viral-video-animated-captions

CRITICAL GUIDELINES

Windows File Path Requirements

MANDATORY: Always Use Backslashes on Windows for File Paths

When using Edit or Write tools on Windows, you MUST use backslashes (\) in file paths, NOT forward slashes (/).

Documentation Guidelines

NEVER create new documentation files unless explicitly requested by the user.

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CapCut-Style Animated Captions (2025-2026)

Why Animated Captions Matter

• 80% engagement boost when captions are present
• 85% of social video is watched without sound
• Animated word highlighting increases retention by 25-40%
• CapCut-style captions are now expected by viewers

---

Quick Reference

Style	Effect	Best For
Word Pop	Words bounce in one at a time	High energy, Gen Z
Highlight Sweep	Color sweeps across words	Professional, educational
Karaoke	Words light up with audio timing	Music, voiceover
Typewriter	Characters appear sequentially	Storytelling, dramatic
Scale Pulse	Words pulse larger on appear	Emphasis, key points

---

Caption Workflow Overview

Standard Workflow

1. Generate transcript with word-level timestamps (Whisper)
2. Convert to ASS format with animation styles
3. Burn captions into video with FFmpeg

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Step 1: Generate Word-Level Timestamps

Using Whisper (FFmpeg 8.0+)

# Generate JSON with word-level timestamps
ffmpeg -i input.mp4 -vn \
  -af "whisper=model=ggml-base.bin:language=auto:format=json" \
  transcript.json

Using whisper.cpp Directly (More Control)

# Generate word-level JSON
whisper.cpp/main -m ggml-base.bin -f audio.wav -ojf -ml 1

# Output: audio.wav.json with word timings

Using OpenAI Whisper API

import whisper

model = whisper.load_model("base")
result = model.transcribe("audio.mp3", word_timestamps=True)

# Access word-level timing
for segment in result["segments"]:
    for word in segment["words"]:
        print(f"{word['word']}: {word['start']:.2f} - {word['end']:.2f}")

---

Step 2: Create Animated ASS Subtitles

ASS File Structure

[Script Info]
ScriptType: v4.00+
PlayResX: 1080
PlayResY: 1920
WrapStyle: 0

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Arial Black,72,&H00FFFFFF,&H000000FF,&H00000000,&H80000000,1,0,0,0,100,100,0,0,1,4,2,2,10,10,200,1
Style: Highlight,Arial Black,72,&H0000FFFF,&H000000FF,&H00000000,&H80000000,1,0,0,0,100,100,0,0,1,4,2,2,10,10,200,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text

Style 1: Word Pop (CapCut Default)

Each word pops in with a scale animation.

[V4+ Styles]
Style: WordPop,Montserrat,80,&H00FFFFFF,&H00FFFF00,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,5,0,2,10,10,250,1

[Events]
; Word "This" pops in at 0.0s
Dialogue: 0,0:00:00.00,0:00:00.50,WordPop,,0,0,0,,{\fscx50\fscy50\t(0,100,\fscx110\fscy110)\t(100,200,\fscx100\fscy100)}This
; Word "is" pops in at 0.3s
Dialogue: 0,0:00:00.30,0:00:00.80,WordPop,,0,0,0,,{\fscx50\fscy50\t(0,100,\fscx110\fscy110)\t(100,200,\fscx100\fscy100)}is
; Word "AMAZING" pops in with emphasis at 0.5s
Dialogue: 0,0:00:00.50,0:00:01.20,WordPop,,0,0,0,,{\c&H00FFFF&\fscx50\fscy50\t(0,100,\fscx120\fscy120)\t(100,250,\fscx100\fscy100)}AMAZING

Style 2: Highlight Sweep

Words appear white, then highlight yellow as spoken.

[V4+ Styles]
Style: Sweep,Arial Black,72,&H00FFFFFF,&H0000FFFF,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,4,0,2,10,10,250,1

[Events]
; Full sentence appears, words highlight in sequence
Dialogue: 0,0:00:00.00,0:00:02.00,Sweep,,0,0,0,,{\k20}This {\k15}is {\k25}how {\k20}you {\k30}do {\k20}it

Style 3: Karaoke (Music/Voiceover)

Progressive color fill across each word.

[V4+ Styles]
Style: Karaoke,Impact,80,&H00FFFFFF,&H0000FFFF,&H00000000,&H00000000,1,0,0,0,100,100,0,0,1,5,0,2,10,10,250,1

[Events]
; Karaoke timing (values in centiseconds)
Dialogue: 0,0:00:00.00,0:00:03.00,Karaoke,,0,0,0,,{\kf50}This {\kf40}is {\kf60}the {\kf45}secret {\kf70}formula

Style 4: Typewriter Effect

Characters appear one at a time.

[V4+ Styles]
Style: Typewriter,Courier New,64,&H00FFFFFF,&H00FFFFFF,&H00000000,&H80000000,0,0,0,0,100,100,0,0,1,3,0,2,10,10,250,1

[Events]
; Each character has its own timing
Dialogue: 0,0:00:00.00,0:00:00.10,Typewriter,,0,0,0,,T
Dialogue: 0,0:00:00.10,0:00:00.20,Typewriter,,0,0,0,,Th
Dialogue: 0,0:00:00.20,0:00:00.30,Typewriter,,0,0,0,,Thi
Dialogue: 0,0:00:00.30,0:00:00.40,Typewriter,,0,0,0,,This
; ... continue for each character

Style 5: Bounce In

Words bounce from below with overshoot.

[V4+ Styles]
Style: Bounce,Arial Black,76,&H00FFFFFF,&H0000FFFF,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,4,0,2,10,10,250,1

[Events]
; Word bounces up from bottom
Dialogue: 0,0:00:00.00,0:00:00.80,Bounce,,0,0,0,,{\move(540,1200,540,960)\t(0,150,\fscx110\fscy110)\t(150,300,\fscx95\fscy95)\t(300,400,\fscx100\fscy100)}Word

---

Caption Generation Scripts

Python Script: JSON to Animated ASS

#!/usr/bin/env python3
"""
Convert Whisper JSON transcript to animated ASS subtitles.
Usage: python json_to_ass.py transcript.json output.ass [style]
Styles: pop, sweep, karaoke, bounce
"""

import json
import sys

def format_time(seconds):
    """Convert seconds to ASS timestamp format (H:MM:SS.cc)"""
    h = int(seconds // 3600)
    m = int((seconds % 3600) // 60)
    s = seconds % 60
    return f"{h}:{m:02d}:{s:05.2f}"

def generate_pop_style(words):
    """Generate word-pop animation (CapCut default style)"""
    events = []
    for word_data in words:
        word = word_data['word'].strip()
        start = word_data['start']
        end = word_data['end']

        # Pop animation: scale from 50% to 110% to 100%
        # NOTE: ASS \t() animation tags use MILLISECONDS (not centiseconds!)
        # \t(0,80,...) = 0-80ms scale up, \t(80,180,...) = 80-180ms scale down
        effect = r"{\fscx50\fscy50\t(0,80,\fscx115\fscy115)\t(80,180,\fscx100\fscy100)}"

        events.append(
            f"Dialogue: 0,{format_time(start)},{format_time(end)},WordPop,,0,0,0,,{effect}{word}"
        )
    return events

def generate_sweep_style(segments):
    """Generate highlight sweep animation"""
    events = []
    for segment in segments:
        words = segment.get('words', [])
        if not words:
            continue

        start_time = words[0]['start']
        end_time = words[-1]['end']

        # Build karaoke timing string
        # NOTE: ASS karaoke \k tags use CENTISECONDS (multiply seconds by 100)
        karaoke_text = ""
        for i, word_data in enumerate(words):
            word = word_data['word'].strip()
            # Convert seconds to centiseconds: 0.5s * 100 = 50 centiseconds = {\k50}
            duration = int((word_data['end'] - word_data['start']) * 100)
            karaoke_text += f"{{\\k{duration}}}{word} "

        events.append(
            f"Dialogue: 0,{format_time(start_time)},{format_time(end_time)},Sweep,,0,0,0,,{karaoke_text.strip()}"
        )
    return events

def generate_karaoke_style(segments):
    """Generate karaoke-fill animation"""
    events = []
    for segment in segments:
        words = segment.get('words', [])
        if not words:
            continue

        start_time = words[0]['start']
        end_time = words[-1]['end']

        # Build karaoke fill timing
        karaoke_text = ""
        for word_data in words:
            word = word_data['word'].strip()
            duration = int((word_data['end'] - word_data['start']) * 100)
            karaoke_text += f"{{\\kf{duration}}}{word} "

        events.append(
            f"Dialogue: 0,{format_time(start_time)},{format_time(end_time)},Karaoke,,0,0,0,,{karaoke_text.strip()}"
        )
    return events

def generate_bounce_style(words):
    """Generate bounce-in animation"""
    events = []
    for word_data in words:
        word = word_data['word'].strip()
        start = word_data['start']
        end = word_data['end']

        # Bounce from below with overshoot
        # NOTE: ASS \t() and \move() use MILLISECONDS
        # 0-120ms: scale up, 120-200ms: overshoot, 200-280ms: settle (total 280ms bounce)
        effect = r"{\move(540,1100,540,960)\t(0,120,\fscx115\fscy115)\t(120,200,\fscx95\fscy95)\t(200,280,\fscx100\fscy100)}"

        events.append(
            f"Dialogue: 0,{format_time(start)},{format_time(end)},Bounce,,0,0,0,,{effect}{word}"
        )
    return events

def create_ass_file(transcript_path, output_path, style='pop'):
    """Create ASS file from Whisper JSON transcript"""

    with open(transcript_path, 'r') as f:
        data = json.load(f)

    # ASS header
    header = """[Script Info]
ScriptType: v4.00+
PlayResX: 1080
PlayResY: 1920
WrapStyle: 0
Title: Animated Captions

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: WordPop,Arial Black,80,&H00FFFFFF,&H0000FFFF,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,5,0,2,10,10,250,1
Style: Sweep,Arial Black,72,&H00FFFFFF,&H0000FFFF,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,4,0,2,10,10,250,1
Style: Karaoke,Impact,80,&H00FFFFFF,&H0000FFFF,&H00000000,&H00000000,1,0,0,0,100,100,0,0,1,5,0,2,10,10,250,1
Style: Bounce,Arial Black,76,&H00FFFFFF,&H0000FFFF,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,4,0,2,10,10,250,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
"""

    # Extract all words from segments
    all_words = []
    segments = data.get('segments', [])
    for segment in segments:
        words = segment.get('words', [])
        all_words.extend(words)

    # Generate events based on style
    if style == 'pop':
        events = generate_pop_style(all_words)
    elif style == 'sweep':
        events = generate_sweep_style(segments)
    elif style == 'karaoke':
        events = generate_karaoke_style(segments)
    elif style == 'bounce':
        events = generate_bounce_style(all_words)
    else:
        events = generate_pop_style(all_words)

    # Write ASS file
    with open(output_path, 'w', encoding='utf-8') as f:
        f.write(header)
        f.write('\n'.join(events))

    print(f"Created {output_path} with {len(events)} caption events ({style} style)")

if __name__ == "__main__":
    if len(sys.argv) < 3:
        print("Usage: python json_to_ass.py transcript.json output.ass [style]")
        print("Styles: pop, sweep, karaoke, bounce")
        sys.exit(1)

    transcript = sys.argv[1]
    output = sys.argv[2]
    style = sys.argv[3] if len(sys.argv) > 3 else 'pop'

    create_ass_file(transcript, output, style)

Bash Script: Full Caption Pipeline

#!/bin/bash
# animated_captions.sh - Full pipeline for animated captions
# Usage: ./animated_captions.sh input.mp4 [style]

INPUT="$1"
STYLE="${2:-pop}"  # Default to 'pop' style
OUTPUT="${INPUT%.mp4}_captioned.mp4"

echo "=== Animated Caption Pipeline ==="
echo "Input: $INPUT"
echo "Style: $STYLE"

# Step 1: Extract audio
echo "[1/4] Extracting audio..."
ffmpeg -y -i "$INPUT" -vn -acodec pcm_s16le -ar 16000 -ac 1 audio_temp.wav

# Step 2: Generate transcript with Whisper
echo "[2/4] Generating transcript with Whisper..."
# Using FFmpeg's built-in Whisper (FFmpeg 8.0+)
ffmpeg -y -i audio_temp.wav \
  -af "whisper=model=ggml-base.bin:language=auto:destination=transcript.json:format=json" \
  -f null -

# Step 3: Convert to animated ASS
echo "[3/4] Creating animated ASS subtitles ($STYLE style)..."
python3 json_to_ass.py transcript.json captions.ass "$STYLE"

# Step 4: Burn subtitles into video
echo "[4/4] Burning captions into video..."
ffmpeg -y -i "$INPUT" \
  -vf "ass=captions.ass" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a copy \
  "$OUTPUT"

# Cleanup
rm -f audio_temp.wav transcript.json

echo "=== Complete! ==="
echo "Output: $OUTPUT"

---

FFmpeg Caption Presets

Burn ASS Captions

# Standard ASS burn
ffmpeg -i input.mp4 \
  -vf "ass=captions.ass" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a copy \
  output_captioned.mp4

# With custom fonts directory
ffmpeg -i input.mp4 \
  -vf "ass=captions.ass:fontsdir=/path/to/fonts" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a copy \
  output_captioned.mp4

Real-Time Caption Overlay (Whisper + Drawtext)

# Live captions from Whisper directly overlaid
ffmpeg -i input.mp4 \
  -af "whisper=model=ggml-base.bin:language=en" \
  -vf "drawtext=text='%{metadata\:lavfi.whisper.text}':fontsize=56:fontcolor=white:borderw=4:bordercolor=black:x=(w-tw)/2:y=h-th-200:box=1:boxcolor=black@0.4:boxborderw=10" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a aac -b:a 128k \
  output_live_captions.mp4

---

Caption Style Presets

TikTok Viral Style

Style: TikTokViral,Arial Black,84,&H00FFFFFF,&H0000FFFF,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,6,0,2,10,10,300,1

• Font: Arial Black (bold, readable)
• Size: 84 (large for mobile)
• Colors: White text, yellow highlight
• Position: Lower third (MarginV=300)

YouTube Shorts Professional

Style: ShortsPro,Montserrat,72,&H00FFFFFF,&H00FFFFFF,&H00333333,&H80000000,1,0,0,0,100,100,0,0,1,4,2,2,10,10,280,1

• Font: Montserrat (modern, clean)
• Size: 72
• Colors: White with gray outline
• Shadow: Yes (professional look)

Instagram Reels Trendy

Style: ReelsTrend,Impact,80,&H00FFFFFF,&H00FF00FF,&H00000000,&H00000000,1,0,0,0,100,100,2,0,1,5,0,2,10,10,260,1

• Font: Impact
• Size: 80
• Colors: White text, magenta highlight
• Letter spacing: 2 (spread out)

Mr. Beast Style (High Energy)

Style: MrBeast,Impact,96,&H0000FFFF,&H000000FF,&H00000000,&H00000000,1,0,0,0,110,110,0,0,1,8,0,2,10,10,200,1

• Font: Impact
• Size: 96 (HUGE)
• Colors: Yellow text, red highlight
• Scale: 110% (extra impact)

---

Color Schemes for Different Content

High Energy / Gaming

Primary: &H0000FFFF (Yellow)
Highlight: &H000000FF (Red)
Outline: &H00000000 (Black)

Professional / Educational

Primary: &H00FFFFFF (White)
Highlight: &H00FFD700 (Gold)
Outline: &H00333333 (Dark Gray)

Lifestyle / Aesthetic

Primary: &H00FFFFFF (White)
Highlight: &H00FFC0CB (Pink)
Outline: &H00000000 (Black)

Comedy / Casual

Primary: &H00FFFFFF (White)
Highlight: &H0000FF00 (Green)
Outline: &H00000000 (Black)

---

Emoji Integration

Adding Emojis to Captions

; Emoji in ASS subtitles (requires emoji font)
Dialogue: 0,0:00:01.00,0:00:02.00,Default,,0,0,0,,This is FIRE 🔥

; Using emoji font explicitly
Dialogue: 0,0:00:01.00,0:00:02.00,Default,,0,0,0,,{\fnSegoe UI Emoji}🔥{\fnArial Black} AMAZING

Common Viral Emojis

🔥 - Fire (excitement, trending)
💀 - Skull (dying laughing)
😱 - Shocked (reactions)
✅ - Checkmark (lists, confirmations)
❌ - X mark (wrong/avoid)
💯 - 100 (emphasis, agreement)
👀 - Eyes (attention, looking)
🚨 - Alert (important, breaking)

---

Platform-Specific Caption Guidelines

Platform	Font Size	Position	Max Words/Screen	Animation
TikTok	80-96	Center/Lower	3-5 words	Fast, punchy
YouTube Shorts	72-84	Lower third	4-6 words	Smooth, readable
Instagram Reels	76-88	Center	3-5 words	Trendy, stylish
Facebook Reels	72-80	Lower third	5-7 words	Clear, accessible

---

Troubleshooting

Captions Not Showing

# Verify ASS file is valid
ffmpeg -i captions.ass -f null -

# Check font availability
fc-list | grep -i "arial"

Timing Issues

# Shift all captions by 0.5 seconds
ffmpeg -itsoffset 0.5 -i captions.ass shifted.ass

Wrong Position on 9:16

# Adjust MarginV in ASS style for vertical video
# MarginV=250-350 is typical for 1920px height

---

Advanced Animation Parameters for Viral Content

Spring Physics Formulas for Bounce Animations

Spring physics create natural, organic motion that feels more engaging than linear animations.

Core Spring Formula

Position = equilibrium + amplitude * e^(-damping*t) * sin(frequency*t)

Practical Spring Parameters

Parameter	Value Range	Effect	Recommended
Damping	0.5-5.0	How quickly bounce settles	2.5-3.5 for captions
Frequency	5-20 rad/s	Bounce speed	12-15 for punchy feel
Amplitude	10-50 pixels	Bounce height	20-30 for text

Spring Bounce Examples

; Subtle spring bounce (0.4s total)
; Scale: 50% → 115% → 95% → 100% (overshoot then settle)
{\fscx50\fscy50\t(0,120,\fscx115\fscy115)\t(120,240,\fscx95\fscy95)\t(240,400,\fscx100\fscy100)}Word

; Aggressive spring bounce (0.6s total)
; Scale: 40% → 130% → 90% → 105% → 100% (multiple oscillations)
{\fscx40\fscy40\t(0,100,\fscx130\fscy130)\t(100,250,\fscx90\fscy90)\t(250,450,\fscx105\fscy105)\t(450,600,\fscx100\fscy100)}IMPACT

; Position spring bounce (from below)
{\move(540,1300,540,960,0,150)\t(0,150,\fscy115)\t(150,300,\fscy95)\t(300,450,\fscy100)}Bounce

Mathematical Reasoning

The overshoot (115% → 95%) simulates spring physics where momentum carries the object past equilibrium before settling. The exponential decay factor e^(-damping*t) ensures the oscillation amplitude decreases over time, creating a natural settling effect.

Damping ratio formula:

• ζ = damping / (2 * sqrt(stiffness * mass))
• Under-damped (0 < ζ < 1): Bouncy, overshoots (viral content)
• Critically damped (ζ = 1): No overshoot, fastest settle (professional)
• Over-damped (ζ > 1): Slow, sluggish (avoid)

Easing Functions for Natural Motion

Cubic Bezier Curve Approximations

ASS doesn't support cubic-bezier directly, but we can approximate with multi-stage \t() transforms:

Ease-Out (Deceleration - elements appearing):

; Approximates cubic-bezier(0, 0, 0.2, 1)
; Fast start (70% in first 40%), slow finish
{\fscx50\fscy50\t(0,120,\fscx85\fscy85)\t(120,200,\fscx95\fscy95)\t(200,300,\fscx100\fscy100)}EaseOut

Ease-In (Acceleration - elements disappearing):

; Approximates cubic-bezier(0.8, 0, 1, 1)
; Slow start, fast finish
{\fscx100\fscy100\t(0,100,\fscx95\fscy95)\t(100,180,\fscx85\fscy85)\t(180,300,\fscx50\fscy50)}EaseIn

Ease-In-Out (Smooth both ends):

; Approximates cubic-bezier(0.4, 0, 0.2, 1) - Material Design standard
{\fscx50\fscy50\t(0,80,\fscx70\fscy70)\t(80,220,\fscx90\fscy90)\t(220,300,\fscx100\fscy100)}EaseInOut

Elastic Easing (Rubber Band Effect)

; Elastic overshoot - great for emphasis
; Formula: sin((t*10 - 0.75)*PI) * e^(-t*5)
{\fscx50\fscy50\t(0,80,\fscx140\fscy140)\t(80,180,\fscx85\fscy85)\t(180,320,\fscx110\fscy110)\t(320,500,\fscx100\fscy100)}ELASTIC

Mathematical basis: sin((x*10 - 0.75)*(2*PI/3)) * pow(2, -10*x) where x = normalized time (0-1)

Optimal Timing Parameters by Platform (2026 Research)

Based on 2026 viral content analysis and WCAG accessibility guidelines:

TikTok Timing Profile

Parameter	Value	Reasoning
Caption appear speed	80-150ms	Fast platform, snappy expectations
Word dwell time	250-400ms	Minimum: 250ms, longer for emphasis
Bounce duration	180-300ms	Quick, energetic feel
Shake amplitude	3-8 pixels	Readable but noticeable
Max words/screen	3-5 words	Mobile-first, quick reading
Animation delay between words	50-100ms	Rapid succession

YouTube Shorts Timing Profile

Parameter	Value	Reasoning
Caption appear speed	150-250ms	Slightly more polished than TikTok
Word dwell time	400-600ms	Better readability on larger screens
Bounce duration	250-400ms	Smooth, professional feel
Shake amplitude	2-5 pixels	Subtle, not distracting
Max words/screen	4-6 words	Comfortable reading chunk
Animation delay between words	80-150ms	Measured pacing

Instagram Reels Timing Profile

Parameter	Value	Reasoning
Caption appear speed	150-250ms	Aesthetic, stylish timing
Word dwell time	300-500ms	Visual-first platform
Bounce duration	200-350ms	Trendy, polished
Shake amplitude	4-10 pixels	More dramatic for aesthetics
Max words/screen	3-5 words	Short, impactful phrases
Animation delay between words	100-180ms	Rhythmic pacing

Shake/Tremor Effects with Readability Limits

Maximum Readable Shake Amplitudes

Research shows text readability degrades rapidly with excessive motion:

Font Size	Max Horizontal Shake	Max Vertical Shake	Frequency Limit
64-72px	8-10 pixels	6-8 pixels	8-12 Hz
76-84px	10-15 pixels	8-12 pixels	8-12 Hz
88-96px	15-20 pixels	12-16 pixels	6-10 Hz

Rule of thumb: Shake amplitude should not exceed 15% of font size for readability.

Shake Animation Examples

; Subtle shake (emphasis without distraction)
; Horizontal: ±5px, 12Hz oscillation, 0.3s duration
{\pos(540,960)\t(0,50,\pos(545,960))\t(50,100,\pos(535,960))\t(100,150,\pos(543,960))\t(150,200,\pos(537,960))\t(200,250,\pos(541,960))\t(250,300,\pos(540,960))}Text

; Impact shake (decay pattern)
; Amplitude decreases: 10px → 6px → 3px → 0px
{\pos(540,960)\t(0,60,\pos(550,960))\t(60,120,\pos(534,960))\t(120,200,\pos(543,960))\t(200,300,\pos(540,960))}BOOM

FFmpeg drawtext shake (continuous):

# Subtle shake: x offset = 5 * sin(t*40) (40 rad/s ≈ 6.4 Hz)
-vf "drawtext=text='LIVE':fontsize=80:fontcolor=red:\
     x='(w-tw)/2+5*sin(t*40)':\
     y='(h-th)/2+3*sin(t*40+1.57)'"

# Decaying shake (impact effect): amplitude decreases exponentially
-vf "drawtext=text='BOOM':fontsize=120:fontcolor=white:\
     x='(w-tw)/2+15*exp(-t*3)*sin(t*50)':\
     y='(h-th)/2+10*exp(-t*3)*cos(t*50)'"

Pulse/Breathing Effects

Scale Pulse (Heartbeat Effect)

; Continuous pulse: 100% ↔ 105% every 1 second
; Use with looping for sustained emphasis
{\t(0,500,\fscx105\fscy105)\t(500,1000,\fscx100\fscy100)}Word

FFmpeg drawtext pulse:

# Sine wave pulse: fontsize oscillates 72 ± 8 pixels at 2 Hz
-vf "drawtext=text='SUBSCRIBE':fontsize='72+8*sin(t*12.56)':\
     fontcolor=yellow:x=(w-tw)/2:y=h-150"
# 12.56 rad/s = 2π rad/cycle × 2 cycles/s = 2 Hz

Mathematical reasoning: sin(2πf*t) where f = frequency in Hz

• 1 Hz (slow): sin(6.28*t) = sin(t*6.28)
• 2 Hz (medium): sin(12.56*t) = sin(t*12.56)
• 3 Hz (fast): sin(18.85*t) = sin(t*18.85)

Per-Character vs Per-Word Timing

Character-Level Animation (Typewriter)

Optimal timing: 30-80ms per character for comfortable reading

# Typewriter timing formula
chars_per_second = 1000 / ms_per_char
# 50ms per char = 20 chars/second (comfortable)
# 30ms per char = 33 chars/second (fast, energetic)
# 80ms per char = 12.5 chars/second (dramatic, slow)

ASS character reveal (manual):

; Each character appears with 50ms delay
Dialogue: 0,0:00:00.00,0:00:00.05,Style,,0,0,0,,H
Dialogue: 0,0:00:00.05,0:00:00.10,Style,,0,0,0,,He
Dialogue: 0,0:00:00.10,0:00:00.15,Style,,0,0,0,,Hel
Dialogue: 0,0:00:00.15,0:00:00.20,Style,,0,0,0,,Hell
Dialogue: 0,0:00:00.20,0:00:01.00,Style,,0,0,0,,Hello

Word-Level Animation (CapCut Style)

Optimal timing: 200-400ms per word with 50-150ms gap between words

# Word animation timing formula
def word_timing(word_count, platform='tiktok'):
    timings = {
        'tiktok': {'appear': 120, 'dwell': 300, 'gap': 80},
        'youtube': {'appear': 180, 'dwell': 450, 'gap': 120},
        'instagram': {'appear': 150, 'dwell': 350, 'gap': 100}
    }
    t = timings[platform]

    total_duration = 0
    for i in range(word_count):
        total_duration += t['appear'] + t['dwell'] + t['gap']

    return total_duration  # in milliseconds

Accessibility Considerations

WCAG 2.2 Animation Guidelines

1. Maximum flash frequency: 3 flashes per second (avoid seizures)

   • Do NOT use animations faster than 333ms cycle time

2. Motion reduction: Provide prefers-reduced-motion alternative

   • For web: CSS @media (prefers-reduced-motion: reduce)
   • For video: Export both animated and static caption versions

3. Minimum caption duration: 1.5 seconds (WCAG Level AA)

   • Even fast platforms should respect this for accessibility

4. Maximum reading speed: 200 WPM (3.3 words/second)

   • Formula: duration >= (word_count / 3.3) + animation_time

Safe Animation Parameters

Animation Type	Safe Range	Accessibility Limit	Notes
Shake amplitude	0-15px	10px max	Higher risks illegibility
Shake frequency	2-10 Hz	8 Hz max	Above 10 Hz may trigger seizures
Pulse magnitude	100-110%	108% max	Excessive scale distracts
Flash duration	100-300ms	Must be < 333ms	3 flash/sec limit

Mathematical Formulas Reference

Oscillation Functions

Sine wave (smooth oscillation):

y = amplitude * sin(frequency * t + phase)

Example: 5*sin(t*12) = 5 pixel amplitude, 12 rad/s ≈ 1.9 Hz

Cosine wave (90° phase shift from sine):

y = amplitude * cos(frequency * t)

Use cosine for perpendicular motion (e.g., circular paths)

Exponential decay (settling):

y = initial * e^(-decay_rate * t)

Example: 10*exp(-t*3) = 10 pixels decaying with rate 3/sec

Damped oscillation (spring bounce):

y = amplitude * e^(-damping*t) * sin(frequency*t)

Example: 20*exp(-t*2.5)*sin(t*12) = spring with damping 2.5, frequency 12 rad/s

Bezier Curve Approximation

Cubic bezier (p0, p1, p2, p3) can be approximated with 3-stage linear transitions:

Standard ease-out (0, 0, 0.2, 1):

• Stage 1 (0-40%): 50% of total change
• Stage 2 (40-70%): 35% of total change
• Stage 3 (70-100%): 15% of total change

Standard ease-in (0.8, 0, 1, 1):

• Stage 1 (0-30%): 15% of total change
• Stage 2 (30-60%): 35% of total change
• Stage 3 (60-100%): 50% of total change

Platform Caption Accessibility Summary (2026)

Based on research from OpusClip, Instagram, and YouTube best practices:

Critical Requirements

1. Silent viewing optimization: 85% of social video watched without sound
2. Contrast ratio: Minimum 4.5:1 (WCAG Level AA)
3. Font choice: Sans-serif (Arial, Helvetica, Montserrat)
4. Burned-in preferred: Platform auto-captions often inaccurate
5. Word-level timing: Higher engagement than full-sentence captions

Recommended Safe Zone (Mobile)

Top margin: 150-200px (avoid notch, status bar)
Bottom margin: 200-300px (avoid UI, captions, CTA)
Side margins: 40-60px (safe for all aspect ratios)

ASS safe zone positioning:

; 1080x1920 vertical video safe zone
Style: SafeZone,Arial Black,80,&H00FFFFFF,&H0000FFFF,&H00000000,&H40000000,1,0,0,0,100,100,0,0,1,5,0,2,50,50,280,1
;                                                                                           ↑  ↑   ↑
;                                                                                        Left Right Bottom
;                                                                                        50px 50px 280px

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Sources

This skill was enhanced with research from:

• Instagram Reels Caption Best Practices 2026
• YouTube Shorts Caption Best Practices 2026
• Short-Form Video Mastery Guide 2026
• FFmpeg Drawtext Animation Exploration
• Spring Physics for UI Animations
• ASS Karaoke Documentation
• WCAG Animation Accessibility

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Related Skills

• ffmpeg-captions-subtitles - Full caption system
• ffmpeg-karaoke-animated-text - Advanced karaoke effects
• ffmpeg-animation-timing-reference - Timing formulas and parameters
• viral-video-platform-specs - Platform requirements
• viral-video-hook-templates - Hook patterns