91 lines
3.2 KiB
Python
91 lines
3.2 KiB
Python
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"""Skip silence in the browser: the pauses of an episode, found once on the server.
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Android's player skips silence itself. A browser can't listen to the audio of
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most podcast servers (no CORS: Web Audio hears only zeros), so the server
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reads the file once with ffmpeg's silencedetect and keeps the pauses on the
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episode (PodcastEpisode.silences); the browser then jumps over them while it
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plays (podcasts-web.js).
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"""
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import logging
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import re
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import subprocess
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import threading
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from django.db import close_old_connections
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log = logging.getLogger(__name__)
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NOISE = '-35dB' # quieter than this counts as silence
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MIN_SILENCE = 0.4 # seconds; shorter pauses stay (they belong to speech)
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TIMEOUT = 900 # seconds for one episode (download and decode)
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MAX_RUNNING = 2 # episodes analysed at the same time
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_START = re.compile(r'silence_start: (-?[\d.]+)')
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_END = re.compile(r'silence_end: ([\d.]+)')
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_running = set()
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_lock = threading.Lock()
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_slots = threading.BoundedSemaphore(MAX_RUNNING)
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def parse(stderr):
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"""ffmpeg's silencedetect output -> [[start, end], …] in seconds (2 decimals)."""
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spans = []
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start = None
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for line in stderr.splitlines():
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m = _START.search(line)
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if m:
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start = max(0.0, float(m.group(1)))
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continue
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m = _END.search(line)
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if m and start is not None:
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end = float(m.group(1))
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if end - start >= MIN_SILENCE:
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spans.append([round(start, 2), round(end, 2)])
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start = None
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return spans
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def analyze(url):
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"""The pauses of the audio at `url` (ffmpeg reads it straight from there)."""
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import imageio_ffmpeg
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proc = subprocess.run(
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[imageio_ffmpeg.get_ffmpeg_exe(), '-nostdin', '-hide_banner', '-nostats',
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'-user_agent', 'diora podcast silence', '-vn', '-sn', '-dn', '-i', url,
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'-af', f'silencedetect=noise={NOISE}:d={MIN_SILENCE}', '-f', 'null', '-'],
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capture_output=True, text=True, timeout=TIMEOUT,
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)
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if proc.returncode != 0:
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tail = (proc.stderr or '').strip().splitlines()[-1:] or ['ffmpeg failed']
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raise RuntimeError(tail[0][:200])
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return parse(proc.stderr)
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def ensure(episode_id):
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"""Find the episode's pauses in the background, unless that runs already."""
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with _lock:
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if episode_id in _running:
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return
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_running.add(episode_id)
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threading.Thread(target=_work, args=(episode_id,), daemon=True).start()
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def _work(episode_id):
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from .models import PodcastEpisode
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try:
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with _slots:
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close_old_connections()
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ep = PodcastEpisode.objects.filter(pk=episode_id).only('id', 'audio_url').first()
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if ep is None:
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return
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try:
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result = {'spans': analyze(ep.audio_url)}
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except Exception as e: # unreachable file, timeout, not audio: remembered, not retried
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log.warning('silences of episode %s failed: %s', episode_id, e)
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result = {'spans': [], 'error': str(e)[:200] or type(e).__name__}
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PodcastEpisode.objects.filter(pk=episode_id).update(silences=result)
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finally:
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with _lock:
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_running.discard(episode_id)
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close_old_connections()
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