SubRip Text Format (.srt)

Overview

SubRip Text (SRT) is a simple subtitle file format that originated from the DVD-ripping software SubRip. It is one of the most widely supported subtitle formats across media players, video editing software, and streaming platforms. SRT files contain subtitle text along with timing information that synchronizes the text with video playback.

Technical Specifications

Format Details

• File Extension: .srt
• MIME Type: text/plain
• Encoding: UTF-8 (recommended), ASCII, or other text encodings
• Structure: Plain text with specific formatting
• Line Endings: LF (Unix), CRLF (Windows), or CR (Mac)

SRT File Structure

1
00:00:01,500 --> 00:00:04,000
This is the first subtitle.

2
00:00:05,000 --> 00:00:08,500
This is the second subtitle
with multiple lines.

3
00:00:10,000 --> 00:00:12,000
<i>This subtitle has formatting.</i>

Timing Format

• Format: HH:MM:SS,mmm --> HH:MM:SS,mmm
• Hours: 00-99 (can exceed 24)
• Minutes: 00-59
• Seconds: 00-59
• Milliseconds: 000-999

History and Development

SubRip was developed in the early 2000s as DVD ripping software:

• 2000-2001: SubRip software created by unknown developers
• 2002: SRT format became widely adopted
• 2005: Format standardized by community usage
• 2010s: Became dominant subtitle format for streaming
• Present: Supported by virtually all media players

Common Use Cases

Basic Subtitle Creation

1
00:00:10,500 --> 00:00:13,000
Welcome to our presentation.

2
00:00:15,000 --> 00:00:18,500
Today we'll discuss the history
of subtitle formats.

3
00:00:20,000 --> 00:00:23,000
<b>Bold text</b> and <i>italic text</i>
are supported in many players.

Multi-language Subtitles

1
00:00:01,000 --> 00:00:03,000
Hello, world!

2
00:00:04,000 --> 00:00:06,000
How are you today?

3
00:00:07,000 --> 00:00:09,000
I'm fine, thank you.

Educational Content

1
00:00:00,000 --> 00:00:03,500
Chapter 1: Introduction to Physics

2
00:00:05,000 --> 00:00:08,000
Force equals mass times acceleration.
F = ma

3
00:00:10,000 --> 00:00:13,500
This fundamental equation describes
the relationship between these variables.

Tools and Software

Subtitle Editors

• Subtitle Edit: Free, comprehensive subtitle editor
• Aegisub: Advanced subtitle editor with timing tools
• Subtitle Workshop: Classic Windows subtitle editor
• VisualSubSync: Synchronization-focused editor

Video Players Supporting SRT

• VLC Media Player: Universal support
• MPC-HC: Windows media player
• Kodi: Media center software
• Plex: Media server platform
• Netflix, YouTube: Streaming platforms

Programming Libraries

# Python - pysrt library
import pysrt

# Read SRT file
subs = pysrt.open('subtitle.srt')

# Access subtitle properties
for sub in subs:
    print(f"{sub.index}: {sub.text}")
    print(f"Start: {sub.start}, End: {sub.end}")

# Create new subtitle
new_sub = pysrt.SubRipItem(
    index=1,
    start=pysrt.SubRipTime(0, 0, 1, 500),
    end=pysrt.SubRipTime(0, 0, 4, 0),
    text="Hello, World!"
)

// JavaScript - subtitle parsing
function parseSRT(content) {
    const blocks = content.trim().split('\n\n');
    return blocks.map(block => {
        const lines = block.split('\n');
        const index = parseInt(lines[0]);
        const [start, end] = lines[1].split(' --> ');
        const text = lines.slice(2).join('\n');
        
        return { index, start, end, text };
    });
}

Formatting and Styling

Basic HTML Tags

1
00:00:01,000 --> 00:00:03,000
<b>Bold text</b> for emphasis

2
00:00:04,000 --> 00:00:06,000
<i>Italic text</i> for thoughts

3
00:00:07,000 --> 00:00:09,000
<u>Underlined text</u> for importance

4
00:00:10,000 --> 00:00:12,000
<font color="red">Colored text</font>

Advanced Formatting

1
00:00:01,000 --> 00:00:03,000
<font face="Arial" size="18" color="yellow">
Custom font and color
</font>

2
00:00:05,000 --> 00:00:07,000
<b><i>Combined formatting</i></b>

3
00:00:08,000 --> 00:00:10,000
Line 1
Line 2 (manual line break)

Position and Alignment

1
00:00:01,000 --> 00:00:03,000
{\an8}Top-centered subtitle

2
00:00:04,000 --> 00:00:06,000
{\an1}Bottom-left subtitle

3
00:00:07,000 --> 00:00:09,000
{\an3}Bottom-right subtitle

Best Practices

Timing Guidelines

• Reading Speed: 150-180 words per minute
• Minimum Duration: 1 second for short text
• Maximum Duration: 7 seconds for long text
• Gap Between Subtitles: Minimum 125ms

Text Guidelines

• Line Length: Maximum 42 characters per line
• Lines per Subtitle: Maximum 2 lines
• Speaker Identification: Use dashes or colors
• Sound Effects: Use brackets [sound effect]

Quality Standards

1
00:00:01,000 --> 00:00:03,500
Keep subtitles concise
and easy to read.

2
00:00:04,000 --> 00:00:06,500
Break lines at logical points,
not in the middle of phrases.

3
00:00:07,000 --> 00:00:09,000
[Background music playing]

4
00:00:10,000 --> 00:00:12,500
- Speaker 1: Hello there!
- Speaker 2: Hi!

Conversion and Processing

Converting from Other Formats

# Convert ASS to SRT
import pysrt
import ass

# Read ASS file
with open('subtitle.ass', 'r', encoding='utf-8') as f:
    ass_content = ass.parse(f)

# Convert to SRT
srt_subs = pysrt.SubRipFile()
for event in ass_content.events:
    srt_sub = pysrt.SubRipItem(
        index=len(srt_subs) + 1,
        start=pysrt.SubRipTime.from_ordinal(event.start),
        end=pysrt.SubRipTime.from_ordinal(event.end),
        text=event.text
    )
    srt_subs.append(srt_sub)

srt_subs.save('output.srt')

Batch Processing

# Convert multiple files using ffmpeg
for file in *.mkv; do
    ffmpeg -i "$file" -map 0:s:0 "${file%.mkv}.srt"
done

# Extract subtitles from video
ffmpeg -i video.mp4 -map 0:s:0 -c:s srt subtitle.srt

Synchronization Tools

# Adjust timing (shift all subtitles)
subs = pysrt.open('subtitle.srt')
subs.shift(seconds=2)  # Delay by 2 seconds
subs.save('subtitle_adjusted.srt')

# Scale timing (speed up/slow down)
subs.shift(ratio=1.1)  # 10% faster

Validation and Quality Control

Common Issues

• Overlapping subtitles
• Too-fast reading speed
• Inconsistent formatting
• Encoding problems
• Timing drift

Validation Script

def validate_srt(filename):
    subs = pysrt.open(filename)
    issues = []
    
    for i, sub in enumerate(subs):
        # Check duration
        duration = sub.end - sub.start
        if duration.ordinal < 1000:  # Less than 1 second
            issues.append(f"Subtitle {sub.index}: Too short")
        
        # Check overlap with next subtitle
        if i < len(subs) - 1:
            next_sub = subs[i + 1]
            if sub.end > next_sub.start:
                issues.append(f"Subtitle {sub.index}: Overlaps with next")
        
        # Check line length
        lines = sub.text.split('\n')
        for line in lines:
            if len(line) > 42:
                issues.append(f"Subtitle {sub.index}: Line too long")
    
    return issues

Security Considerations

File Safety

• SRT files are plain text (generally safe)
• Check encoding to prevent character injection
• Validate content in media applications
• Be cautious with user-uploaded subtitle files

Content Filtering

import re

def sanitize_srt_text(text):
    # Remove potentially harmful HTML tags
    allowed_tags = ['b', 'i', 'u', 'font']
    # Basic sanitization logic
    return re.sub(r'<(?!/?({})\b)[^>]*>'.format('|'.join(allowed_tags)), '', text)

Platform-Specific Considerations

Streaming Services

• Netflix: Supports SRT with specific guidelines
• YouTube: Auto-converts to internal format
• Amazon Prime: Accepts SRT for user uploads
• Vimeo: Direct SRT upload support

Media Players

• VLC: Full SRT support including styling
• Windows Media Player: Basic SRT support
• QuickTime: Limited SRT support
• Mobile Players: Variable support for formatting

The SRT format remains the most universally compatible subtitle format, making it the preferred choice for content creators, educators, and media distributors worldwide due to its simplicity and widespread support.