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replaygain: in ffmpeg backend refactor album gain calculation

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now that we have the `track_results` upfront, some simplifications are
possible
This commit is contained in:
wisp3rwind 2022-02-01 21:55:29 +01:00
parent 76f6c86291
commit fa37085493
1 changed files with 18 additions and 19 deletions
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37
beetsplug/replaygain.py
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@ -321,35 +321,33 @@ class FfmpegBackend(Backend):
# list of track Gain objects
track_gains = [tg for tg, _nb in track_results]
# maximum peak
album_peak = 0
# sum of BS.1770 gating block powers
sum_powers = 0
# total number of BS.1770 gating blocks
n_blocks = 0
# Album peak is maximum track peak
album_peak = max(tg.peak for tg in track_gains)
for (track_gain, track_n_blocks) in track_results:
# album peak is maximum track peak
album_peak = max(album_peak, track_gain.peak)
# prepare album_gain calculation
# total number of blocks is sum of track blocks
n_blocks += track_n_blocks
# Total number of BS.1770 gating blocks
n_blocks = sum(nb for _tg, nb in track_results)
def sum_of_track_powers(track_gain, track_n_blocks):
# convert `LU to target_level` -> LUFS
track_loudness = target_level_lufs - track_gain.gain
loudness = target_level_lufs - track_gain
# This reverses ITU-R BS.1770-4 p. 6 equation (5) to convert
# from loudness to power. The result is the average gating
# block power.
track_power = 10**((track_loudness + 0.691) / 10)
power = 10**((loudness + 0.691) / 10)
# Weight that average power by the number of gating blocks to
# get the sum of all their powers. Add that to the sum of all
# block powers in this album.
sum_powers += track_power * track_n_blocks
# Multiply that average power by the number of gating blocks to get
# the sum of all block powers in this track.
return track_n_blocks * power
# calculate album gain
if n_blocks > 0:
# Sum over all tracks to get the sum of BS.1770 gating block powers
# for the entire album.
sum_powers = sum(
sum_of_track_powers(tg, nb) for tg, nb in track_results
)
# compare ITU-R BS.1770-4 p. 6 equation (5)
# Album gain is the replaygain of the concatenation of all tracks.
album_gain = -0.691 + 10 * math.log10(sum_powers / n_blocks)
@ -365,6 +363,7 @@ class FfmpegBackend(Backend):
task.album_gain = Gain(album_gain, album_peak)
task.track_gains = track_gains
return task
def _construct_cmd(self, item, peak_method):