How do I extract a time reference from a long track with many tempo changes?

Hi,

this is a question about a typical audio special ops that is needed when you record live tracks and would like to add some audio events to that recording after the fact. This can also happen to video recordings, where you might have multiple audio tracks and still would like to add some more audio.

So basically I have one long audio track as reference with some live music that has lots of variations in time - not only are the musicians very creative in their usage of time, also they make extensive use of accelerandos and ritardandos, so the time changes constantly.

I know this is a special challenge for every audio engineer, so I do not expect a silver bullet, however I would like to ask, how to master such a task with ardour? Are there any special tools / plugins available that might help? How would you do it?

Several approaches come to mind, e.g. cut the reference track into many pieces where a tempo can be clearly applied to, then insert a new tempo event for all this pieces - but this is, obviously, a lot of work and can take a huge amount of time. Another idea might be to record another track where one taps the tempo with some event trigger (e.g. midi keyboard or drum pad) and let ardour use this tapping as a time reference - I do not know, if Ardour can do that and how to do it, but then again maybe this will result in even more work, as the “tapping track” itself might not be very good synchronized with the reference.

Well. I have a quite powerful computer in front of me - I believe there must be some clever algorithm that can help with this problem? I remember that some DJ software have an “auto sync” feature, also I have seen that for video editing software there exists pluraleyes, however I am not sure how these tools work and if they really could help, because I do not want to sync multiple audio tracks with constant time, I would like to generate a time reference out of an audio track with lots of time changes and these tools do not seem to be prepared for such a situation. Some beat extractor software comes to mind too, but will it work with 45 Minutes audio tracks?

What do the Ardour experts say?

Thanks for your attention!
Have a nice day,
Karma

Another aproach can be extract a tempo map using MIR (Music Information Retrival) with something like Echo Nest ( http://echonest.github.io/remix/python.html ) or Essentia ( https://github.com/MTG/essentia ) and edit the project file .ardour manually (or if you can write a script) inserting your values inside the tag.