[AC Question]

I was recording a video with my Galaxy S5 but then my battery was empty. After starting my phone again the video didn't appear in the galery. Where can I find the video that I was recording?

[Rukbat]

If you were recording to an external SD card, try PhotoRec (instructions at PhotoRec Step By Step). If you were recording to internal storage, the file probably isn't linked yet, so you'd have to use an app that lets you look through storage, block by block, and figure out where the video is - about what PhotoRec does on a computer when you plug the SD card into it (except that PhotoRec only takes hours, doing it manually, assuming you can red raw storage data, could take years).

Short answer - if you stored it internally, you probably have nothing to find.