Yes, Keira Knightley is actually singing in "Begin Again." She portrays a singer-songwriter named Gretta, and her performances in the film feature her real vocal work. Knightley trained for the role, taking vocal lessons to prepare for the music aspects of her character. The film showcases her singing several original songs, contributing to the story's emotional depth and authenticity.

"Begin Again" is generally well-received, praised for its heartfelt storytelling and strong performances, particularly by Keira Knightley and Mark Ruffalo. The film explores themes of love, loss, and artistic rebirth, set against the backdrop of New York City's music scene. Critics commend its charming direction by John Carney and the engaging soundtrack. While some viewers may find the plot predictable, many appreciate its uplifting message and emotional depth. Overall, if you enjoy music-driven dramas with a focus on personal growth, it's worth watching.

As of October 2023, "Begin Again" is not available on Netflix. However, the movie may be available on other streaming platforms or for rent/purchase through services like Amazon Prime Video, Apple iTunes, or Google Play. Availability can vary by region, so it's a good idea to check your local streaming services for the most accurate information.