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Adjust frag_duration setting in stream (#59135)

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uvjustin 2021-11-06 09:54:51 +08:00 • committed by GitHub
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18
homeassistant/components/stream/worker.py
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@ -102,18 +102,18 @@ class SegmentBuffer:
# 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
# have variability in their durations and can end up being too short or too long. 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.
# If there are two tracks, as in the case of a video feed with audio, there is an added
# wrinkle as the fragment cut seems to be done on the first track that crosses the desired
# threshold, and cutting on the audio track may also result in a shorter video fragment
# than desired.
# Given this, our approach is to give ffmpeg a frag_duration somewhere in the middle
# of the range, hoping that the parts stay pretty well bounded, and we adjust the part
# durations a bit in the hls metadata so that everything "looks" ok.
"frag_duration": str(
self._stream_settings.part_target_duration
* (98e4 if add_audio else 9e5)
self._stream_settings.part_target_duration * 9e5
),
}
if self._stream_settings.ll_hls