FFmpeg filter_complex effects, by example

Simple FFmpeg commands use -vf (a single linear chain). The moment you need multiple inputs or branching — a watermark, picture-in-picture, a split-and-recombine color grade — you graduate to filter_complex. It describes a directed graph of filters connected by named labels like [base] and [v].

Reading a filter graph

Two rules unlock the whole syntax. A comma chains filters on the same stream; a semicolon ends one branch and starts another. Labels in square brackets name the inputs and outputs so branches can reconnect:

[0:v]scale=1920:-2,setsar=1[base];
[1:v]format=rgba,
  colorchannelmixer=aa=0.6[ov];
[base][ov]overlay=(W-w)/2:(H-h)/2[v]

That graph scales the main clip to 1080p, makes the second input 60% opaque, and centers it as an overlay — a watermark or logo in three lines.

Overlay: watermarks and picture-in-picture

The overlay filter takes a base and an overlay stream and positions the second using x:y. The variables W/H (base size) and w/h (overlay size) make alignment easy:

• Top-left logo: overlay=20:20
• Bottom-right: overlay=W-w-20:H-h-20
• Centered: overlay=(W-w)/2:(H-h)/2

For picture-in-picture, scale the overlay down first: [1:v]scale=480:-1[pip];[0:v][pip]overlay=W-w-30:30.

Scale, pad, and crop

Resizing is the most common operation, and the most common source of squashed video. Always pair scale with setsar=1, and use -2 to keep dimensions even:

# fit 16:9 into a 1:1 square with padding
[0:v]scale=1080:-2,setsar=1,
  pad=1080:1080:0:(oh-ih)/2:black[v]

# crop a 1080x1080 center square
[0:v]crop=ih:ih:(iw-ih)/2:0[v]

Color correction and grading

FFmpeg ships a deep color toolkit. eq handles quick brightness/contrast/saturation; curves gives you per-channel control; colorchannelmixer and colorbalance let you push tones precisely:

[0:v]eq=contrast=1.1:saturation=1.15:brightness=0.02,
  curves=preset=lighter,
  colorbalance=rs=0.05:bs=-0.05[v]

Chroma key (green screen)

Composite a subject over a new background with chromakey, then overlay the result:

[1:v]chromakey=0x00FF00:0.30:0.10[key];
[0:v][key]overlay[v]

Chaining it all into one render

Real edits combine these. Here a clip is scaled, color-graded, watermarked, and handed off — a single reproducible command you can version-control:

ffmpeg -i main.mp4 -i logo.png -filter_complex "
  [0:v]scale=1920:-2,setsar=1,
    eq=contrast=1.08:saturation=1.1[base];
  [1:v]format=rgba,colorchannelmixer=aa=0.5[ov];
  [base][ov]overlay=W-w-30:H-h-30[v]
" -map "[v]" -map 0:a -c:a copy out.mp4

From filter graphs to a real timeline

FFmpegLab is built around exactly this idea: a visual timeline on top, the live filter_complex graph underneath. Build effects with controls, then open the generated script and tweak the graph by hand — every effect is a real, forkable FFmpeg filter chain. Combine it with xfade transitions and amix audio, all running privately and offline in the browser.