CRITICAL GUIDELINES

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YouTube Shorts Viral Video Creator

Purpose

Transform any video into a YouTube Shorts-optimized viral format with:

• 9:16 vertical aspect ratio (1080x1920)
• Auto-generated captions with engaging styling
• Optimal duration (50-60 seconds for max retention)
• Thumbnail extraction for custom cover selection
• YouTube-compliant encoding (VP9/H.264, HDR support)
• Loop-friendly endings for increased watch time

Quick Start

Basic Shorts Conversion

# Simple conversion to YouTube Shorts format
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 libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k -ar 48000 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -t 59 \
  output_shorts.mp4

Complete YouTube Shorts Workflow

Step 1: Analyze Input

# Check source video properties
ffprobe -v quiet -print_format json -show_format -show_streams input.mp4

Key metrics:

• Duration (Shorts max: 60s, optimal: 50-60s)
• Resolution (need 9:16 vertical)
• Audio quality (YouTube supports higher bitrate than TikTok)

Step 2: Create 9:16 Vertical Format

From Horizontal (16:9) Video - Smart Cropping

# Option A: Intelligent center crop with face detection zone
ffmpeg -i horizontal.mp4 \
  -vf "crop=ih*9/16:ih:(iw-ih*9/16)/2:0,scale=1080:1920" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k \
  -pix_fmt yuv420p -movflags +faststart \
  output_shorts.mp4

# Option B: Cinematic letterbox with gradient bars
ffmpeg -i horizontal.mp4 \
  -filter_complex "
    [0:v]scale=1080:-2[main];
    color=c=black:s=1080x1920:d=1[bg];
    [bg][main]overlay=0:(H-h)/2:shortest=1,
    drawbox=x=0:y=0:w=1080:h=300:c=black@0.7:t=fill,
    drawbox=x=0:y=1620:w=1080:h=300:c=black@0.7:t=fill
  " \
  -c:v libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k \
  -pix_fmt yuv420p -movflags +faststart \
  output_shorts.mp4

# Option C: Picture-in-picture with blurred background
ffmpeg -i horizontal.mp4 \
  -filter_complex "
    [0:v]scale=1080:1920:force_original_aspect_ratio=increase,crop=1080:1920,boxblur=25:25[bg];
    [0:v]scale=1080:-2[fg];
    [bg][fg]overlay=0:(H-h)/2
  " \
  -c:v libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k \
  -pix_fmt yuv420p -movflags +faststart \
  output_shorts.mp4

From Long-Form YouTube Video (Clip Extraction)

# Extract viral clip from longer video
ffmpeg -i long_video.mp4 \
  -ss 00:05:30 -t 00:00:58 \
  -vf "crop=ih*9/16:ih,scale=1080:1920" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k \
  -pix_fmt yuv420p -movflags +faststart \
  shorts_clip.mp4

Step 3: Optimize Duration for Algorithm

YouTube Shorts algorithm favors videos that are watched to completion.

# Trim to optimal 50-58 second range
ffmpeg -i input.mp4 \
  -ss 00:00:00 -t 00:00:55 \
  -c:v libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k \
  -pix_fmt yuv420p -movflags +faststart \
  output_optimal_length.mp4

Step 4: Add Captions for Retention

Auto-Generate with Whisper (FFmpeg 8.0+)

# Generate captions (FFmpeg 8.0+ with Whisper)
ffmpeg -i input.mp4 -vn \
  -af "whisper=model=ggml-medium.bin:language=auto:format=srt" \
  captions.srt

# Burn captions with YouTube-optimized style
ffmpeg -i shorts_base.mp4 \
  -vf "subtitles=captions.srt:force_style='FontName=Montserrat,FontSize=52,PrimaryColour=&HFFFFFF,OutlineColour=&H000000,BackColour=&H40000000,Outline=3,Shadow=2,Bold=1,Alignment=2,MarginV=250'" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a copy \
  shorts_with_captions.mp4

Caption Styles for Different Content Types

# Gaming/Energetic style
-vf "subtitles=caps.srt:force_style='FontName=Impact,FontSize=56,PrimaryColour=&H00FFFF,OutlineColour=&H000000,Outline=4,Bold=1,Alignment=2,MarginV=200'"

# Educational/Professional style
-vf "subtitles=caps.srt:force_style='FontName=Roboto,FontSize=44,PrimaryColour=&HFFFFFF,OutlineColour=&H333333,Outline=2,Shadow=1,Alignment=2,MarginV=280'"

# Storytelling/Dramatic style
-vf "subtitles=caps.srt:force_style='FontName=Georgia,FontSize=48,PrimaryColour=&HFFD700,OutlineColour=&H000000,Outline=3,Italic=1,Alignment=2,MarginV=240'"

Step 5: Add Hook Elements

Opening Text Hook (First 2 Seconds)

# Curiosity gap hook
ffmpeg -i input.mp4 \
  -vf "drawtext=text='This changed everything...':fontsize=60:fontcolor=white:borderw=4:bordercolor=black:x=(w-tw)/2:y=h*0.15:enable='between(t,0,2.5)',drawtext=text='Watch till the end':fontsize=36:fontcolor=yellow:borderw=2:bordercolor=black:x=(w-tw)/2:y=h*0.22:enable='between(t,0,2.5)'" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a copy \
  output_with_hook.mp4

Visual Pattern Interrupt

# Flash/brightness pulse at start
ffmpeg -i input.mp4 \
  -vf "eq=brightness=0.1*sin(t*12)*between(t,0,0.5)" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a copy \
  output_flash_hook.mp4

Step 6: Create Loop-Friendly Ending

# Crossfade last 1 second with first 1 second for smooth loop
ffmpeg -i input.mp4 \
  -filter_complex "
    [0:v]trim=0:1,setpts=PTS-STARTPTS[start];
    [0:v]trim=54:55,setpts=PTS-STARTPTS[end];
    [end][start]xfade=transition=fade:duration=0.5:offset=0.5[loop];
    [0:v]trim=0:54,setpts=PTS-STARTPTS[main];
    [main][loop]concat=n=2:v=1:a=0
  " \
  -c:v libx264 -preset fast -crf 22 \
  output_looped.mp4

Step 7: Extract Thumbnails

# Extract multiple thumbnail options
ffmpeg -i output_shorts.mp4 -vf "select='eq(n,0)+eq(n,60)+eq(n,120)+eq(n,180)'" -vsync vfr thumbnail_%02d.jpg

# Extract at specific timestamp with text overlay
ffmpeg -i output_shorts.mp4 -ss 00:00:15 -vframes 1 \
  -vf "drawtext=text='YOUR TITLE':fontsize=72:fontcolor=white:borderw=5:bordercolor=black:x=(w-tw)/2:y=h*0.4" \
  thumbnail_with_text.jpg

# High-quality thumbnail
ffmpeg -i output_shorts.mp4 -ss 00:00:10 -vframes 1 \
  -q:v 2 \
  thumbnail_hq.jpg

Step 8: Encode for Quality

Standard Quality (H.264)

ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black" \
  -c:v libx264 -preset slow -crf 20 \
  -c:a aac -b:a 192k -ar 48000 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  output_hq.mp4

Premium Quality (VP9 - YouTube's Preferred)

ffmpeg -i input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black" \
  -c:v libvpx-vp9 -crf 25 -b:v 0 -deadline good \
  -c:a libopus -b:a 192k \
  -row-mt 1 \
  output_vp9.webm

HDR Content (If Source is HDR)

ffmpeg -i hdr_input.mp4 \
  -vf "scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black" \
  -c:v libx265 -preset slow -crf 22 \
  -tag:v hvc1 \
  -color_primaries bt2020 -color_trc smpte2084 -colorspace bt2020nc \
  -c:a aac -b:a 192k \
  output_hdr.mp4

Complete One-Command Preset

# Full YouTube Shorts optimization pipeline
ffmpeg -i input.mp4 \
  -filter_complex "
    [0:v]scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black[v1];
    [v1]drawtext=text='YOUR HOOK':fontsize=56:fontcolor=white:borderw=4:bordercolor=black:x=(w-tw)/2:y=h*0.12:enable='between(t,0,2.5)'[v2];
    [0:a]loudnorm=I=-14:TP=-1.5:LRA=11[a]
  " \
  -map "[v2]" -map "[a]" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a aac -b:a 192k -ar 48000 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -t 59 \
  -metadata title="Your Shorts Title" \
  -metadata comment="#Shorts" \
  output_shorts_final.mp4

YouTube Shorts Technical Requirements (2025-2026)

Specification	Requirement	Optimal Value
Aspect Ratio	9:16 (vertical)	Required for Shorts shelf
Resolution	1080x1920 (recommended)	1080x1920 (limited to 1080p playback)
Video Codec	H.264, VP9, HEVC	H.264 (compatibility), VP9 (quality)
Audio Codec	AAC, Opus	AAC-LC (most compatible)
Audio Bitrate	192-384 kbps	192 kbps minimum, 384 kbps YouTube recommendation
Audio Loudness	-13 to -15 LUFS	-14 LUFS (YouTube normalizes to this)
True Peak	-1 to -3 dB	-1.5 dBTP recommended
Frame Rate	24-60 fps	30 fps (upload at source frame rate)
Bitrate (1080p30)	8 Mbps	8 Mbps (YouTube official)
Bitrate (1080p60)	12 Mbps	12 Mbps
CRF (H.264)	18-23	CRF 20 (high quality), CRF 22 (standard)
Preset	slow, medium, fast	slow (best quality for uploads)
Max File Size	256 GB	Practical: 20-100 MB for Shorts
Max Duration	60 seconds (HARD LIMIT)	Strict enforcement
Optimal Duration	50-60 seconds	Maximizes watch time metric
Min Duration	~15 seconds recommended	Shorter = harder to rank
Pixel Format	yuv420p (SDR)	yuv420p10le for HDR
Color Space	Rec.709 (SDR)	Rec.2100 for HDR only
Audio Sample Rate	48000 Hz preferred	YouTube production standard

Algorithm Optimization Tips

Duration Strategy

Length	Performance
15-30s	Good for simple concepts, high completion
30-45s	Balanced, good for tutorials
50-60s	Algorithm favorite, max watch time

Retention Techniques

# Add progress bar (increases completion rate)
ffmpeg -i input.mp4 \
  -vf "drawbox=x=0:y=1900:w='(t/60)*1080':h=20:c=red:t=fill" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a copy \
  output_with_progress.mp4

# Subtle continuous zoom - 0.15%/sec for YouTube (larger screens need more movement)
# YouTube Shorts viewers often watch on TVs, requiring 1.5x TikTok's zoom rate
ffmpeg -i input.mp4 \
  -vf "zoompan=z='1+0.0015*t':d=1:x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':s=1080x1920" \
  -c:v libx264 -preset fast -crf 22 \
  output_slow_zoom.mp4

Audio Optimization (2025-2026 Research)

YouTube Shorts Audio Targets:

• Loudness: -13 to -15 LUFS (YouTube normalizes to -14 LUFS)
• True Peak: -1 to -3 dBTP (recommended: -1.5 dBTP)
• Strategy: Upload at -14 LUFS for minimal platform processing

# Normalize audio for YouTube Shorts - -14 LUFS target
ffmpeg -i input.mp4 \
  -af "loudnorm=I=-14:TP=-1.5:LRA=11" \
  -c:v copy \
  output_normalized_shorts.mp4

# Voice clarity with YouTube-optimized loudness
ffmpeg -i input.mp4 \
  -af "highpass=f=80,lowpass=f=12000,compand=attacks=0:points=-80/-900|-45/-15|-27/-9|0/-7|20/-7:gain=3,loudnorm=I=-14:TP=-1.5" \
  -c:v copy \
  output_voice_optimized.mp4

End Screen Call-to-Action

# Add subscribe reminder in last 5 seconds
ffmpeg -i input.mp4 \
  -vf "drawtext=text='SUBSCRIBE':fontsize=48:fontcolor=red:borderw=3:bordercolor=white:x=(w-tw)/2:y=h*0.85:enable='gte(t,55)'" \
  -c:v libx264 -preset fast -crf 22 \
  -c:a copy \
  output_with_cta.mp4

Batch Processing for Content Repurposing

#!/bin/bash
# batch_shorts.sh - Convert multiple clips to Shorts format

for input in *.mp4; do
    output="shorts_${input}"

    # Get duration
    duration=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "$input")

    # Cap at 59 seconds
    if (( $(echo "$duration > 59" | bc -l) )); then
        trim="-t 59"
    else
        trim=""
    fi

    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 \
      -pix_fmt yuv420p -movflags +faststart \
      $trim \
      "$output"

    # Extract thumbnail
    ffmpeg -i "$output" -ss 00:00:05 -vframes 1 "thumb_${input%.mp4}.jpg"
done

Output Verification

# Verify Shorts compliance
ffprobe -v error -select_streams v:0 \
  -show_entries stream=width,height,codec_name,pix_fmt,r_frame_rate \
  -show_entries format=duration \
  -of csv=p=0 output_shorts.mp4

# Expected: 1080,1920,h264,yuv420p,30/1 and duration < 60

# Check file integrity
ffmpeg -v error -i output_shorts.mp4 -f null - && echo "Valid" || echo "Error"

Related Skills

• viral-video-platform-specs - All platform upload requirements
• viral-video-hook-templates - 10 proven hook patterns
• viral-video-animated-captions - CapCut-style word highlighting
• ffmpeg-captions-subtitles - Full caption system