Issue 1678 in lilypond: Midi gives false warnings

[lilypond]

Status: Accepted
Owner: ----
Labels: Type-Defect Priority-High Regression

New issue 1678 by address@hidden: Midi gives false warnings
http://code.google.com/p/lilypond/issues/detail?id=1678

From Keith:

In a situation where you typeset several files in one run with
   lilypond *.ly
such as four movements of a piece, the internal MIDI-channel counter might
exceed 16 and give a "warning: MIDI channel wrapped around".

If each file uses 16-channels or fewer, then each MIDI file will play
just fine.

% Instead of putting many input files on the command line,
%  we can just request several MIDI files in a short test file
\score {<<
  \new Staff c
  \new Staff c
  \new Staff c
  \new Staff c >>
\midi {}  \midi {} \midi {} \midi {}
}

The simple input above demonstrates the false warning when
midiChannelMapping=#'staff, the default since version 2.13.63.

When midiChannelMapping=#'instrument, the problem does not appear until
the total number of unique instruments in all the files exceeds 16  
(counting all drumstaffs together as one).

It seems that Staff_performer::static_channel_map_ and channel_count_  
should be reset between MIDI output files.  Formerly, the channel counter  
was reset in the hconstructor for "Performance".