1. In the other app, export or share your work as audio (WAV, M4A, AIFF or MP3): the whole beat, each part on its own (often called stems), or single sounds.
  2. Tap Share there and choose Blackcap — or here, More → Bring In From Another App… → Choose Files… (pick several at once).
  3. Blackcap shows where each goes: longer files become your own tracks, lined up from bar 1; short sounds go on the Sampler's empty pads.
  4. It listens to the parts together for the tempo, key and chords. Set the tempo to match (so the bars line up), and build the Chart from the chords if you like.
  5. Bring It In. One Undo takes it all out again. Then add a verse, a chorus, vocals — the rest of the song.

MIDI files come in too (from NanoStudio, a desktop music app, or a website): choose a .mid file the same way. The drums go on the beat, every other part onto its own Keys layer with a sound to match, and the song takes the file's tempo. One Undo takes it back.

Another app's own project file can't be opened, only the audio or MIDI it exports. A zip of files needs opening in the Files app first.