Ffmpeg Synth

Ffmpeg Synth

Context: $ARGUMENTS

Quick start

• SMPTE HD bars + 1 kHz tone (10 s 1080p30): -f lavfi -i smptehdbars=... -f lavfi -i sine=... → Step 3, recipe A
• testsrc2 moving pattern + counter: -f lavfi -i testsrc2=size=1280x720:rate=30 → Step 3, recipe B
• Solid color fill: -f lavfi -i color=c=red:size=1280x720:rate=30:duration=5 → Step 3, recipe C
• Gradient background: -f lavfi -i "gradients=s=1920x1080:c0=red:c1=blue:speed=0.01" → Step 3, recipe D
• Mandelbrot zoom: -f lavfi -i mandelbrot=size=1920x1080:rate=30 -t 10 → Step 3, recipe E
• Legacy PAL 75 % bars: -f lavfi -i pal75bars=size=720x576:rate=25 -t 10 → Step 3, recipe F
• Silent stereo audio track: -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=48000 -t 10 → Step 3, recipe G
• White / pink / brown noise: -f lavfi -i anoisesrc=color=pink:duration=10:amplitude=0.3 → Step 3, recipe H
• Sine sweep tone: -f lavfi -i "sine=frequency=440:beep_factor=4:duration=10" → Step 3, recipe I
• Identity Hald CLUT PNG (for LUT authoring): -f lavfi -i haldclutsrc=level=8 -frames:v 1 hald.png → Step 3, recipe J
• colorchecker 24-patch PNG: -f lavfi -i colorchecker -frames:v 1 colorchecker.png → Step 3, recipe K

When to use

• Pipeline integration tests that must not depend on external media files.
• Broadcast calibration — SMPTE bars + -20 dBFS 1 kHz tone for line-up.
• ABX audio listening tests (white / pink / brown noise as reference).
• Encoder stress testing — high-entropy rgbtestsrc / mandelbrot / testsrc2.
• Overlay backgrounds — solid color or gradients as a plate for drawtext/overlay.
• LUT authoring — identity haldclutsrc round-tripped through a grading tool.
• Placeholder silence track to marry onto a video-only source.
• Monitor calibration / gamut checks — pal100bars, smptehdbars, rgbtestsrc.
• Not a playback preview tool — for interactive filter tweaks use ffmpeg-playback.
• For writing the synthetic video through a filter chain (drawtext overlay, LUT), see ffmpeg-video-filter and ffmpeg-lut-grade.

Step 1 — Pick a source

All synthetic sources live inside libavfilter and are addressed via the lavfi input format. Choose by category:

Probe whether your ffmpeg supports a given source before committing to it:

ffmpeg -hide_banner -sources lavfi 2>/dev/null   # list lavfi devices (sometimes empty)
ffmpeg -hide_banner -h filter=smptehdbars        # dump the options for one source
ffmpeg -hide_banner -filters | grep -E "smpte|testsrc|colorchecker"

Step 2 — Build the lavfi input

Every lavfi source is an -f lavfi -i <expression> pair. The expression is filter syntax, not a file path:

-f lavfi -i "SOURCE=key1=val1:key2=val2:..."

Always quote the expression (colons and commas need protection in most shells). Key knobs:

• size=WxH (or s=WxH) — output frame size. Some sources have defaults (smptebars→320x240), some don't — set it explicitly for anything HD or above.
• rate=N (or r=N) — video framerate, fps.
• duration=N — source-level duration, seconds (or HH:MM:SS.ms). Leave it off → source runs forever until -t or EOF.
• sample_rate=N (or sr=N) — audio sample rate, Hz.
• channel_layout=mono|stereo|5.1 — audio layout (not channels=2 for most sources; see gotchas).
• pixel_format=yuv420p|yuv422p|rgb24|… — some sources accept it; use format= filter otherwise.
• c=<colorname> / color=<…> — solid-color sources accept CSS/HTML names, 0xRRGGBB, #RRGGBB, random.

Compose video + audio by stacking two -f lavfi -i inputs:

-f lavfi -i smptehdbars=size=1920x1080:rate=30 \
-f lavfi -i "sine=frequency=1000:sample_rate=48000"

ffmpeg auto-maps one video + one audio from those inputs — no -map usually needed for a single V+A pair.

Step 3 — Encode, duration, and container

Synthetic sources are infinite by default. Always bound the output with one of:

• duration=N inside the source expression, or
• -t N on the output (before the output filename).

Mixing both works but is easy to get wrong — prefer -t on the command line so the same flag caps both streams.

Recipe A — SMPTE HD bars + 1 kHz tone, 10 s, 1080p30, MP4

ffmpeg -f lavfi -i smptehdbars=size=1920x1080:rate=30 \
       -f lavfi -i "sine=frequency=1000:sample_rate=48000" \
       -t 10 \
       -c:v libx264 -pix_fmt yuv420p -crf 18 \
       -c:a aac -b:a 192k -ar 48000 \
       out.mp4

Recipe B — testsrc2 moving pattern + counter, 5 s, 720p30

ffmpeg -f lavfi -i testsrc2=size=1280x720:rate=30 -t 5 \
       -c:v libx264 -pix_fmt yuv420p -crf 20 out.mp4

Recipe C — Solid red fill, 5 s, 720p

ffmpeg -f lavfi -i "color=c=red:size=1280x720:rate=30:duration=5" \
       -c:v libx264 -pix_fmt yuv420p out.mp4

Recipe D — Animated red→blue gradient, 10 s 1080p

ffmpeg -f lavfi -i "gradients=s=1920x1080:duration=10:speed=0.01:c0=red:c1=blue" \
       -c:v libx264 -pix_fmt yuv420p out.mp4

Recipe E — Mandelbrot zoom, 10 s 1080p30

ffmpeg -f lavfi -i mandelbrot=size=1920x1080:rate=30 -t 10 \
       -c:v libx264 -pix_fmt yuv420p out.mp4

Recipe F — PAL 75 % bars, 10 s 576i

ffmpeg -f lavfi -i pal75bars=size=720x576:rate=25 -t 10 \
       -c:v libx264 -pix_fmt yuv420p out.mp4

Recipe G — Silent stereo track attached to a video-only source

ffmpeg -f lavfi -i testsrc2=size=1280x720:rate=30 \
       -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=48000 \
       -t 10 -c:v libx264 -pix_fmt yuv420p -c:a aac out.mp4

Recipe H — White / pink noise (audio only)

ffmpeg -f lavfi -i "anoisesrc=color=white:duration=5:sample_rate=48000:amplitude=0.3" \
       -c:a pcm_s16le noise.wav

Recipe I — Beep-style sine (0.25 s beep every 1 s)

ffmpeg -f lavfi -i "sine=frequency=440:beep_factor=4:duration=10:sample_rate=48000" \
       -c:a pcm_s16le beep.wav

Recipe J — Identity Hald CLUT (level 8 → 512×512 PNG)

ffmpeg -f lavfi -i haldclutsrc=level=8 -frames:v 1 hald.png

Recipe K — ColorChecker 24-patch PNG

ffmpeg -f lavfi -i colorchecker -frames:v 1 colorchecker.png
# Some builds accept size=:  -f lavfi -i colorchecker=patch_size=128x128:preset=reference

Recipe L — Broadcast line-up: SMPTE HD bars + 1 kHz tone at -20 dBFS

ffmpeg -f lavfi -i smptehdbars=size=1920x1080:rate=30 \
       -f lavfi -i "sine=frequency=1000:sample_rate=48000" \
       -af "volume=-20dB" \
       -t 60 -c:v libx264 -pix_fmt yuv420p -crf 16 \
       -c:a pcm_s24le lineup.mxf

Recipe M — Overlay a running timecode on SMPTE bars

Chain with drawtext (see ffmpeg-video-filter):

ffmpeg -f lavfi -i smptehdbars=size=1920x1080:rate=30 \
       -vf "drawtext=fontfile=/System/Library/Fonts/Menlo.ttc:text='%{pts\\:hms}':x=40:y=40:fontsize=64:fontcolor=white:box=1:boxcolor=black@0.6" \
       -t 10 -c:v libx264 -pix_fmt yuv420p bars_tc.mp4

Gotchas

• Every lavfi source uses -f lavfi -i <expression>. <expression> is filter-source syntax. It is NOT a filename; do not quote it as a path.
• Duration is not implicit. Without duration= on the source OR -t on the output, ffmpeg generates frames forever. Always bound one of them.
• Use -t or duration=, not both casually. They interact: -t caps the output, duration= caps the source. If they disagree the shorter one wins; prefer -t for consistency across V+A inputs.
• sine duration lives on the SOURCE. -f lavfi -i "sine=frequency=1000:duration=10" — the filter owns its own length. -t 10 also works and is clearer when you have two inputs.
• smptebars vs smptehdbars. smptebars = pre-HD 75 % bars at 320x240 default. smptehdbars = HD 100 % bars, aspect-correct. pal75bars / pal100bars are the PAL variants. Don't default to smptebars for HD deliverables.
• size= is often required. colorchecker, rgbtestsrc, yuvtestsrc, smptebars have small/fixed defaults in older ffmpeg builds. Pass size=WxH explicitly for HD.
• rate is VIDEO fps; sample_rate is AUDIO Hz. They're different knobs. Don't set rate=48000 on sine.
• Channel layout, not channel count. Most audio sources want channel_layout=stereo (or mono, 5.1). A raw channels=2 is accepted by some but not all — prefer the named layout.
• Combining V+A = two -f lavfi -i flags. Each input needs its own -f lavfi before its -i. One -f lavfi does not cover the next -i.
• Container must accept both streams. MP4 + libx264 + aac is the safe default. Don't write a video source into a .wav. Don't stuff pcm_s24le into plain MP4 (use MOV/MXF/MKV).
• Color names. c=red / c=0xff0000 / c=#ff0000 / c=random all work. Alpha via c=red@0.5.
• testsrc2 already burns in a frame counter and moving element — if you want it clean, use testsrc.
• haldclutsrc=level=N produces an N³ × N³ PNG (level 6 → 216×216, level 8 → 512×512, level 12 → 1728×1728). Level 8 is the common LUT-authoring default.
• anullsrc is identical regardless of duration. It's literal zeros. Use -t to cap length.
• Images need -frames:v 1. Otherwise ffmpeg keeps writing frames into out.png indefinitely (or errors on single-image muxers).
• Seek does not apply to generators. -ss 5 -f lavfi -i testsrc will NOT start the source at t=5. Generators start at zero; use -itsoffset or tpad if you need a cold start.
• Broadcast line-up level. SMPTE-compliant line-up = 1 kHz sine at -20 dBFS (EBU R68 = -18 dBFS). Apply with -af "volume=-20dB" — the sine source emits full-scale by default.
• flite TTS requires a custom build. ffmpeg -filters | grep flite — if empty, your build is stock; use external TTS and import the WAV.

Available scripts

• scripts/synth.py — argparse wrapper with subcommands for the common synthetic assets: bars, test-pattern, color, tone, noise, silence, hald-identity. Prints the exact ffmpeg command, supports --dry-run and --verbose. Stdlib only, non-interactive.

Workflow

1. Run the script for a standard recipe:

   uv run ${CLAUDE_SKILL_DIR}/scripts/synth.py bars --output out.mp4 --duration 10 --resolution 1920x1080 --fps 30 --tone-hz 1000 --hd
   uv run ${CLAUDE_SKILL_DIR}/scripts/synth.py test-pattern --output out.mp4 --kind testsrc2 --duration 5
   uv run ${CLAUDE_SKILL_DIR}/scripts/synth.py tone --output tone.wav --hz 1000 --duration 10
   uv run ${CLAUDE_SKILL_DIR}/scripts/synth.py noise --output noise.wav --color pink --duration 10
   uv run ${CLAUDE_SKILL_DIR}/scripts/synth.py hald-identity --output hald.png --level 8
   

2. For anything off the menu (custom gradient, aevalsrc expression, zoneplate, cellauto) build the -f lavfi -i chain by hand using Step 2.

Reference docs

• Read references/sources.md for full per-source option tables, color name list, aevalsrc grammar, and a recipe gallery (broadcast cal, ABX noise, 4K 60 fps stress, identity Hald, synthetic overlays).

Examples

Example 1: Broadcast cal leader, 1 minute, MXF

ffmpeg -f lavfi -i smptehdbars=size=1920x1080:rate=30 \
       -f lavfi -i "sine=frequency=1000:sample_rate=48000" \
       -af "volume=-20dB" \
       -t 60 -c:v libx264 -pix_fmt yuv420p -crf 16 -c:a pcm_s24le \
       leader.mxf

Example 2: 4 K 60 fps encoder stress-test, 30 s

ffmpeg -f lavfi -i testsrc2=size=3840x2160:rate=60 \
       -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=48000 \
       -t 30 -c:v libx264 -preset ultrafast -pix_fmt yuv420p stress.mp4

Example 3: Identity Hald CLUT round-trip

ffmpeg -f lavfi -i haldclutsrc=level=8 -frames:v 1 identity.png
# Grade identity.png in your DaVinci/Photoshop/LUT tool, save back as graded.png
# Apply the graded CLUT to any footage via ffmpeg-lut-grade:
#   ffmpeg -i source.mov -i graded.png -filter_complex "haldclut" out.mov

Example 4: Solid-color plate for lower-third compositing

ffmpeg -f lavfi -i "color=c=0x0a1f44:size=1920x200:rate=30:duration=10" \
       -c:v libx264 -pix_fmt yuv420p lower_third_bg.mp4

Troubleshooting

Error: No such filter: 'lavfi'

Cause: you passed -i lavfi:... instead of -f lavfi -i "...". Solution: -f lavfi is a format flag; it must precede -i, and the expression goes in -i.

Error: Option size not found

Cause: the specific source does not accept size= in your ffmpeg version (older builds of colorchecker, rgbtestsrc). Solution: pipe through a scale filter, e.g. -vf "scale=1920:1080", or upgrade ffmpeg.

Output file is empty / 0 bytes

Cause: no duration bound — ffmpeg was producing frames with no EOF signal and you killed it early. Solution: add -t N or duration=N inside the source expression.

sine audio is silent / file is tiny

Cause: forgot sample_rate=48000 and the default (44100) is being resampled to 0 by a bad -ar. Solution: set sample_rate= on the source AND -ar 48000 on the output if you want a specific rate.

Invalid duration specification for color

Cause: quoting ate the colons. color=c=red:size=1280x720:rate=30:duration=5 must be a single token to ffmpeg. Solution: wrap the whole expression in double quotes: -i "color=c=red:size=1280x720:rate=30:duration=5".

anoisesrc complains about color=pink

Cause: older ffmpeg builds only shipped white and pink; blue/brown/velvet came later. Solution: upgrade ffmpeg to 4.4+ for the full palette, or fall back to color=white and shape with -af "highpass=...".

Seeking into a synthetic source does nothing

Cause: -ss on a lavfi input is a no-op (no seekable timeline). Solution: offset via -itsoffset, or prepend blank frames with tpad=start_duration=….