Viral Video Platform Specs

Viral Video Platform Specifications

Use this skill to choose export settings for TikTok, YouTube Shorts, Instagram Reels, Facebook Reels, Snapchat Spotlight, Twitter/X, Pinterest, LinkedIn, and mobile-browser playback. This SKILL is a lean orchestrator; detailed platform tables, commands, and recipes are preserved in references/platform-details-and-recipes.md.

Quick Reference

Universal Social Export Baseline

ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1,fps=30" \
  -c:v libx264 -preset medium -crf 22 -profile:v high -level 4.1 \
  -c:a aac -b:a 192k -ar 48000 -ac 2 \
  -pix_fmt yuv420p -movflags +faststart \
  output_social.mp4

Adjust loudness, duration, bitrate, and metadata per platform from the reference file.

Core Workflow

1. Verify ffmpeg -version; prefer current stable builds for security and codec fixes. 2. Identify target platform(s) and whether the video is native-app upload or mobile-browser playback. 3. Normalize to vertical 9:16 unless the platform or campaign calls for square/horizontal. 4. Use H.264/AAC for the broadest acceptance. Use VP9 only when intentionally targeting YouTube/WebM. 5. Apply platform loudness targets: TikTok/Reels often around -10 to -12 LUFS; YouTube around -14 LUFS; Facebook around -13 LUFS. 6. Keep -pix_fmt yuv420p and -movflags +faststart for compatibility. 7. Verify output with ffprobe before upload.

Key Gotchas

• All major social platforms re-encode uploads; high-quality H.264 is usually a better upload source than HEVC/AV1 for social delivery.
• For web/mobile-browser playback, profile/level, yuv420p, and faststart matter more than platform upload limits.
• Keep captions and UI out of unsafe top/bottom regions, especially lower 35% on Reels-style interfaces.
• Two-pass bitrate control is useful when a platform file-size ceiling is strict.

Reference Map

• references/platform-details-and-recipes.md - Full preserved reference: per-platform spec tables, FFmpeg presets, two-pass examples, multi-platform export script, file-size calculation, codec comparison, mobile-safe playback, color grading, text/caption readability, verification commands, sources.

Related Skills

• viral-video-animated-captions - CapCut-style caption generation
• viral-video-hook-templates - Hook patterns and retention tactics
• ffmpeg-animation-timing-reference - Timing, readability, sync, and platform pacing
• ffmpeg-command-syntax - Correct option placement

Extracted Detailed Reference

This file preserves the detailed material extracted from the original SKILL.md.

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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Viral Video Platform Specifications (2025-2026)

Complete reference for all major short-form video platforms with FFmpeg encoding presets.

Quick Reference Table

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TikTok Specifications

Technical Requirements (2025-2026)

Optimal Encoding Parameters (2025-2026)

Bitrate Recommendations (VBR):

• 24 fps: 4-6 Mbps
• 30 fps: 6-8.5 Mbps (sweet spot: 6-8 Mbps)
• 60 fps: 8-12 Mbps

CRF Values:

• CRF 21-23: Optimal quality/size balance
• Below CRF 21: Diminishing returns (TikTok recompresses)
• Above CRF 24: Noticeable quality loss on mobile

Preset Selection:

• fast: Quick encoding, good quality (recommended for batch)
• medium: Better compression (default)
• slow: Best quality (use for hero content)

FFmpeg Preset (Updated 2025-2026)

# TikTok optimized encoding - 2025-2026 specs
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1,fps=30" \
  -c:v libx264 -preset medium -crf 22 -profile:v high -level 4.1 \
  -x264-params "keyint=60:min-keyint=30:scenecut=0" \
  -c:a aac -b:a 192k -ar 44100 -ac 2 \
  -af "loudnorm=I=-11:TP=-1.5:LRA=11" \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -max_muxing_queue_size 1024 \
  -t 34 \
  output_tiktok.mp4

Two-Pass Encoding for Precise Bitrate Control

# Pass 1
ffmpeg -y -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset medium -b:v 7M -maxrate 8M -bufsize 16M \
  -profile:v high -level 4.1 -pass 1 -an -f null /dev/null

# Pass 2
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset medium -b:v 7M -maxrate 8M -bufsize 16M \
  -profile:v high -level 4.1 -pass 2 \
  -c:a aac -b:a 192k -ar 44100 \
  -af "loudnorm=I=-11:TP=-1.5:LRA=11" \
  -pix_fmt yuv420p -movflags +faststart \
  output_tiktok.mp4

Algorithm Insights (2025-2026)

• Hook Window: 1.3 seconds to capture attention
• Optimal Length: 21-34 seconds for highest completion
• Captions: 80% boost in engagement when visible
• Trending Audio: 88% say it helps discoverability
• Post Frequency: 1-3x daily for growth phase

---

YouTube Shorts Specifications

Technical Requirements (2025-2026)

Optimal Encoding Parameters (2025-2026)

Bitrate Recommendations (VBR):

• 1080p30: 8 Mbps (YouTube official recommendation)
• 1080p60: 12 Mbps

CRF Values:

• CRF 18-20: High quality (hero content, archival)
• CRF 20-22: Optimal quality/size (recommended)
• CRF 23+: Acceptable for less critical content

Preset Selection:

• slow: Best quality, longer encode (recommended for uploads)
• medium: Good balance for batch processing
• fast: Quick turnaround, slightly larger files

FFmpeg Preset - H.264 (Updated 2025-2026)

# YouTube Shorts H.264 encoding - maximum compatibility
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1,fps=30" \
  -c:v libx264 -preset slow -crf 20 -profile:v high -level 4.2 \
  -x264-params "keyint=60:min-keyint=30:scenecut=40" \
  -c:a aac -b:a 192k -ar 48000 -ac 2 \
  -af "loudnorm=I=-14:TP=-1.5:LRA=11" \
  -pix_fmt yuv420p \
  -colorspace bt709 -color_primaries bt709 -color_trc bt709 \
  -movflags +faststart \
  -max_muxing_queue_size 1024 \
  -t 59 \
  -metadata title="Your Shorts Title" \
  -metadata comment="#Shorts" \
  output_shorts.mp4

Two-Pass Encoding for Optimal Quality

# Pass 1 - Analysis
ffmpeg -y -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset slow -b:v 8M -profile:v high -level 4.2 \
  -pass 1 -an -f null /dev/null

# Pass 2 - Encode
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset slow -b:v 8M -profile:v high -level 4.2 \
  -pass 2 \
  -c:a aac -b:a 192k -ar 48000 \
  -af "loudnorm=I=-14:TP=-1.5:LRA=11" \
  -pix_fmt yuv420p -movflags +faststart \
  -metadata comment="#Shorts" \
  output_shorts.mp4

FFmpeg Preset (VP9 - Higher Quality)

# YouTube Shorts VP9 encoding (preferred by YouTube)
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1" \
  -c:v libvpx-vp9 -crf 25 -b:v 0 -deadline good -cpu-used 2 \
  -c:a libopus -b:a 192k -ar 48000 \
  -row-mt 1 \
  -t 59 \
  output_shorts.webm

Algorithm Insights (2025-2026)

• Completion Rate: 80-90% = algorithm boost
• Optimal Length: 50-60 seconds maximizes watch time
• First 3 Seconds: Critical for retention
• Consistency: Daily posting recommended for growth
• Thumbnail: Custom thumbnails increase CTR 30%+

---

Instagram Reels Specifications

Technical Requirements (2025-2026)

Optimal Encoding Parameters (2025-2026)

Bitrate Recommendations (VBR):

• Standard Quality: 3,500-5,000 kbps
• High Quality: 5,000-10,000 kbps (recommended for best results)

CRF Values:

• CRF 21-23: Optimal balance
• CRF 20: High quality for hero content
• CRF 24+: Avoid (visible compression on mobile)

Preset Selection:

• fast: Quick batch encoding
• medium: Recommended balance
• slow: Best quality (diminishing returns after Instagram recompression)

Safe Zones (2025-2026)

• Top safe zone: Keep text/graphics below top 14%
• Bottom safe zone: Avoid bottom 35% (UI overlays)
• Side safe zones: 6% margin on each side
• Text placement: Upper middle 2/3 of frame safest

FFmpeg Preset (Updated 2025-2026)

# Instagram Reels optimized encoding - high quality
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1,fps=30" \
  -c:v libx264 -preset medium -crf 22 -profile:v high -level 4.1 \
  -x264-params "keyint=60:min-keyint=30:scenecut=40" \
  -c:a aac -b:a 192k -ar 44100 -ac 2 \
  -af "loudnorm=I=-11:TP=-1.5:LRA=11" \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -t 30 \
  output_reels.mp4

Bitrate-Controlled Encoding

# Instagram Reels with precise bitrate (5-10 Mbps range)
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset medium -b:v 8M -maxrate 10M -bufsize 20M \
  -profile:v high -level 4.1 \
  -c:a aac -b:a 192k -ar 44100 \
  -af "loudnorm=I=-11:TP=-1.5:LRA=11" \
  -pix_fmt yuv420p -movflags +faststart \
  output_reels_bitrate.mp4

Algorithm Insights (2025-2026)

• Optimal Length: 7-15 seconds for casual, 15-30 for tutorial
• First 3 Seconds: Must hook immediately
• Trending Audio: Significant boost in reach
• Hashtags: 3-5 relevant hashtags optimal
• Post Time: When followers most active

---

Facebook Reels Specifications

Technical Requirements (2025-2026)

Optimal Encoding Parameters (2025-2026)

Bitrate Recommendations:

• 1080p H.264: 5-8 Mbps
• 4K H.264: 35-45 Mbps (up to 45 Mbps supported)
• Recommended for Reels: 6-10 Mbps at 1080p

CRF Values:

• CRF 20-22: High quality
• CRF 23: Good balance (recommended)
• CRF 24+: Acceptable for casual content

Safe Zones:

• Top: Leave 14% clear
• Bottom: Avoid 35% (UI elements)
• Sides: 6% margin each side

FFmpeg Preset (Updated 2025-2026)

# Facebook Reels optimized encoding - 2025-2026
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1,fps=30" \
  -c:v libx264 -preset medium -crf 22 -profile:v high -level 4.1 \
  -x264-params "keyint=60:min-keyint=30:scenecut=40" \
  -c:a aac -b:a 192k -ar 48000 -ac 2 \
  -af "loudnorm=I=-13:TP=-1:LRA=11" \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -t 30 \
  output_fb_reels.mp4

High-Quality Preset (Bitrate-Controlled)

# Facebook Reels - high quality with bitrate control
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset medium -b:v 8M -maxrate 10M -bufsize 20M \
  -profile:v high -level 4.1 \
  -c:a aac -b:a 192k -ar 48000 -ac 2 \
  -af "loudnorm=I=-13:TP=-1:LRA=11" \
  -pix_fmt yuv420p -movflags +faststart \
  output_fb_reels_hq.mp4

Algorithm Insights (2025-2026)

• Cross-Post: Instagram Reels can be shared to Facebook
• Original Content: Watermark-free content preferred
• Engagement: Comments boost reach significantly
• Optimal Length: 15-30 seconds

---

Snapchat Spotlight Specifications

Technical Requirements

FFmpeg Preset

# Snapchat Spotlight optimized encoding
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1,fps=30" \
  -c:v libx264 -preset fast -crf 24 -profile:v main -level 4.0 \
  -c:a aac -b:a 128k -ar 44100 -ac 2 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -fs 300M \
  -t 60 \
  output_spotlight.mp4

---

Twitter/X Video Specifications

Technical Requirements

FFmpeg Preset

# Twitter/X optimized encoding
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,setsar=1,fps=30" \
  -c:v libx264 -preset fast -crf 23 -profile:v high -level 4.1 \
  -c:a aac -b:a 128k -ar 44100 -ac 2 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -fs 512M \
  -t 140 \
  output_twitter.mp4

---

Multi-Platform Export Script

#!/bin/bash
# export_all_platforms.sh - Export video for all platforms at once

INPUT="$1"
BASENAME=$(basename "$INPUT" .mp4)

echo "Exporting $INPUT for all platforms..."

# TikTok
ffmpeg -i "$INPUT" \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a aac -b:a 128k -ar 44100 \
  -pix_fmt yuv420p -movflags +faststart \
  -t 60 \
  "${BASENAME}_tiktok.mp4" &

# YouTube Shorts
ffmpeg -i "$INPUT" \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k -ar 48000 \
  -pix_fmt yuv420p -movflags +faststart \
  -t 59 \
  "${BASENAME}_shorts.mp4" &

# Instagram Reels
ffmpeg -i "$INPUT" \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a aac -b:a 128k -ar 44100 \
  -pix_fmt yuv420p -movflags +faststart \
  -t 90 \
  "${BASENAME}_reels.mp4" &

# Snapchat Spotlight
ffmpeg -i "$INPUT" \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset fast -crf 24 \
  -c:a aac -b:a 128k -ar 44100 \
  -pix_fmt yuv420p -movflags +faststart \
  -fs 300M -t 60 \
  "${BASENAME}_spotlight.mp4" &

# Twitter/X
ffmpeg -i "$INPUT" \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black,fps=30" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a aac -b:a 128k -ar 44100 \
  -pix_fmt yuv420p -movflags +faststart \
  -t 140 \
  "${BASENAME}_twitter.mp4" &

wait
echo "All platform exports complete!"
ls -lh "${BASENAME}_*.mp4"

---

File Size Optimization

Calculate Target Bitrate for File Size

# Formula: bitrate = (target_size_MB * 8192) / duration_seconds - audio_bitrate

# Example: 50MB file, 60 seconds, 128kbps audio
# Video bitrate = (50 * 8192) / 60 - 128 = 6697 kbps

ffmpeg -i input.mp4 \
  -vf "scale=1080:1920" \
  -c:v libx264 -b:v 6500k -maxrate 7000k -bufsize 14000k \
  -c:a aac -b:a 128k \
  -pix_fmt yuv420p -movflags +faststart \
  output_sized.mp4

Two-Pass Encoding for Exact Size

# Pass 1
ffmpeg -y -i input.mp4 \
  -vf "scale=1080:1920" \
  -c:v libx264 -b:v 6500k -pass 1 -an -f null /dev/null

# Pass 2
ffmpeg -i input.mp4 \
  -vf "scale=1080:1920" \
  -c:v libx264 -b:v 6500k -pass 2 \
  -c:a aac -b:a 128k \
  -movflags +faststart \
  output_2pass.mp4

---

Platform Comparison: Algorithm Factors

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Verification Commands

# Verify platform compliance
verify_platform() {
    local file=$1
    echo "=== Checking: $file ==="
    ffprobe -v error -select_streams v:0 \
      -show_entries stream=width,height,codec_name,pix_fmt,r_frame_rate,bit_rate \
      -show_entries format=duration,size,bit_rate \
      -of default=noprint_wrappers=1 "$file"

    # File size in MB
    size_mb=$(ls -l "$file" | awk '{print $5/1024/1024}')
    echo "File Size: ${size_mb}MB"
}

verify_platform output_tiktok.mp4

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Codec Comparison for Short-Form Video (2025-2026)

H.264 vs H.265 vs AV1 Decision Matrix

Platform Codec Recommendations

Key Insight: All platforms re-encode uploads. Upload high-quality H.264 to give platform encoders the best source material. H.265/AV1 add encoding time with no benefit for social media.

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Color Grading for Viral Appeal (2025-2026)

Mobile-Optimized Color Parameters

Research-backed findings: Bold, saturated colors perform 2-3x better on mobile screens.

Viral Color Grading Presets

1. Bold & Eye-Popping (Maximum Engagement)

# High saturation, punchy contrast for maximum mobile impact
ffmpeg -i input.mp4 \
  -vf "eq=saturation=1.2:contrast=1.2:brightness=-0.02,unsharp=5:5:0.8" \
  -c:v libx264 -preset medium -crf 22 \
  output_bold.mp4

2. Orange & Teal (Cinematic Viral Look)

# Popular cinematic color grade - orange in highlights, teal in shadows
ffmpeg -i input.mp4 \
  -vf "\
    eq=contrast=1.15:saturation=1.1:brightness=-0.02,\
    colorbalance=rs=0.12:gs=-0.04:bs=-0.15:rm=0.08:gm=-0.02:bm=-0.08:rh=0.08:gh=-0.03:bh=-0.12,\
    curves=all='0/0.02 0.5/0.5 1/0.98',\
    unsharp=5:5:0.6\
  " \
  -c:v libx264 -preset medium -crf 22 \
  output_orange_teal.mp4

3. Vibrant Social Media Look

# Optimized for TikTok/Reels - saturated, sharp, mobile-friendly
ffmpeg -i input.mp4 \
  -vf "\
    eq=saturation=1.25:contrast=1.18:brightness=0.01:gamma=1.05,\
    colorbalance=rs=0.05:bs=-0.05,\
    unsharp=5:5:0.7\
  " \
  -c:v libx264 -preset medium -crf 22 \
  output_vibrant.mp4

4. Moody & Dramatic (Storytelling)

# Lower saturation, higher contrast, lifted blacks
ffmpeg -i input.mp4 \
  -vf "\
    eq=saturation=0.95:contrast=1.25:brightness=-0.03,\
    curves=all='0/0.05 0.5/0.48 1/0.95',\
    colorbalance=bs=0.08:bh=-0.05,\
    unsharp=5:5:0.5\
  " \
  -c:v libx264 -preset medium -crf 22 \
  output_moody.mp4

Using LUTs for Consistent Branding

# Apply a .cube LUT file for professional color grading
ffmpeg -i input.mp4 \
  -vf "lut3d=file=cinematic.cube,unsharp=5:5:0.6" \
  -c:v libx264 -preset medium -crf 22 \
  output_lut.mp4

Popular LUT sources:

• CapCut built-in LUTs (export as .cube)
• DaVinci Resolve free LUTs
• RocketStock free LUTs

Color Grading Best Practices

1. Test on mobile first: View on phone before posting 2. Avoid over-saturation: >1.3 saturation looks artificial 3. Check dark scenes: Compression artifacts most visible in shadows 4. Platform compression: Colors shift slightly after upload - compensate with +5% saturation 5. Consistent branding: Use same LUT across all videos for recognition

---

Text & Caption Parameters for Mobile Readability (2025-2026)

Font Size Guidelines (1080x1920 vertical)

Rule of thumb: For 1080x1920, minimum 48px for readability on all devices.

Safe Zones for Text Placement

┌─────────────────────┐
│   14% TOP MARGIN    │ ← Username, UI elements
├─────────────────────┤
│                     │
│   SAFE TEXT ZONE    │ ← Place all text here
│   (upper 2/3)       │
│                     │
├─────────────────────┤
│                     │
│  35% BOTTOM MARGIN  │ ← Captions, buttons, likes
└─────────────────────┘
    6%         6%
  ← margin  margin →

Best text placement: Upper-middle area (20-60% from top)

FFmpeg Text Overlay Parameters

Optimal Readability Settings

# Maximum mobile readability - white text, thick black outline
ffmpeg -i input.mp4 \
  -vf "drawtext=text='YOUR TEXT':fontsize=56:fontcolor=white:borderw=4:bordercolor=black:x=(w-tw)/2:y=h*0.15" \
  -c:v libx264 -preset medium -crf 22 \
  output_text.mp4

High-Contrast Combinations (Best Performing)

Text Animation for Engagement

# Fade-in text (2-second duration)
ffmpeg -i input.mp4 \
  -vf "drawtext=text='STOP SCROLLING':fontsize=72:fontcolor=yellow:borderw=5:bordercolor=black:x=(w-tw)/2:y=h*0.15:alpha='if(lt(t,1),t,1)':enable='between(t,0,2)'" \
  -c:v libx264 -preset medium -crf 22 \
  output_fade_text.mp4

Caption Best Practices (2025-2026)

Research findings:

• Captions increase engagement by 80% (TikTok)
• 94% of Reels watched on mobile with sound off
• Maximum 30 characters per line for readability
• Maximum 3 lines of text on screen simultaneously
• Minimum 2.3 seconds display time for 30-character line

Recommended caption style:

# Auto-caption burn-in (CapCut style)
-vf "subtitles=captions.srt:force_style='\
FontName=Arial Black,\
FontSize=52,\
PrimaryColour=&HFFFFFF,\
OutlineColour=&H000000,\
Outline=4,\
Shadow=0,\
Bold=1,\
Alignment=2,\
MarginV=250'"

---

Mobile Browser Playback Compatibility

While platform upload specs focus on what TikTok/YouTube/Instagram accept, mobile browser playback has its own requirements. Videos embedded in web apps, PWAs, or mobile browsers must meet stricter codec constraints than native app uploads.

H.264 Profile and Level Requirements

Recommendation: Use High Profile Level 4.0 for web-embedded video. It provides 15-25% bitrate savings over Baseline while maintaining near-universal mobile support on devices from 2015 onward.

The Faststart Requirement Explained

The moov atom is MP4's metadata container that tells the player where each frame is located, what codecs are used, and the video's structure. By default, FFmpeg writes it at the end of the file:

Default MP4:  [ftyp] [mdat (video data)] [moov (metadata)]
                                          ^ Player must download entire file
                                            before knowing how to play it

Faststart:    [ftyp] [moov (metadata)] [mdat (video data)]
                     ^ Player reads metadata first, starts playing immediately

On mobile networks (3G/4G/5G), without faststart:

• Video appears to hang while the full file downloads
• Users on slow connections see a black screen for seconds
• Safari may refuse to play the video entirely
• Progressive download is impossible

Always use `-movflags +faststart` for any video that will be played in a browser or streamed over HTTP.

Pixel Format Requirements

Mobile hardware video decoders only support yuv420p (4:2:0 chroma subsampling, 8-bit). Other formats will either:

• Fall back to slow software decoding (causing stuttering and battery drain)
• Display corrupted colors (green/purple tint)
• Fail to play entirely

# Check if a video uses a mobile-safe pixel format
ffprobe -v error -select_streams v:0 -show_entries stream=pix_fmt -of csv=p=0 INPUT

# SAFE:    yuv420p
# UNSAFE:  yuv422p, yuv444p, yuv420p10le (10-bit), gbrp, rgb24

Universal Mobile-Safe FFmpeg Preset

This preset guarantees playback on virtually all mobile browsers from 2015 onward:

# Universal mobile-safe encoding preset
ffmpeg -i input.mp4 \
  -c:v libx264 \
  -profile:v high -level 4.0 \
  -preset medium -crf 23 \
  -pix_fmt yuv420p \
  -c:a aac -profile:a aac_low \
  -b:a 128k -ar 44100 -ac 2 \
  -movflags +faststart \
  -max_muxing_queue_size 1024 \
  output_mobile_safe.mp4

For maximum compatibility (including Android 4.x and old WebViews):

# Maximum compatibility preset (older devices)
ffmpeg -i input.mp4 \
  -c:v libx264 \
  -profile:v main -level 3.1 \
  -preset medium -crf 23 \
  -pix_fmt yuv420p \
  -c:a aac -profile:a aac_low \
  -b:a 96k -ar 44100 -ac 2 \
  -vf "scale='min(1280,iw)':-2" \
  -movflags +faststart \
  output_max_compat.mp4

Mobile Codec Support Matrix

Common Mobile Gotchas

1. HEVC/H.265 is NOT universal: Only iOS Safari and some Android Chrome (with hardware decoder) support it. Firefox Android does not support HEVC at all. Always provide an H.264 fallback.

2. 10-bit color fails on most mobile: Videos encoded with yuv420p10le (common in HDR content) will not play on most mobile browsers. Convert to 8-bit yuv420p for web delivery.

3. Opus in MP4 containers: While Opus is efficient, it is poorly supported in MP4 containers on mobile. Use AAC-LC for MP4, or use Opus only in WebM containers.

4. Safari requires playsinline: Without the playsinline attribute in the HTML <video> tag, iOS Safari forces fullscreen playback. This is an HTML attribute, not an encoding issue, but it is the most common "why won't my video play inline on iPhone" complaint.

5. Audio-only autoplay is blocked: All mobile browsers block autoplay of videos with audible audio. Videos must be muted to autoplay. This cannot be worked around with encoding --- it is a browser policy.

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