TO DO: Implementation of Speed 1 and Speed 2
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Autoscroll currently using the speed automatically determined by the lyrics length
However if the song is not full version and the lyrics is, it will be too fast.
The speed shall be as similar as the normal song.
The speed conversion shall be introduced when the user click / switch the speed
the current position (progress) will be recorded as w0 (m0) and position will be changed into
pos_w = rate * pos_m + y0
rate(0) = 1
y0(0) = 0
After having the w0 (or m0),
w0(n) = rate(n) * m0(n) + y0(n)
rate(1) = new rate
rate(0) * m0 + y0(0) = rate(1) * m0 + y0(1)
y0(1) = y0(0) + ( rate(0) - rate(1) ) * m0
Speed 1: automatic
Speed 2: the specified rate according to correct songs, such as
https://www.youtube.com/watch?v=sXrkgyxATwg
The speed control will be entirely by the script inside iframe, including cubicBezier
This shall be moved into the library.
The external script will only provide the pos_m and let the library to do pos_w conversion.
Closed due to no time. Just ignore this feature first.