I mentioned this bug in MinG's Aspire map thread, but as I never heard anyone mentioning anything like this and didn't found it on list of known issues, I decided to report it.
Only similar thing I found is this few years old thread, but it looks to be not valid anymore, because in comparison to that thread, how it works right now is completely different thing: not just sprite change without speed changing, but the speed is truly changed to faster or slower one; Changing speeds doesn't fix anything; Also, you don't need to have any "ninja reflexes" for that, you can just prevent map from starting with pointing cursor on "visual Settings" window, how I did in the video, then change it casually.
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So, going to the point:
If you watch a replay, be it from other players or with Auto, then change Playback speed with [F] key at the very beginning, then the chosen setting will be used as a base speed setting and changing speed will be applied to it, resulting in ability to reduce or increase it excessively.
Normally, 1x is a "base speed", so changing it to 2x will multiply the speed by 2, while changing it to 0.5x will multiply speed by 0.5.
But, if at the very beginning of the map, you will change the speed to 2x, then the song will be played at 100% speed, but this 2x setting will be your "base speed".
Because 2x is 2 times more than 1x, then changing speed to 1x will result in song being played at half of speed (0.5x real speed). Setting it to 0.5x makes it even slower, I guess it's 1/4-th of the speed? (0.25x real speed).
You can also change Playback speed at the beginning to 0.5x and it will be used as 100% speed too. Because 1x and 2x are double the previous speeds, then they will consecutively make the speed faster being 2x and... 3x?? At first I thought that it's 4x, but it sounds very similar to 2x DT playback, which is 3x.
I suppose that this is not just multiplying speed, but switching to one of the fixed speeds that are available? Or something else?
In similar matter, you can also use HT, which is x0.75 speed multiplier and normally gives you playback speeds (on 0.5x, 1x, 2x settings) like: (0.375x, 0.75x, 1.5x). After modifying, the speeds will change, if what I am saying is correct that the new speeds will be:
2x --> (0.1875 ??? (a guess, can be something else) , 0.375x, 0.75x)
0.5x --> (0.75x, 1x ???, 1.5x ???) (looks like this combination roughly gives you speeds equivalent of normal and DT speed)
Similar with DT, which is x1.5 multiplier and should give playback speeds (0.75x, 1.5x, 3x), will get modified to
0.5x --> (1.5x, 3x , 6x)
2x --> (0.5x ? , 1x ? , 1.5x )
Even with modifying speed like this, spinners looks to get similar bonus, but the animation speed changes and similar "real" speeds can give auto visually spinning differently. I didn't excessively tested everything, but it should be very easy to reproduce, both on Stable and CuttingEdge (I didn't tested Beta and Fallback (changing to fallback always crashes my database xd)
Video or screenshot showing the problem (only NoMod, easy to do the same with HT (to get very slow speed) and DT (it roughly looks like double the speed of DT on 2x, so it's 6x)
https://www.youtube.com/watch?v=pQIYga1P9RU
osu! version: 20170404cuttingedge, current stable too
Edit:
Looks like bug can be joined with 6-9 speed modifying CE keys. By setting base DT replay steep to 2x, then reducing it to 0.5x and clicking [7] you can get a song being played (I think) at normal speed, but with chipmunk modified voice, haha xD
My uploading speed is very slow, but I will try to record and upload something
Edit 2:
https://www.youtube.com/watch?v=X2qfR01Ry4E
I set DT base speed to 2x, then changed setting to 0.5x and used CE [7] key, to apply speed increase. This way I have "chimpunk voices" on... I think it's normal song speed?
Only similar thing I found is this few years old thread, but it looks to be not valid anymore, because in comparison to that thread, how it works right now is completely different thing: not just sprite change without speed changing, but the speed is truly changed to faster or slower one; Changing speeds doesn't fix anything; Also, you don't need to have any "ninja reflexes" for that, you can just prevent map from starting with pointing cursor on "visual Settings" window, how I did in the video, then change it casually.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
So, going to the point:
If you watch a replay, be it from other players or with Auto, then change Playback speed with [F] key at the very beginning, then the chosen setting will be used as a base speed setting and changing speed will be applied to it, resulting in ability to reduce or increase it excessively.
Normally, 1x is a "base speed", so changing it to 2x will multiply the speed by 2, while changing it to 0.5x will multiply speed by 0.5.
But, if at the very beginning of the map, you will change the speed to 2x, then the song will be played at 100% speed, but this 2x setting will be your "base speed".
Because 2x is 2 times more than 1x, then changing speed to 1x will result in song being played at half of speed (0.5x real speed). Setting it to 0.5x makes it even slower, I guess it's 1/4-th of the speed? (0.25x real speed).
You can also change Playback speed at the beginning to 0.5x and it will be used as 100% speed too. Because 1x and 2x are double the previous speeds, then they will consecutively make the speed faster being 2x and... 3x?? At first I thought that it's 4x, but it sounds very similar to 2x DT playback, which is 3x.
I suppose that this is not just multiplying speed, but switching to one of the fixed speeds that are available? Or something else?
In similar matter, you can also use HT, which is x0.75 speed multiplier and normally gives you playback speeds (on 0.5x, 1x, 2x settings) like: (0.375x, 0.75x, 1.5x). After modifying, the speeds will change, if what I am saying is correct that the new speeds will be:
2x --> (0.1875 ??? (a guess, can be something else) , 0.375x, 0.75x)
0.5x --> (0.75x, 1x ???, 1.5x ???) (looks like this combination roughly gives you speeds equivalent of normal and DT speed)
Similar with DT, which is x1.5 multiplier and should give playback speeds (0.75x, 1.5x, 3x), will get modified to
0.5x --> (1.5x, 3x , 6x)
2x --> (0.5x ? , 1x ? , 1.5x )
Even with modifying speed like this, spinners looks to get similar bonus, but the animation speed changes and similar "real" speeds can give auto visually spinning differently. I didn't excessively tested everything, but it should be very easy to reproduce, both on Stable and CuttingEdge (I didn't tested Beta and Fallback (changing to fallback always crashes my database xd)
Video or screenshot showing the problem (only NoMod, easy to do the same with HT (to get very slow speed) and DT (it roughly looks like double the speed of DT on 2x, so it's 6x)
https://www.youtube.com/watch?v=pQIYga1P9RU
osu! version: 20170404cuttingedge, current stable too
Edit:
Looks like bug can be joined with 6-9 speed modifying CE keys. By setting base DT replay steep to 2x, then reducing it to 0.5x and clicking [7] you can get a song being played (I think) at normal speed, but with chipmunk modified voice, haha xD
My uploading speed is very slow, but I will try to record and upload something
Edit 2:
https://www.youtube.com/watch?v=X2qfR01Ry4E
I set DT base speed to 2x, then changed setting to 0.5x and used CE [7] key, to apply speed increase. This way I have "chimpunk voices" on... I think it's normal song speed?
