URL filters

Here is a plain URL for loading a J.S. Bach chorale:

http://verovio.humdrum.org/?file=chorales/chor025.krn

Single filter

Filters can be included in URLs by adding a parameter called filter followed by the filter command or a pipeline of filter commands. Here is an example of adding the string &filter= at the end of the URL, and then a filter, such as myank to extract a range of measures from the full score:

http://verovio.humdrum.org/?file=chorales/chor025.krn&filter=myank%20-m3-5

This will result in measures 3-5 of the choral being extracted from the full score and displayed in graphical notation:

The corresponding Humdrum-data embedded filter would be:

!!!filter: myank -m3-5

Percent encoding

The space character must be converted into %20 in URLs, since a space is not allowed directly in a URL. Some other characters not allowed in URLs, and their percent encoding, are:

Filter pipeline

More than one filter can be applied from the URL by separating the filters by a pipe character, |. Note that the pipe character is not allowed directly in a URL, so it must be escaped as %7c. Here is a filter pipe line that first extracts measures 3 to 5 of the score, and then changes the layout to grand-staff:

!!!filter: myank -m 3-5 | satb2gs

Some of the spaces are optional, so they are best removed when using as a URL filter to avoid unnecessary %20 encodings of space characters:

!!!filter: myank -m3-5|satb2gs

Converting this into a URL filter:

http://verovio.humdrum.org/?file=chorales/chor025.krn&filter=myank%20-m3-5%7csatb2gs

Repertory filtering

When navigating to other works/movements in the same repertory, the URL filter will be applied to the entire repertory. In addition, the filter can be added to the URL for the repertory index. Here is an example of viewing all of the Mozart piano sonatas transposed to a tonic on C (preserving the original mode):

http://verovio.humdrum.org/?file=mozart/sonatas&filter=transpose%20-kc

The filtering will not be immediately apparent, since the repertory index is displayed:

But selecting movement 1 of the Dünitz sonata will display the music in C major rather than D major:

Compiling URL filters

The results of filtering, both in the URL or embedded directly in the data, are visible in the graphical notation editor but not in the data in the text editor. To generate the notation, filters in the data or URL are applied before converting to MEI and rendered into SVG images. If you want to see resulting data from the filtering, type alt-c to compile the filter. Below is the view of the above sonata example, where the Humdrum data has now been transposed to C major as well as in the graphic notation:

With URL interface commands

Not exactly filters, but useful in combination with filter parameters are interface commands. Many interface commands (which are key combinations starting with alt) can be added to the URL. To add one or more interface commands, include the parameter &k= followed by the list of the interface command characters, excluding the alt- prefix. For example alt-y becomes &k=y. Multiple commands can be placed in the k parameter string, with no spaces needed between characters. The following URL:

http://verovio.humdrum.org/?file=mozart/sonatas/sonata06-1.krn&filter=transpose%20-kc&k=by

will hide the text editor (equivalent to typing alt-y in VHV), and will also hide the VHV logo (equivalent to typing alt-b in VHV). Here is the resulting display for the above URL: