Recorded video with iPhone and it only shows black but theres audio

My son recently played a soccer game and i was recording most of it. He scored and I got it on video (Or so i thought). When i go to tr to watch the video it only shows black but audio is still there. When i try to edit it says" Video failed to download." It kept happening and i turned my phone off and the videos were working again but the videos that did not work before still don't. Is there any way to recover the actual "video" part? I'm quite desperate.