[Flac-dev] metaflac: New tags to replace crossfading in players.

[Tim Phipps]

Hi All,
	I'd like to improve the way MPD (and other players) switches between tracks. 
I'd like something like crossfade but without any fading. I'd like the player 
to just overlap the end of one track with the beginning of the next track to 
provide a nice transition. Crossfading in MPD doesn't work for me since it 
just ramps the volume up/down over a fixed time and some tracks just don't 
suit this e.g. tracks that fade in/out already and tracks that start/stop 
with bangs.

I'd like to use the replaygain code in metaflac to also record the volume 
profiles at the start and end of the track and then use those profiles in the 
player to work out how much to overlap two tracks by. To do it in one pass 
will mean recording the non-replaygain volumes and the the player will have 
to factor in whatever replaygain it's going to use. The player can then have 
a crossover level set (probably a config setting) and it would calculate the 
times at which the start and end profiles crossed that level and schedule the 
crossover accordingly. I think this means storing a set of volumes and times 
in the tags so the player can do some interpolations and so you don't have to 
rerun metaflac if you change your chosen crossover level or replaygain 
settings.

What should these tags look like? Should I have tags like:

START_90dB=0.000s
START_80dB=0.567s
START_70dB=2.557s
START_60dB=4.676s
...
END_80db=200.678s
END_90db=201.034s

or something like:

START_PROFILE="90=0.001,80=0.576,70=2.557,60=4.676"
END_PROFILE="80=200.678,90=210.034"

I don't know what the dB intervals should be or what the range should be. I'm 
guessing that anything less than 60db won't matter even though I typed in 
90dB above. Any suggestions would be welcome and any help in coding and/or 
testing would be good.

Cheers,
Tim.