Search by everything else the file still carries. A video file keeps a date, a length, a size and a folder. Phone and camera footage usually also stores the capture date and the device inside the file. Your operating system can filter on most of that. If filtering doesn't narrow it down, look at where the video was used, because an editing project, a sent message or an upload page points straight back to the file. If all you remember is what happens in the video, you need search that reads the content. That can be a transcript you make yourself, your phone's photo app, or a tool that indexes footage.
Start with what the file still knows
Limit the search to video files and sort by date. Windows File Explorer and macOS Finder both let you narrow by file type and date range, and that alone often shrinks a whole drive down to one screen of candidates.
Don't trust dates too far. Copying a file to a new drive can reset its created date to the day of the copy, so a clip shot two summers ago can show up as last month. The modified date often survives the copy, and the capture date stored inside phone and camera files survives better still. On a Mac, Get Info shows a video's duration. In Windows Explorer you can add a Length column. If you remember it was a long interview and not a quick clip, sorting by length or size cuts the list fast.
Phone footage is easier. Phone photo apps group videos by capture date and often by location, and most of them can search for things that appear in the picture, such as a dog or a beach. If the video was shot on a phone, look there before you touch the computer.
Look where the video was used
Files rarely vanish on their own. Usually they got used somewhere. If the video went into an edit, the editing project still stores the path to every clip in it, and most editors can show a clip's file location from the timeline. If you sent it to someone, the message or email has it attached, with a date. If you uploaded it anywhere, the upload has a title and a date that tell you roughly when the file was made, which takes you back to the date filter above.
When all you remember is what happens in it
This is the hard case, and there are three ways to handle it.
The first is scrubbing by eye. Switch the folder to large thumbnails and preview files one at a time. It's free and fine for a small folder. It gets slow once the files are long recordings, because a thumbnail shows one frame of an hour.
The second is making a transcript. Run speech-to-text over the folder and search the text. If you remember a phrase, this works well, and it's cheap or free if you run it yourself. It misses everything nobody says out loud: a whiteboard, a product on a table, the moment someone laughs.
The third is indexing the content. A search layer takes footage you upload, indexes it once, and then answers plain-language descriptions of what was said or shown. The cost is the upload itself, plus paying for usage past whatever free tier the tool has. You still have to check what comes back. Some tools return whole files and others return time ranges inside them, and if the question is "which file was it," a list of whole files that might match already answers it. In Vivu, for example, once the recordings are uploaded to a project, a description like "someone admits they get nervous before going on stage" can come back with time ranges from several different recordings, each with a short reason. Some results will be only loosely related, and deciding which ones count is still up to you.
If what you have is one remembered scene, working from a remembered scene goes into that case in more detail.
If it was someone else's video you saw online
If you don't know what it was called because it wasn't yours, start with your watch history on the platform where you saw it, then your browser history around the day you remember watching it. Searching for a description of the content plus the platform's name gets you surprisingly far. If you have a screenshot or can grab a frame, a reverse image search on a frame is often quicker than describing it.
When you don't need a search tool at all
If you lose a file once a year and your footage lives in one folder, dates and thumbnails will find it. Content search pays off when the same kind of question keeps coming back across a big pile of long recordings, where scrubbing through each one is the real cost. For most people the cheaper long-term fix is naming files at import with a date and a subject, or letting software handle some of that with automatic tagging.
Which kind of lost is yours
If you remember roughly when, the file's dates will get you there. If you remember where it went, the project or the message will. Search over the content is only worth setting up when all you remember is what happens on screen, and even then it's worth asking how often you'll need to ask that kind of question again.
FAQ
Can Windows or Mac search find a video by what's in it?
No. File search on both systems works from filenames and metadata such as type, date and size. It won't find a video by what's said or shown in it.
Phone photo apps are the exception most people already have, since many of them can search videos for things that appear in the picture.
Why does my video show the wrong date?
Copying or downloading a file often sets its created date to the day of the copy. The modified date usually survives. Phone and camera footage also stores a capture date inside the file, and photo apps and media players read that even when the file system date is wrong.
Sort by modified date or check the file's detailed properties before you give up on a date range.
Can I search a folder of videos for something someone said?
Yes, if you turn the audio into text first. Speech-to-text tools, including free ones you can run on your own computer, produce a transcript for each file, and any text search will then find the phrase and the file it came from.
Accuracy drops with background music, people talking over each other and heavy accents, so search for a distinctive word instead of a full sentence.