Burn Subtitles into Video

Burning subtitles into video — also called hardcoding, open captioning, or baking in subtitles — means rendering the subtitle text directly into the video frame so that it becomes part of the video itself. Unlike soft subtitles (SRT/VTT files), burned subtitles cannot be turned off, hidden, or removed. They are always visible on every platform and every player.

Soft captions vs burned captions — when to use each

Soft subtitles (SRT, VTT) are separate files that a player overlays on the video at playback. The viewer can toggle them on or off. They're the right choice when: you're uploading to a platform that supports caption tracks (YouTube, Vimeo, Netflix), you want viewers to be able to turn subtitles off, or you need multiple language tracks.

Burned subtitles (open captions) are permanently part of the video frame. They're the right choice when: you're posting to a platform that doesn't support caption tracks (Instagram Reels, TikTok, Twitter/X), you want captions on by default for all viewers, or you're distributing a final master file where caption files won't travel with the video.

Why burned subtitles matter for social media

Most social media video is watched without sound. Instagram, TikTok, Twitter/X, and LinkedIn all autoplay video with sound off by default. Burned subtitles ensure your message reaches viewers who are scrolling silently — which, depending on the platform, is 60–85% of your audience. Studies consistently show that captioned social media videos receive significantly more views, shares, and watch-through.

Additionally, platforms like Instagram and TikTok do not support separate caption file uploads for Reels and short-form content. Burned subtitles are the only way to ensure captions show for every viewer on these platforms.

How AudioSRT uses FFmpeg.wasm to render locally

FFmpeg is the industry-standard open-source multimedia processing library used by YouTube, Netflix, VLC, and virtually every professional video tool. AudioSRT uses FFmpeg.wasm — a WebAssembly port of FFmpeg — to run video rendering directly in your browser without any server interaction.

When you click "Export Burned MP4", AudioSRT passes your video file, subtitle track, and styling settings to FFmpeg.wasm. FFmpeg renders each video frame with the subtitle text overlaid, then re-encodes the video at the same resolution and bitrate as the original. The final MP4 is written directly to your downloads folder. No upload, no cloud rendering queue, no waiting for a server response.

Step-by-step burning workflow

1. Upload your video. Drop an MP4, MOV or WebM into AudioSRT. The video is read locally — nothing is uploaded.
2. Transcribe or import subtitles. Let Whisper AI transcribe the audio, or upload an existing SRT file to skip transcription entirely.
3. Edit subtitles. Fix any transcription errors, split long lines, and adjust timing. This is your last chance to correct subtitles before they're permanently embedded.
4. Style your subtitles. Use AudioSRT's styling panel to set font, size, color, shadow, stroke and position. The live preview shows exactly how they'll look burned into the video.
5. Export burned MP4. Click Export and select "Burned MP4". FFmpeg begins rendering. A progress bar shows rendering progress.
6. Download and verify. Once rendering is complete, the burned MP4 downloads automatically. Play it in any video player to verify subtitles appear correctly before publishing.

Typography tips for burned subtitles

Burned subtitle typography is more important than soft subtitle typography — once burned, you can't change it. Key considerations:

• High contrast. White text with a dark stroke or drop shadow reads on any background. Avoid light-colored text on light backgrounds — it becomes unreadable on certain frames.
• Generous size. For horizontal (16:9) video: 40–48px at 1080p. For vertical (9:16) video: 52–64px. Burned subtitles often look smaller than expected in the final output — go slightly larger than you think you need.
• Position carefully. For horizontal video, bottom-center is standard. For vertical video (Instagram Reels, TikToks), center-screen positioning avoids UI overlays at the top and bottom of the frame.
• Stroke vs shadow. A 2–3px stroke (outline) makes text readable on any background color. A drop shadow adds depth but can look softer. For social media, stroke tends to perform better on variable backgrounds.

Platform-specific considerations

Instagram Reels and TikTok: Use vertical (9:16) video with subtitles positioned in the center third of the frame, avoiding the top 15% (for the avatar/username UI) and bottom 20% (for the like/comment UI). Font size 54–64px at 1080×1920.

YouTube: Burned subtitles on YouTube are not recommended if you also want closed captions — you'll end up with text appearing twice. For YouTube, use soft subtitle SRT upload instead.

LinkedIn and Twitter/X: Burned subtitles work well for these platforms. Standard horizontal (16:9) format, bottom-center position, 40–48px font size at 1080p.

File size and quality after burning

Burning subtitles requires re-encoding the video, which always involves some quality trade-off compared to the source. AudioSRT uses FFmpeg's default quality settings, which preserve visual quality closely to the source for most content types. File size after burning is similar to the original — subtitle text adds minimal data compared to the video frames themselves.

If file size is a concern (for example, uploading to a platform with a size limit), AudioSRT does not currently offer custom bitrate settings for burned export. Export the burned MP4 and compress it separately with HandBrake or a similar tool if you need to reduce file size further.

Common mistakes with burned subtitles

• Not reviewing the preview before burning. Once burned, subtitles cannot be removed without re-rendering. Always check the live preview carefully before starting the render.
• Lines too long. Long subtitle lines at large font sizes may extend off the edge of the frame. Keep lines under 35 characters for burned subtitles — more conservative than soft subtitles.
• Position conflicts with UI. Platform UI overlays (play button, username, hashtags) can cover burned subtitles. Check platform-specific safe zones before finalizing position.
• Burning instead of uploading SRT to YouTube. YouTube will show burned subtitles and closed captions simultaneously if both are present. For YouTube, use soft subtitle upload instead.