D&Dtools1

When you cast this spell, you immediately prepare one spell of 4th level or lower in this spell's slot.
The spell must be a spell you could normally prepare in that slot (for example, you could not prepare a wizard spell or a domain spell).
The spell works like any spell prepared in the normal manner, including requiring the normal components.
Like a bard spell, casting spellsong always requires a verbal component, and you cannot use Silent Spell or similar effects to cast the spell without a verbal component.