It sounds as if it was saved on the SD card. If it was, put the card in a card reader and plug it into a computer. Download
PhotoRec, burn it to a disk and boot the computer with the disk. PhotoRec will find anything that looks like a movie (and a lot of other stuff) on the card and save it to the hard drive - but only the first 4GB probably, because hat will be all that was saved. (The FAT32 file system has an inherent limit of 4GB per file due to the math of the file system.)
If it was saved in internal storage, consider it gone.
@Nikola:
If the file is actually corrupted, it can't be recovered because the data you want to recover just isn't there. It's like finishing reading a newspaper article when someone burned the page it's continued on. PhotoRec might recover the beginning of the file - up to the point where the corruption starts, which might be almost all of it or almost none of it.