable' % frag_i
+                    self.report_warning(msg)
+                    fragments_list = []
+                else:
+                    raise
 
             if not fragments_list and live and bootstrap_url:
                 fragments_list = self._update_live_fragments(bootstrap_url, frag_i)
-                self.to_screen('Updated available fragments: %d' % len(fragments_list))
+                total_frags += len(fragments_list)
+                if fragments_list and (fragments_list[0][1] > frag_i + 1):
+                    msg = 'Missed %d fragments' % (fragments_list[0][1] - (frag_i + 1))
+                    self.report_warning(msg)
 
         dest_stream.close()