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)
bash# 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)
bash# 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)
bash# 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)
bashffmpeg -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)
bash# 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)
bash# 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
bash# 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
bash# 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
bash# 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
bash# 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
bash# 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 +faststartfor web playback (moves metadata to file start) - FFmpeg
-ssBEFORE-i= fast seek (keyframe). AFTER-i= accurate (slower) aaccodec needs-strict experimentalon 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
