Subtitle Formats Explained: SRT, VTT, ASS, and SSA Compared
Subtitles come in a dozen different formats. Each platform and media player has its own preferences and limitations. This guide helps you pick the right format and convert between them without losing styling.
SRT (SubRip Text)
SRT is the most universal subtitle format. It's a plain text file with a straightforward structure:
1
00:00:01,000 --> 00:00:04,000
Welcome to the file conversion tutorial.
2
00:00:05,500 --> 00:00:09,000
Today we'll learn about subtitle formats.
- Strengths: compatible with virtually every media player, platform, and social network (YouTube, Vimeo, Facebook)
- Limitations: only supports basic HTML formatting (
<b>,<i>,<u>,<font color>) - Best for: general distribution, YouTube, local video files
VTT (WebVTT)
VTT is the web standard defined by the W3C. Nearly identical to SRT but with a few improvements:
WEBVTT
00:00:01.000 --> 00:00:04.000
Welcome to the tutorial.
00:00:05.500 --> 00:00:09.000
<b>Bold text</b> with more styling options.
- Differs from SRT: uses a period (
.) instead of a comma for milliseconds; supports region metadata and positioning - Best for: HTML5 video with
<track>element, modern web platforms - Compatibility: Chrome, Firefox, Safari, Edge natively
ASS / SSA (Advanced SubStation Alpha)
ASS (also called SSA) is the format with the greatest typographic control. It supports:
- Custom fonts, sizes, and colors
- Precise on-screen positioning
- Karaoke animations and effects
- Multiple styles in a single file
It's the de facto standard in anime fansubs and productions with stylized subtitles.
- Strengths: maximum visual control, ideal for anime and styled content
- Limitations: only readable by VLC, MPC-HC, mpv, and some advanced players. YouTube ignores it.
- Best for: fansubs, anime, local MKV files
Format comparison table
| Format | Styling | Web | Players | Streaming |
|---|---|---|---|---|
| SRT | Basic | Yes | All | Yes |
| VTT | Medium | Native HTML5 | Modern | Yes |
| ASS/SSA | Full | No | Few | No |
| SUB (MicroDVD) | None | No | Some | No |
How to convert between subtitle formats
- Go to KaijuConverter — SRT to VTT (or whichever pair you need)
- Upload your subtitle file
- Download in the target format
Note on ASS → SRT: converting from ASS loses all advanced styles (colors, positions, animations). Text is preserved but the visual formatting becomes plain.
Adding subtitles to an MP4 file
Soft subtitles (external, not burned in)
The subtitle file travels alongside the video:
ffmpeg -i video.mp4 -i subtitles.srt -c copy -c:s mov_text video_with_subs.mp4
Hard subtitles (burned into the video)
Subtitles are permanently embedded in the picture:
ffmpeg -i video.mp4 -vf subtitles=subtitles.srt video_hardcoded.mp4
Soft subtitles are preferable because viewers can toggle them on and off. Hard subtitles are useful for social platforms that don't accept separate subtitle files.
Best practices for quality subtitles
- Maximum 42 characters per line to fit on screen
- Maximum 2 lines per subtitle block
- Minimum duration: 1 second; recommended maximum: 7 seconds
- Reading speed: 17–20 words per minute for general audiences; 25 for frequent readers
- Sync to audio peaks, not grammatical sentence starts
Well-crafted subtitles improve accessibility, video SEO, and engagement on social platforms where 85% of video is consumed without sound.
Related conversions
Frequent conversions across the catalogue: