For a project I am currently working on I need individual midi files of single piano notes as though the note was held for 4 seconds before release. I have found a few toy online midi keyboards that can generate the exact notes desired, but there is no output option. What software (Windows or linux) would allow me to generate a specific piano key and output that note as a file? I have played around with rosegarden and been unsuccessful, and I do not have access to a physical synthesizer or keyboard.
Rosegarden should do the job.
If you have programming skills, it is extremely easy to generate MIDI files like this with python or perl and the appropriate MIDI library.
Along similar lines, I wrote some tiny Pure Data patches for holding long, droning notes. You can get them at the Pure Data forum (you have to sign in to see the attached files).
Update - here are the Pure Data patches on github.
I thought that rosegarden could export to .midi files...
Nevertheless here you have a list
Some of them GPL.