What it means
ば〇〇のに expresses regret about an unreal condition and an unrealized or undesirable result. It means “If only...” or “If ..., it would have ...,” with the result often understood rather than stated. The condition usually describes something that did not happen or is not true, while the final のに adds a feeling of disappointment, frustration, or longing.
Usage note
At the end of a sentence, のに here expresses regret and should not be confused with the conjunction のに meaning “although” or “despite.” For nouns and na-adjectives, なら is used instead of a form ending in ば.
Example sentences
もう少し早く出発すれば、最終バスに間に合ったのに。
If only I had left a little earlier, I would have caught the last bus.
地図があれば、道に迷わなかったのに。
If only I had had a map, I would not have gotten lost.
もう少し静かなら、赤ちゃんはすぐ眠れたのに。
If it had been a little quieter, the baby would have fallen asleep right away.