Original keys

[Andy Mopley]

I am finding that often a piece of classical music from YouTube is either 1/2 step up or down from the original key it was written in. Is this because:
a) the piece isn't always performed in the original key (which makes me wonder why??)
b) there is something that happens in the process which impacts the key, up or down
c) I need to check my hearing

Any thoughts?

Thanks for reading

[neilG]

If it's always 1/2 step, it's either bad playback of ancient technology like vinyl and tape, or the use of so-called historical tuning. An A=415 Baroque tuning will sound exactly 1/2 step below A=440.
A whole step in a piece for bass would be the use of orchestra tuning in place of solo tuning or vice versa. There's also 1/2 tuning in Viennese tuning.
Other than that, yeah, get your hearing checked.