Implement Beat jumping mode

[jus]

Beat Jumping allows you to jump forwards or backwards within the track.

As requested http://www.mixxx.org/forums/viewtopic.php?f=6&t=3209
<quote>
Virtual DJ has this feature and I used it every single night. You can define a number of beats and jump back that many automatically. I would use this all the time when songs had irregular chorusses or if I wanted to loop a section but I missed the start.
</quote>

It should have:
* A control to choose a jump size ( by 1/32 -32 beats, just like for beat loops)
* A control to jump forwards or backwards by the selected jump size.

[allen bina (allenbina)]

This could also be considered looping if the time where you set the loop is at the end position of the loop.

[icarusrj (icarusrj)]

Guys, as a Virtual DJ user, beat jumping is a feature that I use every single night!
That helps a lot for example, when you want to mix the end of a singing with the start of a singing in another song. (Sorry my poor english lol).
I hope you guys understand and please please please put this feature on MIXXX!
Once you do it, I will be the most MIXXX propagandist!
Thank you!

[Daniel Schürmann (daschuer)]

connected to Bug #990976

[xorik (xor29a)]

I think we can use loop's buttons for the beatjump, and just add switch or button to change behavior, like this:
http://img35.imageshack.us/img35/3724/kqx.png

After pressing it, loop size will be jump size, begin of loop will be jump backward end of loop will be jump forward. Loop button isn't need it the beatjump mode.

[Owen Williams (ywwg)]

It would also be handy to adjust beats while not looping -- for those occasions when a DJ messes up a transition and gets one beat off.

[RJ Skerry-Ryan (rryan)]

Adding:

[ChannelX],beatjump
[ChannelX],beatjump_%1_forward
[ChannelX],beatjump_%1_backward

These are completely analogous to beatloops and simply seek forward or backward by the multiple of the beat length. The sizes available are the same as those available for beatloops.

Setting beatjump directly (positive for forward, negative for backward) allows jumping by an arbitrary fraction.

[Daniel Schürmann (daschuer)]

How is ensured that the samples you jump to are in cache?

[Owen Williams (ywwg)]

As the Release Dictator, I think this is a feature and shouldn't go in. As a DJ using Mixxx, I really, really want this feature so I'll let it go :P.

I'm going to tag this "bullet-point", along with other features we've implemented that I think should be explicitly mentioned on the website when this version is released.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/6221