iPhone ran out of storage during a video
Resurecting this thread, as I want to share my experience.
https://discussions.apple.com/thread/5906520
The OP of that thread asked if there was any way to recover the video that he was shooting when the phone ran out of storage. He was effectively told to plan his life better, which I didn't feel would help him retrospectively.
The same situation happened to me today. The video appeared "gone". However, on digging into this further, I discovered about 25GB of "Other" storage used on the iPhone. I guessed that this may include the 45-minute video I'd been shooting.
I freed up a bit of space on the phone (some good tips for that are here -> https://www.macworld.com/article/232651/iphone-other-storage-what-is-it-and-how-do-you-delete-it.html) and restarted the phone. The "lost" video then appeared in the photos app.
YMMV, but I hope this hleps someone.