mkvideo, sync to recorded audio

[Christian Alpen]

Hi,

once again I have a question concerning generating video with 
mkvideo-lily-diff:

I want to synchronize the video to a manually recorded audio track with 
rubato and tempo variations.
Somewhere I read about how to generate an extra file containing these 
tempo informations (using extra software
to create scores from contemporary and not yet notated music) and how to 
use it to extract these information for
mkvideo generating the video.

The problem is: After googling a lot around I cannot find this guide again.
So I'm looking for help on how this is done or, if anyone knows or 
remembers, a link to this guide.

Can anyone help me with this?

Thanks a lot,

Christian