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Deal with unexpected or missing SoundCheck values

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* Deals with gain values of 0 in SoundCheck files by interpreting them
  as 0.0dB rather than causing an exception
* Return default values if SoundCheck tag is malformed in some way
* Other misc changes for compactness
This commit is contained in:
Dave Hayes 2013-02-07 08:46:27 -06:00
parent 8a3221abd2
commit 93d1b646f4
1 changed files with 15 additions and 13 deletions
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28
beets/mediafile.py
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@ -186,23 +186,25 @@ def _pack_asf_image(mime, data, type=3, description=""):
def _sc2rg(soundcheck):
"""Convert a SoundCheck tag to ReplayGain values"""
# SoundCheck tags consist 10 numbers, each represented by 8 characters
# SoundCheck tags consist of 10 numbers, each represented by 8 characters
# of ASCII hex preceded by a space.
soundcheck = soundcheck.replace(' ', '')
soundcheck = struct.unpack('!iiiiiiiiii', soundcheck.decode('hex'))
try:
soundcheck = soundcheck.replace(' ', '').decode('hex')
soundcheck = struct.unpack('!iiiiiiiiii', soundcheck)
except:
# SoundCheck isn't in the format we expect, so return default values
return 0.0, 0.0
# SoundCheck stores absolute calculated/measured RMS value in an unknown
# unit. We need to find the ratio of this measurement compared to a
# reference value of 1000 to get our gain in dB.
left = math.log10(soundcheck[0] / 1000.0) * -10
right = math.log10(soundcheck[1] / 1000.0) * -10
# We play it safe by using the smallest value (i.e., largest reduction)
gain = round(min(left, right), 2)
# reference value of 1000 to get our gain in dB. We play it safe by using
# the larger of the two values (i.e., the most attenuation).
gain = math.log10((max(*soundcheck[:2]) or 1000) / 1000.0) * -10
# SoundCheck stores peak values as the actual value of the sample, and
# again separately for the left and right channels. We need to convert
# this to a percentage of full scale, which is 32768 for a 16 bit sample.
# Once again, we play it safe by using the larger of the two values.
peak = round(max(soundcheck[6], soundcheck[7]) / 32768.0, 6)
return (gain, peak)
peak = max(soundcheck[6:8]) / 32768.0
return round(gain, 2), round(peak, 6)
def _rg2sc(gain, peak):
@ -221,10 +223,10 @@ def _rg2sc(gain, peak):
# Same as above, except our reference level is 2500 units.
g2 = min(round((10 ** (gain / -10)) * 2500), 65534)
# The purpose of these values are unknown, but they also seem to be
# unused so we just pick a sensible number.
uk = 150696
# unused so we just use 0
uk = 0
values = (g1, g1, g2, g2, uk, uk, peak, peak, uk, uk)
soundcheck = (' %08X' * 10) % values
soundcheck = (u' %08X' * 10) % values
return soundcheck
# Flags for encoding field behavior.