feature: option to automatically enable keylock for beatmapped tracks

[Owen Williams]

When mixing beatmapped tracks, especially with master sync, Mixxx might have to adjust the playback speed of the beatmapped track to maintain sync. This can cause audio pitch artifacts that may be undesirable. It might be nice to add an option to always enable keylock when a beatmapped track is loaded and master sync is enabled for that deck.

[Owen Williams (ywwg)]

There is a decent argument to be made here that mixxx shouldn't try to do this kind of intelligent thing -- an argument I've made myself :). But I'd be interested to know if anyone else thinks this would be useful.

[Daniel Schürmann (daschuer)]

I think this is probably too much magic.
There might be many edge cases related to cpu performance and personal preferences.

I think the underlying issue is that we actually don't want to change the track tempo at all during the transition.

If we look at Auto DJ where the transition time is known, we may calculate the optimum const speed forehead. This will lead into some intermediate beats off, but I guess that sounds much better than constantly tweaking the pitch.

[ronso0 (ronso0)]

I think toggling keylock automatically is too much; as daschuer pointed out this might cause conseqences a user wanted to avoid by disabling keylock.

Calculating a proper average transition speed for AutoDJ seems like a good solution.

For manual mixing it might help to have some kind of marker in the BPM display that tells us when the track's BPM is not constant, so the user is aware he/she needs to pay attention when mixing such tracks, with or without Sync enabled.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/9821