Video Processing Editing

# ❌ Replace audio without sync consideration
ffmpeg -i video.mp4 -i audio.mp3 \
  -map 0:v -map 1:a \
  -c:v copy -c:a copy \
  output.mp4

# Problems:
# - Audio duration ≠ video duration
# - No audio stretching/compression
# - Drift over time

# ✅ Adjust audio speed to match video duration

# Get durations
VIDEO_DUR=$(ffprobe -v error -show_entries format=duration \
  -of default=noprint_wrappers=1:nokey=1 video.mp4)
AUDIO_DUR=$(ffprobe -v error -show_entries format=duration \
  -of default=noprint_wrappers=1:nokey=1 audio.mp3)

# Calculate speed ratio
RATIO=$(echo "$VIDEO_DUR / $AUDIO_DUR" | bc -l)

# Stretch audio to match video (with pitch correction)
ffmpeg -i video.mp4 -i audio.mp3 \
  -filter_complex "[1:a]atempo=${RATIO}[a]" \
  -map 0:v -map "[a]" \
  -c:v copy -c:a aac -b:a 192k \
  output.mp4

# ✅ Sync audio with offset and trim

# Audio starts 0.5s late, trim to match video
ffmpeg -i video.mp4 -itsoffset 0.5 -i audio.mp3 \
  -map 0:v -map 1:a \
  -shortest \
  -c:v copy -c:a aac -b:a 192k \
  output.mp4

# -itsoffset: Delay audio by 0.5s
# -shortest: Trim to shortest stream

# ✅ Mix dialogue, music, effects with precise timing

ffmpeg -i video.mp4 -i dialogue.wav -i music.mp3 -i sfx.wav \
  -filter_complex "
    [1:a]adelay=0|0[dlg];
    [2:a]volume=0.3,adelay=500|500[mus];
    [3:a]adelay=1200|1200[sfx];
    [dlg][mus][sfx]amix=inputs=3:duration=first[a]
  " \
  -map 0:v -map "[a]" \
  -c:v copy -c:a aac -b:a 256k \
  output.mp4

# adelay: Precise millisecond timing
# amix: Mix multiple audio streams
# volume: Normalize levels

□ Verify video and audio durations match
□ Use -shortest to prevent excess audio
□ Apply adelay for precise timing offsets
□ Use atempo for speed adjustment (maintains pitch)
□ Set audio bitrate appropriately (128k-256k)
□ Test lip sync at beginning, middle, end

# ❌ Export everything at 4K 50 Mbps
ffmpeg -i input.mp4 \
  -c:v libx264 -b:v 50M -s 3840x2160 \
  -c:a aac -b:a 320k \
  output.mp4

# For Instagram story: 2 GB file, rejected (max 100 MB)
# For YouTube: Could use 10 Mbps and look identical
# For Twitter: Exceeds bitrate limits

# ✅ YouTube 1080p upload
ffmpeg -i input.mp4 \
  -c:v libx264 -preset slow -crf 18 \
  -s 1920x1080 -r 30 \
  -pix_fmt yuv420p \
  -color_primaries bt709 -color_trc bt709 -colorspace bt709 \
  -movflags +faststart \
  -c:a aac -b:a 192k -ar 48000 \
  youtube_1080p.mp4

# YouTube 4K upload
ffmpeg -i input.mp4 \
  -c:v libx264 -preset slow -crf 18 \
  -s 3840x2160 -r 60 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -c:a aac -b:a 256k -ar 48000 \
  youtube_4k.mp4

# ✅ Instagram Story (9:16, max 100 MB, 15s)
ffmpeg -i input.mp4 \
  -c:v libx264 -preset medium -crf 23 \
  -s 1080x1920 -r 30 -t 15 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -c:a aac -b:a 128k \
  instagram_story.mp4

# ✅ Instagram Reel (9:16, max 90s)
ffmpeg -i input.mp4 \
  -c:v libx264 -preset medium -crf 23 \
  -s 1080x1920 -r 30 -t 90 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -c:a aac -b:a 128k \
  instagram_reel.mp4

# ✅ Instagram Feed (1:1 or 4:5)
ffmpeg -i input.mp4 \
  -c:v libx264 -preset medium -crf 23 \
  -s 1080x1080 -r 30 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -c:a aac -b:a 128k \
  instagram_feed.mp4

# ✅ Twitter video (max 512 MB, 2:20)
ffmpeg -i input.mp4 \
  -c:v libx264 -preset medium -crf 23 \
  -s 1280x720 -r 30 -t 140 \
  -maxrate 5000k -bufsize 10000k \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -c:a aac -b:a 128k \
  twitter.mp4

# ✅ TikTok (9:16, max 287 MB, 10 min)
ffmpeg -i input.mp4 \
  -c:v libx264 -preset medium -crf 23 \
  -s 1080x1920 -r 30 -t 600 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -c:a aac -b:a 128k \
  tiktok.mp4

# ✅ Web optimized (fast load, broad compatibility)
ffmpeg -i input.mp4 \
  -c:v libx264 -preset medium -crf 23 \
  -s 1920x1080 -r 30 \
  -pix_fmt yuv420p \
  -profile:v baseline -level 3.0 \
  -movflags +faststart \
  -c:a aac -b:a 128k -ar 48000 \
  web.mp4

□ Use -movflags +faststart for web (progressive download)
□ Use -pix_fmt yuv420p for broad compatibility
□ Set -r 30 for most platforms (avoid variable framerate)
□ Use -preset slow for final exports (better quality)
□ Use -preset ultrafast for drafts
□ Apply -maxrate and -bufsize for streaming
□ Test playback on target platform before bulk export

□ Align cuts to keyframes (or two-pass seek)
□ Chain operations in single FFmpeg command
□ Normalize color spaces before concatenating
□ Verify audio/video sync (test at multiple points)
□ Use platform-specific export presets
□ Apply -movflags +faststart for web delivery
□ Set proper color metadata (bt709 for HD)
□ Test output file on target platform
□ Keep lossless intermediate files (ProRes, FFV1)
□ Use hardware acceleration for batch jobs (NVENC, VideoToolbox)