OneTaskBy Tim King · Updated
Video Duration Sum
Total Running Time of Many Video Files
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How the Video Duration Sum works
This video duration sum adds up the running time of as many clips as you drop in. It lists each file with its length, resolution and start time on a combined timeline, and shows the total with or without gaps between clips. Export the list as CSV. Only the file headers are read, in your browser.
Totting up clip lengths by hand is slow and easy to get wrong, especially with frames and hours mixed in. Editors need it for rough cuts and deliverables, teachers for course modules, and anyone filling a time slot for a screening, a broadcast break or a social upload with a length limit.
How the video duration sum works
For each file the browser opens just enough of the file to read its header, which holds the duration and picture size. It does not decode the whole video, so even large files are read in a moment. Clips are listed in the order you drop them, and each one's start time on a combined timeline is shown, adding any gap you set between clips.
| Field | What it does |
|---|---|
| Gap between clips | Seconds of black or a title card between each clip, added n − 1 times |
| Target length | A limit in minutes; the stats show how far over or under you are |
Common target lengths
| Destination | Limit |
|---|---|
| Instagram Reels | 3 minutes |
| TikTok upload | 10 minutes |
| X (Twitter) standard account | 2 minutes 20 seconds |
| YouTube unverified account | 15 minutes |
| Half-hour TV slot with adverts | about 22 minutes of programme |
Platform limits change; check the current figure before relying on one.
Tips and pitfalls
Unreadable files. If a clip uses a codec your browser cannot open, it is listed as unreadable and left out of the total. Its size still counts toward the total size.
Durations are container values. The header length can differ by a frame or two from the length an editor shows, because editors round to whole frames.
Add files in batches. Each new drop is appended to the list, so you can collect clips from several folders. Reset clears the list.
How to read the result
The total duration is the sum of all readable clips. The line with gaps adds your gap between each pair. The target line says how much time is spare or how much needs cutting.
FAQ
How do I find the total length of several videos?
Select all the files at once, or drop them in batches. Each file's duration is read from its header and added up. The total appears straight away, with a list of every clip and a CSV export.
Does it work with MOV and MKV files?
It reads any file your browser can open. Chrome and Edge read most MP4, MOV, WebM and many MKV files. Files with codecs the browser cannot open are listed as unreadable and left out of the total.
Are the videos uploaded?
No. The browser reads each file's header from your own disk to get the duration and size. Nothing is sent anywhere, and because only the header is read, large files are counted almost instantly.
Can I add a gap between clips?
Yes. Enter the gap in seconds, for example for a title card or a moment of black between clips. It is added once between each pair of clips, so ten clips with a two-second gap add eighteen seconds.
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