ffmpeg-expert

name	ffmpeg-expert
description	ffmpeg patterns for video pipelines — filters, audio, concat, GIF generation, codec settings. Covers Ken Burns, letterbox, fade, multi-act assembly, and macOS gotchas.

ffmpeg Expert

Mental Model

inputs (-i) → [filter graph: -vf / -af / -filter_complex] → codec flags → output

• Filters chain with , — applied in order
• Named splits use ; and [labels] — for complex graphs (split, overlay, amix)
• -an strips audio output; -vn strips video output
• -map 0:v:0 -map 1:a:0 — explicit stream selection when merging inputs

Quick Reference

I need to...	Use
Photo → video with Ken Burns zoom	→ references/filters.md
Letterbox any source to 1920×1080	→ references/filters.md
Fade video in/out	→ references/filters.md
Normalize fps + SAR before concat	→ references/filters.md
Loop a short song over a longer video	→ references/audio.md
Fade audio in/out	→ references/audio.md
Merge separate video + audio files	→ references/audio.md
Fix silent audio after concat	→ references/audio.md (sample rate)
Join pre-built segments	→ references/pipeline-patterns.md
Multi-act pipeline with per-act music	→ references/pipeline-patterns.md
Extract a frame from video	→ references/pipeline-patterns.md
Create a quality GIF	→ references/gif.md
Boomerang / speed-ramped GIF	→ references/gif.md

Must-Know Gotchas

Issue	Fix
bc aliased	Use /usr/bin/bc explicitly
BSD date rejects GNU flags	date -j -f '%Y-%m-%d' "YYYY-MM-DD" '+%B %Y'
HEIC not recognized	brew install libheif
Glob matches nothing → literal string passed	shopt -s nullglob at script top
fade=t=out:st= uses scientific notation	printf '%.6f' $(echo "$d - $f" | /usr/bin/bc)
Audio silent after concat	Mismatched sample rates — add -ar 48000 to all audio prep
DTS errors in concat	Mixed fps or SAR — normalize before joining
ffmpeg 8: -framerate on concat removed	Use duration directive in list file instead
Zoompan pixelates at zoom	Render at 2× resolution, downscale after (see filters.md)

Codec Defaults (Standard Pipeline)

-c:v libx264 -crf 18 -preset slow -pix_fmt yuv420p   # archival quality
-c:v libx264 -crf 26 -preset medium                   # shareable / preview
-c:a aac -b:a 192k -ar 48000                          # audio (always set -ar)
-movflags +faststart                                   # web streaming

CRF scale: 0 = lossless, 18 = high quality, 23 = default, 28 = small file, 51 = worst.

ffprobe — Get Duration

ffprobe -v quiet -show_entries format=duration -of csv=p=0 "$file"
# returns float seconds, e.g. 12.345678

References

• references/filters.md — Ken Burns/zoompan, letterbox, fade, fps/SAR normalization, drawtext
• references/audio.md — stream_loop, afade, sample rate, audio merge patterns
• references/pipeline-patterns.md — concat demuxer, photo→video, multi-act assembly
• references/gif.md — two-pass palette, boomerang, speed, size optimization