Add `.krn`

[MarkGotham]

Dear @gregchapman-dev you absolute hero,

This is an awesome extension of music21, and a successful navigation of how to handle things since the drawbridge went up. Thanks!

Small point: any reason not to accept krn as the output type? Currently:

• the output type has to humdrum
• ... but the written extension has to be krn.

There may be some "strictly speaking" reason for this, but equally it seems worth a dash of flexibility there?

[gregchapman-dev]

Interesting. I just followed the example of other writers in music21. I see no reason not to allow this (and maybe 'kern' as well?)

[MarkGotham]

Great!

IMO any of those you can think of – anything plausible is good to include. It’s hard to imagine any being a security risk, and in the worst case, the conversion fails.

[MarkGotham]

And also .mxl. You accept compressed musicXML so it's well worth including that in the list.

[gregchapman-dev]

Well I can't do mxl, since converter21 doesn't provide a musicxml importer/exporter (just krn and mei). You'll have to write an issue against music21 for that.

[craigsapp]

mxl is a plain zip file, plus an xml header file. Rename it to *.zip and double click to see the zip contents.

Index file is /META-INF/container.xml and MusicXml file is usually score.xml, depending on where it is listed in the index file (META-INF/container.xml) in container/rootfiles/rootfile/@full-path example contents:

<?xml version="1.0" encoding="UTF-8"?>
<container>
  <rootfiles>
    <rootfile full-path="score.xml">
      </rootfile>
    </rootfiles>
  </container>

So Unzip META-INF/container.xml, read the rootfile (may conain other resouce files) to extract.

For example, VHV allows loading from compressed/uncompressed file regardless (save only to uncompresssed).

(and maybe 'kern' as well?

.krn three-letter is more common. a more generalized ending is .hmd ("HuMDrum). .krn meain that the main focus of the dta is in the **kern (as opposed to figure bass, for example).

[MarkGotham]

My experience is that converter21 not only can, but already does support .mxl.

[MarkGotham]

The .krn files in this Goudimel corpus were converted from the .mxl files there (which in turn cam from tiny notation in json but that's another story) using the script I just proposed for your README.

Hope that saves you a job!

[gregchapman-dev]

So, converter21 is two things. Mostly it is an extension for music21, containing two converters, Humdrum and MEI. It is also a simple script that uses music21 (and converter21's converters) to convert music files from one format to another. The musicxml converter that the simple script uses is in music21.

[MarkGotham]

Indeed. So including mxl as one of the approved formats for the CLI is fine right? Again, I've verified that saying musicxml but actually passing an mxl file works fine as in:

#!/bin/bash
for f in <directory_name>/*.mxl; do
  echo "Converting $f → ${f%.mxl}.krn"
  python3 -m converter21 -f musicxml -t humdrum "$f" "${f%.mxl}.krn"
done

Up to you. Seems a shame that -f mxl raises an error when the functionality is there, but maybe you prefer to keep it that way.

[gregchapman-dev]

I guess I could put a format code translation layer in the command line code. I'll put it on the to do list.