Video Post-Production Guide

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