Same as track_gain, but for the whole album.
Same as track_peak, but for the whole album,
Track replay gain in microbels (divide by 100000 to get the value in dB). Should be set to INT32_MIN when unknown.
Peak track amplitude, with 100000 representing full scale (but values may overflow). 0 when unknown.
ReplayGain information (see http://wiki.hydrogenaudio.org/index.php?title=ReplayGain_1.0_specification). The size of this struct is a part of the public ABI.