How to add subtitles to a long video

Two jobs hiding behind one search

People who search for a subtitle generator for a long video usually want one of two things, and the right tool is different for each.

• One captioned file of the whole recording, for people who watch it start to finish or who need captions for access.
• Short captioned moments pulled out of the recording, to post on Shorts, Reels or TikTok.

The first job is about completeness. Every sentence has to be in the captions. The second job is about selection: out of two hours, which ninety seconds deserve to be seen, and do they have captions people can read on a phone with the sound off? KeyMo does the second job. It does not hand back your two-hour video with subtitles on it.

Why an hour of speech is harder to caption than it looks

Automatic captions are a starting point, not a finished product. YouTube says its automatic captions come from machine learning, that quality varies, and that they should always be reviewed and edited. The W3C accessibility pages go further: automatically generated captions do not meet user needs unless they are confirmed to be fully accurate, and usually need significant editing. Their example is a single missing word such as "not", which can make a caption say the opposite of what was said.

Now multiply that by length. YouTube's own help page says its Auto-sync tool, which times a transcript you supply, is not recommended for videos over an hour or with poor audio. A two-hour interview with two guests, crosstalk and a bad phone line in the middle is exactly that case. The W3C notes that even correcting an automatic caption file takes quite a bit of time for people who do not do it regularly.

Clips change the arithmetic. If you only publish the best fifteen moments, you only have to read the captions on those fifteen.

Worked example: a 2-hour interview in, captioned clips out

Take a recorded interview that runs 2 hours, which is 120 minutes. It sits inside KeyMo's 5 minute to 3 hour range, so it can be uploaded as MP4 or MOV (up to 10 GB) or pasted as a YouTube link on a paid plan.

For a source longer than 60 minutes, KeyMo's built-in target is up to 15 clips. That is a target, not a promise. Each clip gets a score out of 10 with a one-line reason, and only clips scoring 7 or higher are kept, so a flat conversation can return fewer.

So the two hours become, at most, about 22 minutes of vertical video, 1080x1920 at 30 fps, with the captions already drawn in. Each clip uses one of 12 caption styles with word-by-word timing, and you can switch a style in the editor if the default does not suit the speaker.

Limits to check before you upload

• Length: 5 minutes to 3 hours per source video. A 4-hour recording has to be split before it goes in.
• File: MP4 or MOV, up to 10 GB.
• Link import: paid plans only, fetches up to 1080p, and you confirm that you own the video or have permission to use it.
• Output: vertical 9:16 only. There is no 16:9 export and no watermark on any plan.
• Storage: source files are kept for 7 days and finished clips for 30 days, so download what you want to keep.
• No free plan and no trial. The cheapest plan is Starter at $12 a month.

When this is the wrong tool

Use a different route if a viewer needs the full recording captioned, for example a lecture, a training video or anything that must be accessible start to finish. For that, upload a caption file or edit captions in a tool made for whole-video subtitles. YouTube lists the file types it accepts, and the plain SRT and SBV types are the ones it suggests for beginners. Our guide to SRT versus VTT covers the formats.

Use KeyMo when the goal is reach: you have a long podcast or interview and want the strongest moments as captioned vertical clips. If that is you, the steps are short.

1. Upload the file, or paste the YouTube link if you are on a paid plan.
2. Pick a clip length (Auto, Short, Medium or Long) and a caption style.
3. Read the score and one-line reason on each clip and keep the ones you would post.
4. Open any clip to change what you do not like, then export, or download all clips as one ZIP.

More detail on the clipping side is in how to clip a podcast, and long video to Shorts covers the same flow for non-podcast footage. Plans are on the pricing page.