Note that this does not work in all browsers. I couldn't get it working on Chrome on an iPhone or on Safari on a Mac, but that's no huge surprise.
Sometimes you can drag and drop a music image directly into the top image field, but this won't usually work. This is something I can't work around, as it's the source site that allows or denies this. (The problem is CORS, if you're curious)
If you can't drag and drop, you'll have to:
Some OSes will let you streamline this, such as letting you drag the image onto your desktop, and then drag that file into the image field, or copy the image and paste it into the file dialog.
Aside: If you know a way to work around it, please go to the repository and ping me in the issues. I would absolutely love to have drag-and-drop functionality.
You can make your own by getting your own image and loading it with "Load Input Image..." or dragging and dropping it over the bottom image (the same caveats apply here about cross-site drag and drop as above). You can convert musicxml music to the TOML format that imagemusic uses, but it only supports a limited format, and specifically needs partwise musicxml, not timewise. You can use musescore to generate musicxml that should work from midis. You can find midis by going to musescore, or for video game music to VGMusic. If you find a site that lets you either get musicxml or midi, you should (counter-intuitively) probably go for the midi, because it's a simpler format and musicxml is more likely to have constructs that imagemusic won't convert well, like grace notes. Also make sure to remove all percussion tracsk, as that isn't yet supported. Keeping percussion tracks in the mix will likely cause errors. To summarize:
The musicxml converter is also still pretty fresh and likely still quite buggy. If you can find a small musicxml file that produces bad behavior with the converter, you can submit it as a bug report on the issue tracker (see the bottom of this page).
When your music is converted, you can review the TOML and maybe change some instruments and stuff. The conversion is very simple and will not try to take anything like volume or instruments into account, so you may want to tweak it and try it multiple times to get the best results. If you have trouble with getting good results because one voice is too complex (like volume changes), your best bet is to use musescore or some other music editor to separate them into separate voices before importing them again.
Once you have an image in the bottom image and valid music TOML in the text box, you can "Bake Song Into Image" to get your baked image, and "Play Music Image" to test it out.
Once you have your baked music image, you can share it wherever you like, and people can use your image to hear whatever song you baked into it.
The music format is fairly self-descriptive. A song is composed of ticks_per_second and a list of voices. Each voice has a [[voice]] section, containing its volume, its instrument, its notes, and its envelope.
Volume is a number from 0 to 255 giving the volume of the voice.
Instrument is either Sawtooth, Sine, Square, or Triangle. More instruments and percussion may come in the future.
A string of notes. Each note is composed of a length (in ticks), the note name, and the octave. So a middle-C quarter note might be 2c4, if each tick is an eighth note. Rests are just a length and the letter r.
The envelope is how an individual note's volume is modulated. It is composed of points. Each point has a stop and an amplitude. The stop is in hundredths of seconds, and when positive, indicates a time length from the beginning of the note, and when negative, indicates a time length from the end of the note. Amplitude is a volume value from 0 to 255, similarly to the volume above.
When a note is being processed, the envelope is first put into terms of absolute time, and the stops are taken from left to right. Any stops before the beginning of the note, after the end of the note, or out of order are removed.
You can use the envelope to get quite complex musical effects.
Please report it! This repository has its home on GitLab, which is the preferred place to report issues, but it is cloned on GitHub and issues are being watched as well. If you can provide files to replicate it, that would greatly help. The smaller you can get these files, the better.