video-post-production

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Video post-production rules: audio mastering, color, captions, platform export. Use when: 'add music', 'add voiceover', 'export for tiktok', 'add captions', 'color grade', 'audio levels', 'master audio', 'export settings', 'platform requirements'. Covers FFmpeg patterns, audio chain, subtitle standards, and platform-specific export configs. Do NOT use to generate or animate the video frames/scenes in code (use remotion-production-guide), to write the script (use video-narrative-arc), or to evaluate script quality (use script-evaluator); this is the finishing stage applied to an already-rendered video.

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Video Post-Production Guide

Rules and FFmpeg patterns for finishing videos: audio mastering, captions, color, and platform-specific export.

Audio Rules

Volume Levels (dB)

Track	Level	Notes
Voiceover	-12 to -10 dB	Primary audio, clear and upfront
Music (under VO)	-32 to -24 dB	Background, should not compete
Music (solo, no VO)	-16 to -12 dB	Can be louder when alone
Sound effects	-18 to -14 dB	Accent, not distraction
Silence floor	-60 dB	True silence feels unnatural, keep room tone

Music Selection by BPM

Mood	BPM Range	Use Case
Calm, reflective	60-80	Luxury brands, testimonials
Confident, steady	80-100	Corporate, explainers
Moderate energy	100-120	Product demos, features
Energetic	120-140	Launch videos, social ads
High energy	140+	Montage, fast-cut sequences

Rule: Match music tempo to edit pace. Cut on beats for professional feel.

Audio Mastering Chain (FFmpeg)

# Full mastering chain: highpass + EQ + compression + loudness
ffmpeg -i input.mp4 -af "
  highpass=f=80,
  equalizer=f=3000:t=q:w=1.5:g=3,
  acompressor=threshold=-20dB:ratio=4:attack=5:release=50,
  loudnorm=I=-16:TP=-1.5:LRA=11
" -c:v copy output.mp4

Free Music/SFX Libraries

Mixkit (mixkit.co) - royalty-free, no attribution
Pixabay Audio (pixabay.com/music) - free, Pixabay license
Freesound (freesound.org) - CC licensed, varies
YouTube Audio Library - free for YouTube content

Caption / Subtitle Rules

Standards

Parameter	Value
Max characters per line	32-42
Max 2 lines simultaneously	Always
Display duration	1.5-7 seconds per caption
Min display	1.5 seconds (even for short text)
Font size	48-72px (for 1080p)
Font	Sans-serif, bold weight
Position	Bottom center, 10% from bottom edge
Background	Semi-transparent black (#000000AA)

Burn-in Captions (FFmpeg)

# Basic caption burn-in
ffmpeg -i input.mp4 -vf "subtitles=subs.srt:force_style='FontSize=24,FontName=Arial,Bold=1,PrimaryColour=&HFFFFFF,OutlineColour=&H000000,Outline=2,MarginV=40'" output.mp4

# Word-by-word highlight (requires ASS format)
ffmpeg -i input.mp4 -vf "ass=styled_subs.ass" output.mp4

Color Correction

Quick Presets (FFmpeg)

# Warm punch (indoor/talking head)
ffmpeg -i input.mp4 -vf "eq=contrast=1.1:brightness=0.02:saturation=1.15,colorbalance=rs=0.05:gs=-0.02:bs=-0.05" output.mp4

# Cool tech (product/SaaS)
ffmpeg -i input.mp4 -vf "eq=contrast=1.05:saturation=0.95,colorbalance=rs=-0.03:gs=0.01:bs=0.05" output.mp4

# High contrast B&W
ffmpeg -i input.mp4 -vf "hue=s=0,eq=contrast=1.3:brightness=0.03" output.mp4

Platform Export Configs

YouTube (16:9)

ffmpeg -i input.mp4 \
  -c:v libx264 -preset slow -crf 18 -pix_fmt yuv420p \
  -c:a aac -b:a 192k -ar 48000 \
  -movflags +faststart \
  youtube_output.mp4

TikTok / Instagram Reels (9:16)

# Resize landscape to vertical with blur background
ffmpeg -i input_16x9.mp4 \
  -filter_complex "[0:v]scale=1080:1920:force_original_aspect_ratio=decrease,pad=1080:1920:(ow-iw)/2:(oh-ih)/2:black[fg];[0:v]scale=1080:1920,boxblur=20:20[bg];[bg][fg]overlay=(W-w)/2:(H-h)/2" \
  -c:v libx264 -preset fast -crf 23 -pix_fmt yuv420p \
  -c:a aac -b:a 128k \
  tiktok_output.mp4

# Native vertical render from Remotion
npx remotion render src/index.ts Comp out/vertical.mp4 --width 1080 --height 1920

Instagram Square (1:1)

# Center crop to square
ffmpeg -i input_16x9.mp4 \
  -vf "crop=ih:ih:(iw-ih)/2:0,scale=1080:1080" \
  -c:v libx264 -crf 23 -pix_fmt yuv420p \
  -c:a aac -b:a 128k \
  square_output.mp4

Common FFmpeg Operations

Trim

# Fast trim (keyframe-based, instant)
ffmpeg -ss 00:00:05 -i input.mp4 -t 15 -c copy trimmed.mp4

# Frame-accurate trim (re-encodes)
ffmpeg -i input.mp4 -ss 00:00:05 -t 15 -c:v libx264 -crf 18 trimmed.mp4

Concatenate

# Create file list
echo "file 'scene1.mp4'" > list.txt
echo "file 'scene2.mp4'" >> list.txt
echo "file 'scene3.mp4'" >> list.txt

# Lossless concat (same codec/resolution)
ffmpeg -f concat -safe 0 -i list.txt -c copy output.mp4

# Re-encoded concat (different sources)
ffmpeg -f concat -safe 0 -i list.txt -c:v libx264 -crf 18 output.mp4

Add Background Music

# Music at -24dB under existing audio
ffmpeg -i video.mp4 -i music.mp3 \
  -filter_complex "[1:a]volume=-24dB[music];[0:a][music]amix=inputs=2:duration=first" \
  -c:v copy output.mp4

Speed Change

# 2x speed (with audio pitch correction)
ffmpeg -i input.mp4 -vf "setpts=0.5*PTS" -af "atempo=2.0" fast.mp4

# 0.5x slow motion
ffmpeg -i input.mp4 -vf "setpts=2.0*PTS" -af "atempo=0.5" slow.mp4

GIF Creation

# High quality GIF with palette
ffmpeg -i input.mp4 -vf "fps=15,scale=480:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" output.gif

Quality Checklist (Post-Render)

Before publishing, verify:

No black frames at start/end
Audio levels consistent (no sudden jumps)
Captions readable on mobile (test at 50% zoom)
Colors look correct on both dark and light screens
File size within platform limits
Aspect ratio correct for target platform
First frame is visually interesting (it becomes the thumbnail)
Last frame has clear CTA visible for 2+ seconds

Gotchas

Always use -pix_fmt yuv420p - some players can't handle other formats
Always use -movflags +faststart for web playback (moves metadata to file start)
FFmpeg -ss BEFORE -i = fast seek (keyframe). AFTER -i = accurate (slower)
aac codec needs -strict experimental on some FFmpeg versions
Complex filter graphs: keep each step simple. Claude makes subtle errors in long chains
Test on mobile FIRST - most video is watched on phones