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Improve part metadata in stream (#58822)

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uvjustin 2021-11-01 11:23:01 +08:00 • committed by GitHub
parent 7126c9b0de
commit 9aaa92f366
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2 changed files with 106 additions and 63 deletions
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117
homeassistant/components/stream/worker.py
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@ -66,9 +66,15 @@ class SegmentBuffer:
memory_file: BytesIO,
sequence: int,
input_vstream: av.video.VideoStream,
) -> av.container.OutputContainer:
"""Make a new av OutputContainer."""
return av.open(
input_astream: av.audio.stream.AudioStream,
) -> tuple[
av.container.OutputContainer,
av.video.VideoStream,
av.audio.stream.AudioStream | None,
]:
"""Make a new av OutputContainer and add output streams."""
add_audio = input_astream and input_astream.name in AUDIO_CODECS
container = av.open(
memory_file,
mode="w",
format=SEGMENT_CONTAINER_FORMAT,
@ -93,19 +99,21 @@ class SegmentBuffer:
# Create a fragment every TARGET_PART_DURATION. The data from each fragment is stored in
# a "Part" that can be combined with the data from all the other "Part"s, plus an init
# section, to reconstitute the data in a "Segment".
# frag_duration is the threshold for determining part boundaries, and the dts of the last
# packet in the part should correspond to a duration that is smaller than this value.
# However, as the part duration includes the duration of the last frame, the part duration
# will be equal to or greater than this value.
# We previously scaled this number down by .85 to account for this while keeping within
# the 15% variance allowed in part duration. However, this did not work when inputs had
# an audio stream - sometimes the fragment would get cut on the audio packet, causing
# the durations to actually be to short.
# The current approach is to use this frag_duration for creating the media while
# adjusting the metadata duration to keep the durations in the metadata below the
# part_target_duration threshold.
# The LL-HLS spec allows for a fragment's duration to be within the range [0.85x,1.0x]
# of the part target duration. We use the frag_duration option to tell ffmpeg to try to
# cut the fragments when they reach frag_duration. However, the resulting fragments can
# have variability in their durations and can end up being too short or too long. If
# there are two tracks, as in the case of a video feed with audio, the fragment cut seems
# to be done on the first track that crosses the desired threshold, and cutting on the
# audio track may result in a shorter video fragment than desired. Conversely, with a
# video track with no audio, the discrete nature of frames means that the frame at the
# end of a fragment will sometimes extend slightly beyond the desired frag_duration.
# Given this, our approach is to use a frag_duration near the upper end of the range for
# outputs with audio using a frag_duration at the lower end of the range for outputs with
# only video.
"frag_duration": str(
self._stream_settings.part_target_duration * 1e6
self._stream_settings.part_target_duration
* (98e4 if add_audio else 9e5)
),
}
if self._stream_settings.ll_hls
@ -113,6 +121,12 @@ class SegmentBuffer:
),
},
)
output_vstream = container.add_stream(template=input_vstream)
# Check if audio is requested
output_astream = None
if add_audio:
output_astream = container.add_stream(template=input_astream)
return container, output_vstream, output_astream
def set_streams(
self,
@ -128,26 +142,22 @@ class SegmentBuffer:
"""Initialize a new stream segment."""
# Keep track of the number of segments we've processed
self._sequence += 1
self._segment_start_dts = video_dts
self._part_start_dts = self._segment_start_dts = video_dts
self._segment = None
self._memory_file = BytesIO()
self._memory_file_pos = 0
self._av_output = self.make_new_av(
(
self._av_output,
self._output_video_stream,
self._output_audio_stream,
) = self.make_new_av(
memory_file=self._memory_file,
sequence=self._sequence,
input_vstream=self._input_video_stream,
)
self._output_video_stream = self._av_output.add_stream(
template=self._input_video_stream
input_astream=self._input_audio_stream,
)
if self._output_video_stream.name == "hevc":
self._output_video_stream.codec_tag = "hvc1"
# Check if audio is requested
self._output_audio_stream = None
if self._input_audio_stream and self._input_audio_stream.name in AUDIO_CODECS:
self._output_audio_stream = self._av_output.add_stream(
template=self._input_audio_stream
)
def mux_packet(self, packet: av.Packet) -> None:
"""Mux a packet to the appropriate output stream."""
@ -186,13 +196,9 @@ class SegmentBuffer:
# Fetch the latest StreamOutputs, which may have changed since the
# worker started.
stream_outputs=self._outputs_callback().values(),
start_time=self._start_time
+ datetime.timedelta(
seconds=float(self._segment_start_dts * packet.time_base)
),
start_time=self._start_time,
)
self._memory_file_pos = self._memory_file.tell()
self._part_start_dts = self._segment_start_dts
else: # These are the ends of the part segments
self.flush(packet, last_part=False)
@ -201,17 +207,23 @@ class SegmentBuffer:
If last_part is True, also close the segment, give it a duration,
and clean up the av_output and memory_file.
There are two different ways to enter this function, and when
last_part is True, packet has not yet been muxed, while when
last_part is False, the packet has already been muxed. However,
in both cases, packet is the next packet and is not included in
the Part.
This function writes the duration metadata for the Part and
for the Segment. However, as the fragmentation done by ffmpeg
may result in fragment durations which fall outside the
[0.85x,1.0x] tolerance band allowed by LL-HLS, we need to fudge
some durations a bit by reporting them as being within that
range.
Note that repeated adjustments may cause drift between the part
durations in the metadata and those in the media and result in
playback issues in some clients.
"""
# In some cases using the current packet's dts (which is the start
# dts of the next part) to calculate the part duration will result in a
# value which exceeds the part_target_duration. This can muck up the
# duration of both this part and the next part. An easy fix is to just
# use the current packet dts and cap it by the part target duration.
# The adjustment may cause a drift between this adjusted duration
# (used in the metadata) and the media duration, but the drift should be
# automatically corrected when the part duration cleanly divides the
# framerate.
current_dts = min(
# Part durations should not exceed the part target duration
adjusted_dts = min(
packet.dts,
self._part_start_dts
+ self._stream_settings.part_target_duration / packet.time_base,
@ -220,29 +232,44 @@ class SegmentBuffer:
# Closing the av_output will write the remaining buffered data to the
# memory_file as a new moof/mdat.
self._av_output.close()
elif not self._part_has_keyframe:
# Parts which are not the last part or an independent part should
# not have durations below 0.85 of the part target duration.
adjusted_dts = max(
adjusted_dts,
self._part_start_dts
+ 0.85 * self._stream_settings.part_target_duration / packet.time_base,
)
assert self._segment
self._memory_file.seek(self._memory_file_pos)
self._hass.loop.call_soon_threadsafe(
self._segment.async_add_part,
Part(
duration=float((current_dts - self._part_start_dts) * packet.time_base),
duration=float(
(adjusted_dts - self._part_start_dts) * packet.time_base
),
has_keyframe=self._part_has_keyframe,
data=self._memory_file.read(),
),
float((current_dts - self._segment_start_dts) * packet.time_base)
(
segment_duration := float(
(adjusted_dts - self._segment_start_dts) * packet.time_base
)
)
if last_part
else 0,
)
if last_part:
# If we've written the last part, we can close the memory_file.
self._memory_file.close() # We don't need the BytesIO object anymore
self._start_time += datetime.timedelta(seconds=segment_duration)
# Reinitialize
self.reset(current_dts)
self.reset(packet.dts)
else:
# For the last part, these will get set again elsewhere so we can skip
# setting them here.
self._memory_file_pos = self._memory_file.tell()
self._part_start_dts = current_dts
self._part_start_dts = adjusted_dts
self._part_has_keyframe = False
def discontinuity(self) -> None: