Merge pull request #136 from ekimekim/mike/cut-maybe-stream

full cut: Optionally use seekable file OR directly stream

common/common/segments.py

@@ -295,8 +295,9 @@ def ffmpeg_cut_segment(segment, cut_start=None, cut_end=None):
 def ffmpeg_cut_stdin(output_file, cut_start, duration, encode_args):
 	"""Return a Popen object which is ffmpeg cutting from stdin.
 	This is used when doing a full cut.
-	Note the explicit output file object instead of using a pipe,
-	because most video formats require a seekable file.
+	If output_file is not subprocess.PIPE,
+	uses explicit output file object instead of using a pipe,
+	because some video formats require a seekable file.
 	"""
 	args = [
 		'ffmpeg',
@@ -304,7 +305,11 @@ def ffmpeg_cut_stdin(output_file, cut_start, duration, encode_args):
 		'-i', '-',
 		'-ss', cut_start,
 		'-t', duration,
-	] + list(encode_args) + [
+	] + list(encode_args)
+	if output_file is subprocess.PIPE:
+		args.append('-') # output to stdout
+	else:
+		args += [
 			# We want ffmpeg to write to our tempfile, which is its stdout.
 			# However, it assumes that '-' means the output is not seekable.
 			# We trick it into understanding that its stdout is seekable by
@@ -401,41 +406,67 @@ def fast_cut_segments(segments, start, end):
 					yield chunk
 
 
-@timed('cut', type='full', normalize=lambda _, segments, start, end, encode_args: (end - start).total_seconds())
-def full_cut_segments(segments, start, end, encode_args):
+def feed_input(segments, pipe):
+	"""Write each segment's data into the given pipe in order.
+	This is used to provide input to ffmpeg in a full cut."""
+	for segment in segments:
+		with open(segment.path) as f:
+			try:
+				shutil.copyfileobj(f, pipe)
+			except OSError as e:
+				# ignore EPIPE, as this just means the end cut meant we didn't need all it
+				if e.errno != errno.EPIPE:
+					raise
+	pipe.close()
+
+
+@timed('cut',
+	type=lambda _, segments, start, end, encode_args, stream=False: "full-streamed" if stream else "full-buffered",
+	normalize=lambda _, segments, start, end, *a, **k: (end - start).total_seconds()),
+)
+def full_cut_segments(segments, start, end, encode_args, stream=False):
+	"""If stream=true, assume encode_args gives a streamable format,
+	and begin returning output immediately instead of waiting for ffmpeg to finish
+	and buffering to disk."""
 	# how far into the first segment to begin
 	cut_start = max(0, (start - segments[0].start).total_seconds())
 	# duration
 	duration = (end - start).total_seconds()
 
 	ffmpeg = None
+	input_feeder = None
 	try:
-		# Most ffmpeg output formats require a seekable file.
+
+		if stream:
+			# When streaming, we can just use a pipe
+			tempfile = subprocess.PIPE
+		else:
+			# Some ffmpeg output formats require a seekable file.
 			# For the same reason, it's not safe to begin uploading until ffmpeg
 			# has finished. We create a temporary file for this.
 			tempfile = TemporaryFile()
+
 		ffmpeg = ffmpeg_cut_stdin(tempfile, cut_start, duration, encode_args)
+		input_feeder = gevent.spawn(feed_input, segments, ffmpeg.stdin)
 
-		# stream the input
-		for segment in segments:
-			with open(segment.path) as f:
-				try:
-					shutil.copyfileobj(f, ffmpeg.stdin)
-				except OSError as e:
-					# ignore EPIPE, as this just means the end cut meant we didn't need all input
-					if e.errno != errno.EPIPE:
-						raise
-		ffmpeg.stdin.close()
+		# When streaming, we can return data as it is available
+		if stream:
+			for chunk in read_chunks(ffmpeg.stdout):
+				yield chunk
 
 		# check if any errors occurred in input writing, or if ffmpeg exited non-success.
 		if ffmpeg.wait() != 0:
 			raise Exception("Error while streaming cut: ffmpeg exited {}".format(ffmpeg.returncode))
+		input_feeder.get() # re-raise any errors from feed_input()
 
-		# Now actually yield the resulting file
+		# When not streaming, we can only return the data once ffmpeg has exited
+		if not stream:
 			for chunk in read_chunks(tempfile):
 				yield chunk
 	finally:
 		# if something goes wrong, try to clean up ignoring errors
+		if input_feeder is not None:
+			input_feeder.kill()
 		if ffmpeg is not None and ffmpeg.poll() is None:
 			for action in (ffmpeg.kill, ffmpeg.stdin.close, ffmpeg.stdout.close):
 				try:

cutter/cutter/main.py

@@ -294,8 +294,14 @@ class Cutter(object):
 			self.logger.debug("No encoding settings, using fast cut")
 			cut = fast_cut_segments(job.segments, job.video_start, job.video_end)
 		else:
-			self.logger.debug("Using encoding settings for cut: {}".format(upload_backend.encoding_settings))
-			cut = full_cut_segments(job.segments, job.video_start, job.video_end, upload_backend.encoding_settings)
+			self.logger.debug("Using encoding settings for {} cut: {}".format(
+				"streamable" if upload_backend.encoding_streamable else "non-streamable",
+				upload_backend.encoding_settings,
+			))
+			cut = full_cut_segments(
+				job.segments, job.video_start, job.video_end,
+				upload_backend.encoding_settings, stream=upload_backend.encoding_streamable,
+			)
 
 		# This flag tracks whether we've told requests to finalize the upload,
 		# and serves to detect whether errors from the request call are recoverable.

cutter/cutter/upload_backends.py

@@ -67,12 +67,17 @@ class UploadBackend(object):
 	under the 'encoding_settings' attribute.
 	If this is None, instead uses the 'fast cut' strategy where nothing
 	is transcoded.
+
+	In addition, if the output format doesn't need a seekable file,
+	you should set encoding_streamable = True so we know we can stream the output directly.
 	"""
 
 	needs_transcode = False
 
-	# reasonable default if settings don't otherwise matter
-	encoding_settings = ['-f', 'mp4']
+	# reasonable default if settings don't otherwise matter:
+	# high-quality mpegts, without wasting too much cpu on encoding
+	encoding_args = ['-c:v', 'libx264', '-preset', 'ultrafast', '-crf', '0', '-f', 'mpegts']
+	encoding_streamable = True
 
 	def upload_video(self, title, description, tags, data):
 		raise NotImplementedError
@@ -92,10 +97,14 @@ class Youtube(UploadBackend):
 		language:
 			The language code to describe all videos as.
 			Default is "en", ie. English. Set to null to not set.
+		use_yt_recommended_encoding:
+			Default False. If True, use the ffmpeg settings that Youtube recommends for
+			fast processing once uploaded. We suggest not bothering, as it doesn't appear
+			to make much difference.
 	"""
 
 	needs_transcode = True
-	encoding_settings = [
+	recommended_settings = [
 		# Youtube's recommended settings:
 		'-codec:v', 'libx264', # Make the video codec x264
 		'-crf', '21', # Set the video quality, this produces the bitrate range that YT likes
@@ -108,7 +117,7 @@ class Youtube(UploadBackend):
 		'-movflags', 'faststart', # put MOOV atom at the front of the file, as requested
 	]
 
-	def __init__(self, credentials, hidden=False, category_id=23, language="en"):
+	def __init__(self, credentials, hidden=False, category_id=23, language="en", use_yt_recommended_encoding=False):
 		self.logger = logging.getLogger(type(self).__name__)
 		self.client = GoogleAPIClient(
 			credentials['client_id'],
@@ -118,6 +127,9 @@ class Youtube(UploadBackend):
 		self.hidden = hidden
 		self.category_id = category_id
 		self.language = language
+		if use_yt_recommended_encoding:
+			self.encoding_settings = self.recommended_settings
+			self.encoding_streamable = False
 
 	def upload_video(self, title, description, tags, data):
 		json = {

restreamer/restreamer/main.py

@@ -237,7 +237,6 @@ def cut(channel, quality):
 			Even if holes are allowed, a 406 may result if the resulting video would be empty.
 		type: One of "fast" or "full". Default to "fast".
 			A fast cut is much faster but minor artifacting may be present near the start and end.
-			A fast cut is encoded as MPEG-TS, a full as mp4.
 	"""
 	start = dateutil.parse_utc_only(request.args['start']) if 'start' in request.args else None
 	end = dateutil.parse_utc_only(request.args['end']) if 'end' in request.args else None
@@ -272,8 +271,9 @@ def cut(channel, quality):
 	if type == 'fast':
 		return Response(fast_cut_segments(segments, start, end), mimetype='video/MP2T')
 	elif type == 'full':
-		# output as mp4 with no more specific encoding args
-		return Response(full_cut_segments(segments, start, end, ['-f', 'mp4']), mimetype='video/mp4')
+		# output as high-quality mpegts, without wasting too much cpu on encoding
+		encoding_args = ['-c:v', 'libx264', '-preset', 'ultrafast', '-crf', '0', '-f', 'mpegts']
+		return Response(full_cut_segments(segments, start, end, encoding_args, stream=True), mimetype='video/MP2T')
 	else:
 		return "Unknown type {!r}. Must be 'fast' or 'full'.".format(type), 400