Something I realized fairly early on while building KaraokeBot was that the "Karaoke Version" of a given song can deviate a lot from the original.
The most common alteration made is to the "key" of the song.
The companies putting out karaoke versions seem to think that lowering a song's pitch will render it more "singable" (by a human).
They might be right, but this meant that my synthesized vocals had to be shifted around to match what was available at my local Karaoke Bar.
Another common change is that of BPM (beats per minute; the song's tempo).
For example, Daft Punk's "Digital Love" comes in at around 124.662 BPM, but most Google search results (and Karaoke Bars) are happy to round up to 125.
Since my bot's vocals needed to match the corresponding karaoke versions' BPM precisely (lest the two disgracefully desync), I actually ended up making two trips to VENUS Karaoke in the International District - once to rip direct feed audio of a few of their songs (to later analyze in FL Studio and determine their absolute BPMs), and then again to record video/audio of KaraokeBot doing it's thing.
In the end, I think it was worth it :-)
(PS: here's a little snippet of KaraokeBot's Digital Love cover)