Quote:
Originally Posted by sneaker_ger
There are different things. The "actual" adjustment is made in each frame in "global_gain" element (MediaInfo shows this). Then mp3gain may also add APEv2 tags to undo adjustment or make it more precise (global_gain is 1.5 dB steps).
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Which is why I originally said it's possible to losslessly adjust the volume of MP3s.... unless there's some other definition of "losslessly adjusting the volume" to which changing the global_gain of each frame wouldn't apply?
There's no law stating the global_gain value for each frame must be adjusted by the same amount, which is why MP3DirectCut can change the volume of specific parts of an MP3 or apply fade-ins and fade-outs etc.
Quote:
Originally Posted by sneaker_ger
There is no reserved space for either global_gain or APEv2. global_gain is always present in every mp3 file. Just needs to be altered. The (optional) APEv2 tag will be added.
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I realise MP3Gain adds ReplayGain/undo information to an APEv2 tag, but I didn't say the field was used for either global gain or APEv2 or that it's ever used at all. Only that it exists.
Is there also some other definition of "logging a volume adjustment" that'd only apply in this case?
http://gabriel.mp3-tech.org/mp3infotag.html
byte $B5 MP3 Gain
any mp3 can be amplified by a factor 2 ^ ( x * 0.25) in a lossless manner by a tool like eg. mp3gain
byte $B5 is set to (00)h by default.
if done so, this 8-bit field can be used to log such transformation happened so that any given time it can be undone.
I still don't know which volume flag Asmodian referred to. Was there a time MP3 players ignored the global_gain of each frame? It sounded to me like he was referring to some sort of "master volume" flag, but aside from the possibility of using the ReplayGain field in the MP3 header, which is far as I know isn't widely supported by players, I don't know what field/flag that'd be.