As an engraver AND an independent publisher (both of printed, and soon digital interactive sheet music) it has been imperitive for my to find ways of efficiently separting the content from the actual publishing layout, so that changes to format and/or content can be easily managed without one being entirely dependent on the other.
As a printing method, all my sheet music content is imported as linked graphics into my desktop publishing software so that as soon as a change is made and the relevant piece of music is recompiled, my layout document automatically is updated with the new graphic content. I don't know how a larger publisher would work, but I would imagine they would follow some similar principle so that tweaks could easily be made without having to modify the layout.
I've been following the MusicXML export discussion closely, because I have also been looking at converting some sheet music content into MusicXML so it can be delivered by the Legato Music interactive sheet music viewer. As I delve deeper into the process, I don't see how I can avoid having to make formatting/layout changes to the version that is delivered as interactive sheet music. So that even if there were a smooth export process from Lilypond to MusicXML, I would still need to tweak the formatting and layout, perhaps significantly. It would almost make my life easier just to have a fast, precise way to deliver the content rather than a way of trying to retain the precise format. I wind up doing my formatting in Finale, since the Legato support folks recommend the MusicXML export from Finale (using Recordare's export plugins) as the cleanest output for the Legato music player.
By the way, I'll contribute $75 US to the MusicXML exporter project(s).
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Jack Cooper, BerLen Music
www.berlenmusic.com
www.jack-cooper.com