Caption Checker
Drop in an SRT or VTT file, or paste a link to one. Choose where the video will play and see every caption that is too long, too fast, too brief or overlapping, then download a fixed copy as SRT or VTT.
Where will these captions play?
42 characters a line, 2 lines, up to 20 characters a second; at least 1 s on screen.
- Fit. Characters per line and lines per caption, for landscape video or vertical shorts.
- Speed. Characters a second, so nobody is still reading when the caption changes.
- Timing. Captions that flash by, stay too long, overlap or leave a flicker gap.
- Readability. Lines that break mid-phrase, filler words, all capitals and repeated captions.
How many characters should a caption line have?
About 42 characters a line and no more than two lines is the common limit for landscape video on websites, YouTube and streaming. Burned-in captions on vertical shorts need shorter lines, around 32 characters, so they fit a phone screen without covering the speaker. The checker uses those limits for each setting.
What reading speed should captions have?
Up to about 20 characters a second works for most web and social video. Streaming and broadcast guidelines for adult viewers often use 17. Above that, viewers cannot finish reading before the caption changes. The fix is a shorter wording or more time on screen, which the checker shows caption by caption.
What does the fixed copy change?
Only what can be changed safely without a person: long lines are re-broken into balanced lines at a natural phrase break, overlapping captions are trimmed so only one shows at a time, very short captions are held longer where there is a gap, flicker gaps are closed, empty captions are removed and, if you tick it, um and uh are dropped. It never rewrites wording or moves a caption across speech.
Can it read captions from YouTube or my video platform?
Paste a direct link to an .srt or .vtt file, a page whose video has a caption track, or your podcast's RSS feed or Apple Podcasts link if your host publishes SRT or VTT transcripts. YouTube and most video platforms keep captions inside the player, so download the file from YouTube Studio or your platform and drop it in.
Does it convert SRT to VTT?
Yes. Whatever you load, you can download the fixed copy as SRT or as WebVTT, the format browsers use for video on a web page.
Is my caption file uploaded?
No. Files you drop in or paste are checked in your browser. When you paste a link, FDM's server reads that public file once and sends it back to your browser; it is not stored.
Can FDM caption our videos?
Yes. FDM's podcast and short-form edits include readable captions, for the full episode and for the vertical cutdowns made from it.