restreamer: When generating playlists, include discontinuities, timestamps and endlist

This fills out the incomplete playlist generation functionality to handle holes
and communicate extra information. See comments for details.

restreamer/restreamer/generate_hls.py

@@ -24,6 +24,7 @@ def generate_media(segments, base_url):
 	"""Generate a media playlist from a list of segments as returned by common.get_best_segments().
 	Segments are specified as hour/name.ts relative to base_url.
 	"""
+
 	# We have to pick a "target duration". in most circumstances almost all segments
 	# will be of that duration, so we get the most common duration out of all the segments
 	# and use that.
@@ -34,14 +35,45 @@ def generate_media(segments, base_url):
 		((target_duration, _),) = Counter(segment.duration for segment in non_none_segments).most_common(1)
 	else:
 		target_duration = datetime.timedelta(seconds=6)
+
 	lines = [
 		"#EXTM3U",
 		"#EXT-X-TARGETDURATION:{:.3f}".format(target_duration.total_seconds()),
 	]
+
+	# Note and remove any trailing None from the segment list - this indicates there is a hole
+	# at the end, which means we should mark the stream as incomplete but not include a discontinuity.
+	if segments and segments[-1] is None:
+		incomplete = True
+		segments = segments[:-1]
+	else:
+		incomplete = False
+
+	# Remove any leading None from the segment list - this indicates there is a hole at the start,
+	# which isn't actually meaningful in any way to us.
+	# Note that in the case of segments = [None], we already removed it when we removed the trailing
+	# None, and segments is now []. This is fine.
+	if segments and segments[0] is None:
+		segments = segments[1:]
+
 	for segment in segments:
-		# TODO handle missing bits, stream endings, other stuff
-		if segment is not None:
+		if segment is None:
+			# Discontinuity. Adding this tag tells the client that we've missed something
+			# and it should start decoding fresh on the next segment. This is required when
+			# someone stops/starts a stream and a good idea if we're missing a segment in a
+			# continuous stream.
+			lines.append("#EXT-X-DISCONTINUITY")
+		else:
+			# Each segment has two prefixes: timestamp and duration.
+			# This tells the client exactly what time the segment represents, which is important
+			# for the editor since it needs to describe cut points in these times.
 			path = '/'.join(segment.path.split('/')[-2:])
+			lines.append("#EXT-X-PROGRAM-DATE-TIME:{}".format(segment.start.strftime("%Y-%m-%dT%H:%M:%S.%fZ")))
 			lines.append("#EXTINF:{:.3f},live".format(segment.duration.total_seconds()))
 			lines.append(urllib.quote(os.path.join(base_url, path)))
+
+	# If stream is complete, add an ENDLIST marker to show this.
+	if not incomplete:
+		lines.append("#EXT-X-ENDLIST")
+
 	return "\n".join(lines) + '\n'