Instagram Reels autoplay silently in the feed. The majority of Reels views happen without the viewer ever tapping to unmute — particularly when someone is scrolling in public, at work, or in bed. A Reel without captions communicates nothing to these viewers. Burned-in captions — permanently embedded into the video frames — are the only reliable way to ensure every viewer can follow your content regardless of sound. This guide covers the complete free workflow for adding captions to any Reel before upload.
Why Burned-In Captions, Not Uploaded SRT
Instagram does allow caption uploads via the accessibility settings when posting a Reel, but this approach has significant limitations: the caption display depends on the viewer’s Instagram settings, the rendering quality is inconsistent across devices, and the caption file can fail to sync on some versions of the app. Burned-in (open) captions are always visible to every viewer, on every device, without any viewer action required. For a full explanation of the difference, see the guide on closed captions vs. open captions.
Instagram Reels Specs (Caption-Ready Format)
| Spec | Requirement |
|---|---|
| Aspect ratio | 9:16 vertical (1080×1920) |
| Format | MP4 (H.264) |
| Duration | Up to 90 seconds |
| File size | Under 4 GB (typically well under 500 MB for <90 sec) |
| Caption safe zone | Keep captions in the centre 80% of the frame — avoid the very top and bottom 10% where Instagram’s UI overlays appear |
Step-by-Step: Adding Burned-In Captions to a Reel
Your Reel should already be in 9:16 vertical format (1080×1920) and trimmed to the correct length. If it’s currently landscape or square, convert it using the Format Converter. If it needs trimming, use the Video Trimmer first. Always add captions last, after all cropping and trimming is complete — if you crop after captioning, the caption positions will be wrong.
Transcribe your audio and create a timed SRT file using the free Text to SRT tool. Paste your transcript, set approximate timing for each line, and download the .srt file. For tips on SRT format and timecoding, see the SRT file format guide. Keep each line short — 4–6 words maximum works best for Reels at mobile viewing size.
Open the free Add Subtitles tool. Load your vertical video and upload the SRT file. Set caption position to lower-centre — not at the very bottom edge. Choose a large font size (the video is viewed on a small phone screen), white text with a dark outline or background for readability on any footage. Apply and download.
Reels under 90 seconds are typically well under Instagram’s size limit. If your file is unusually large, run it through the Video Compressor before uploading.
Post the finished .mp4 file as a Reel. The captions are burned into the video and will appear for every viewer automatically, with no extra steps required on their end. You can still add Instagram’s native auto-captions as a redundancy layer if desired — they won’t conflict with the burned-in captions.
Caption Style Tips for Reels
- Font size: larger than you think you need — Reels are watched on phone screens at arm’s length, often in bright light
- Contrast: white text on a dark semi-transparent background band reads on any footage colour; white text with dark stroke is an alternative for a cleaner look
- Lines per entry: 1–2 lines maximum; 4–6 words per line for comfortable reading pace
- Timing: captions should display for long enough to be read at a comfortable pace — minimum 1.5 seconds per line, ideally 2–3 seconds
- Position: lower-centre, clear of the Instagram UI overlay zone at the very bottom
- Format: 9:16 vertical, 1080×1920, MP4 H.264
- Trim and crop BEFORE captioning — always caption last
- Create SRT with Text to SRT — 4–6 words per line
- Burn captions with Add Subtitles — lower-centre, large font, high contrast
- Avoid bottom 15% of frame — Instagram UI overlaps there
- Same captioned file works for TikTok and YouTube Shorts