少し脱線。
こういうスコアをエクスポートした場合、以下のような.musicxmlが出力される。
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE score-partwise PUBLIC "-//Recordare//DTD MusicXML 3.1 Partwise//EN" "http://www.musicxml.org/dtds/partwise.dtd">
<score-partwise version="3.1">
<work>
<work-title>Title</work-title>
</work>
<identification>
<creator type="composer">Composer</creator>
<encoding>
<software>MuseScore 3.4.2</software>
<encoding-date>2020-03-05</encoding-date>
<supports element="accidental" type="yes"/>
<supports element="beam" type="yes"/>
<supports element="print" attribute="new-page" type="yes" value="yes"/>
<supports element="print" attribute="new-system" type="yes" value="yes"/>
<supports element="stem" type="yes"/>
</encoding>
</identification>
<defaults>
<scaling>
<millimeters>7.05556</millimeters>
<tenths>40</tenths>
</scaling>
<page-layout>
<page-height>1683.36</page-height>
<page-width>1190.88</page-width>
<page-margins type="even">
<left-margin>56.6929</left-margin>
<right-margin>56.6929</right-margin>
<top-margin>56.6929</top-margin>
<bottom-margin>113.386</bottom-margin>
</page-margins>
<page-margins type="odd">
<left-margin>56.6929</left-margin>
<right-margin>56.6929</right-margin>
<top-margin>56.6929</top-margin>
<bottom-margin>113.386</bottom-margin>
</page-margins>
</page-layout>
<word-font font-family="FreeSerif" font-size="10"/>
<lyric-font font-family="FreeSerif" font-size="11"/>
</defaults>
<credit page="1">
<credit-words default-x="595.44" default-y="1626.67" justify="center" valign="top" font-size="24">Title</credit-words>
</credit>
<credit page="1">
<credit-words default-x="1134.19" default-y="1526.67" justify="right" valign="bottom" font-size="12">Composer</credit-words>
</credit>
<part-list>
<score-part id="P1">
<part-name>Piano</part-name>
<part-abbreviation>Pno.</part-abbreviation>
<score-instrument id="P1-I1">
<instrument-name>Piano</instrument-name>
</score-instrument>
<midi-device id="P1-I1" port="1"></midi-device>
<midi-instrument id="P1-I1">
<midi-channel>1</midi-channel>
<midi-program>1</midi-program>
<volume>78.7402</volume>
<pan>0</pan>
</midi-instrument>
</score-part>
</part-list>
<part id="P1">
<measure number="1" width="372.34">
<print>
<system-layout>
<system-margins>
<left-margin>0.00</left-margin>
<right-margin>0.00</right-margin>
</system-margins>
<top-system-distance>170.00</top-system-distance>
</system-layout>
</print>
<attributes>
<divisions>4</divisions>
<key>
<fifths>0</fifths>
</key>
<time>
<beats>4</beats>
<beat-type>4</beat-type>
</time>
</attributes>
<note default-x="83.07" default-y="-50.00">
<pitch>
<step>C</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<voice>1</voice>
<type>quarter</type>
<stem>up</stem>
<lyric number="1" default-x="6.58" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>ど</text>
</lyric>
</note>
<note default-x="154.99" default-y="-45.00">
<pitch>
<step>D</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<voice>1</voice>
<type>quarter</type>
<stem>up</stem>
<lyric number="1" default-x="6.58" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>れ</text>
</lyric>
</note>
<note default-x="226.90" default-y="-40.00">
<pitch>
<step>E</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<voice>1</voice>
<type>quarter</type>
<stem>up</stem>
<lyric number="1" default-x="6.58" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>み</text>
</lyric>
</note>
<note default-x="298.82" default-y="-35.00">
<pitch>
<step>F</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<voice>1</voice>
<type>quarter</type>
<stem>up</stem>
<lyric number="1" default-x="6.58" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>ふぁ</text>
</lyric>
</note>
</measure>
<measure number="2" width="278.59">
<note default-x="10.54" default-y="-30.00">
<pitch>
<step>G</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<voice>1</voice>
<type>quarter</type>
<stem>up</stem>
<lyric number="1" default-x="6.58" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>ソ</text>
</lyric>
</note>
<note default-x="78.70" default-y="-25.00">
<pitch>
<step>A</step>
<octave>4</octave>
</pitch>
<duration>2</duration>
<voice>1</voice>
<type>eighth</type>
<stem>up</stem>
<beam number="1">begin</beam>
<lyric number="1" default-x="6.58" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>ラ</text>
</lyric>
</note>
<note default-x="128.28" default-y="-20.00">
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>1</duration>
<voice>1</voice>
<type>16th</type>
<stem>up</stem>
<beam number="1">end</beam>
<beam number="2">backward hook</beam>
<lyric number="1" default-x="6.58" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>シ</text>
</lyric>
</note>
<note>
<rest/>
<duration>1</duration>
<voice>1</voice>
<type>16th</type>
</note>
<note default-x="189.88" default-y="-20.00">
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>8</duration>
<voice>1</voice>
<type>half</type>
<stem>down</stem>
<lyric number="1" default-x="6.94" default-y="-53.02" relative-y="-30.00">
<syllabic>single</syllabic>
<text>ド</text>
</lyric>
</note>
</measure>
<measure number="3" width="213.28">
<note>
<rest/>
<duration>16</duration>
<voice>1</voice>
</note>
</measure>
<measure number="4" width="213.28">
<note>
<rest/>
<duration>16</duration>
<voice>1</voice>
</note>
<barline location="right">
<bar-style>light-heavy</bar-style>
</barline>
</measure>
</part>
</score-partwise>
長い…。自分で書くのはとても無理。
ただ、かなりの情報がMuseScoreの編集のためにあるもののはずで、NEUTRINOに渡すものはもっとシンプルでいいはず。
ということで色々削ってみた結果、以下のXMLでも行けた。 （仕様上必須のとかも削っちゃってるかもしれないけど、実験なのでよしとする）
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE score-partwise PUBLIC "-//Recordare//DTD MusicXML 3.1 Partwise//EN" "http://www.musicxml.org/dtds/partwise.dtd">
<score-partwise version="3.1">
<part>
<measure>
<attributes>
<divisions>4</divisions>
<key>
<fifths>0</fifths>
</key>
<time>
<beats>4</beats>
<beat-type>4</beat-type>
</time>
<clef>
<sign>G</sign>
<line>2</line>
</clef>
</attributes>
<note>
<pitch>
<step>C</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<lyric>
<text>ど</text>
</lyric>
</note>
<note>
<pitch>
<step>D</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<lyric>
<text>れ</text>
</lyric>
</note>
<note>
<pitch>
<step>E</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<lyric>
<text>み</text>
</lyric>
</note>
<note>
<pitch>
<step>F</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<lyric>
<text>ふぁ</text>
</lyric>
</note>
</measure>
<measure>
<note>
<pitch>
<step>G</step>
<octave>4</octave>
</pitch>
<duration>4</duration>
<lyric>
<text>ソ</text>
</lyric>
</note>
<note>
<pitch>
<step>A</step>
<octave>4</octave>
</pitch>
<duration>2</duration>
<lyric>
<text>ラ</text>
</lyric>
</note>
<note>
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>1</duration>
<lyric>
<text>シ</text>
</lyric>
</note>
<note>
<rest/>
<duration>1</duration>
</note>
<note>
<pitch>
<step>B</step>
<octave>4</octave>
</pitch>
<duration>8</duration>
<lyric>
<text>ド</text>
</lyric>
</note>
</measure>
<measure>
<note>
<rest/>
<duration>16</duration>
</note>
</measure>
<measure>
<note>
<rest/>
<duration>16</duration>
</note>
</measure>
</part>
</score-partwise>
これなら自分でXMLを生成するのも無理ではないか？と思える長さにはなった。