vhs-demo

Documents

Use when running demo recordings, diagnosing recording failures, or regenerating GIFs from existing MP4s. Covers the Docker + VHS + ffmpeg pipeline.

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VHS Demo Recording

Use this skill to run, debug, or regenerate gh-infra demo GIF recordings.

When To Use

Running make demo or docs/tapes/vhs.sh directly
Diagnosing why a recording failed or produced a 0-byte GIF
Regenerating GIFs from existing MP4s without re-recording
Understanding the recording pipeline

Prerequisites

Docker must be running
Go toolchain (for cross-compiling the Linux binary)

Pipeline

make demo
  1. go build -o docs/tapes/.gh-infra  (GOOS=linux GOARCH=amd64)
  2. docs/tapes/vhs.sh
     a. docker build → gh-infra-vhs image (VHS + vim)
     b. For each *.tape in parallel:
        docker run --memory=1g --cpus=2 → produces .mp4
     c. For each .mp4 sequentially:
        docker run jrottenberg/ffmpeg:7-alpine → produces .gif
  3. Copy GIFs to docs/public/
  4. Clean up .gh-infra binary

Why MP4 → GIF Instead of Direct GIF

VHS's built-in GIF output is unreliable when multiple containers run in parallel on macOS. The workaround is to output MP4 only from VHS, then convert to GIF via ffmpeg with high-quality settings (lanczos scaling, sierra2_4a dithering, 256 colors).

Key Files

File	Role
`docs/tapes/vhs.sh`	Orchestrator: parallel recording + sequential GIF conversion
`docs/tapes/Dockerfile`	`ghcr.io/charmbracelet/vhs` + vim
`docs/tapes/*.tape`	VHS scenario files
`docs/tapes/setup*.sh`	Per-demo setup scripts (mock data, gh wrapper)
`docs/tapes/mock-gh`	Generic mock for `gh` CLI
`docs/tapes/.gh-infra`	Cross-compiled Linux binary (ephemeral)

Output Locations

Raw recordings: docs/tapes/*.mp4 and docs/tapes/*.gif
Published assets: docs/public/demo*.gif (copied by Makefile)

Environment Variables

make demo forwards DEMO_ENV variables into Docker via -e flags. Use this to pass environment overrides (e.g. GH_INFRA_OUTPUT) into the recording containers.

Resource Planning

All tapes run in parallel. Each container requests --memory and --cpus (see vhs.sh). The total resource demand is:

total memory = number_of_tapes × per-container memory
total CPUs   = number_of_tapes × per-container CPUs

For example, 6 tapes × --memory=2g --cpus=2 = 12 GB / 12 CPUs.

This is constrained by Docker Desktop's resource allocation, not host RAM. Docker Desktop defaults are often low (e.g. 7.6 GB on a 24 GB machine). If total demand exceeds Docker Desktop's allocation, containers will OOM or produce 0-byte outputs.

When Adding New Tapes

Adding a tape increases parallel resource demand. Before adding, check:

Count existing tapes: ls docs/tapes/*.tape | wc -l
Calculate total: count × per-container memory
Compare against Docker Desktop memory allocation

If the total exceeds Docker Desktop's limit, you have two options:

Increase Docker Desktop memory — Open Docker Desktop → Settings → Resources → Memory. On an M-series Mac with 24+ GB RAM, allocating 16 GB is safe and is the recommended approach since it's a one-time setting.
Reduce per-container resources — Lower --memory in vhs.sh. This is a last resort since it may cause recording failures for complex tapes.

Recommended Docker Desktop Settings

For comfortable parallel recording of 6+ tapes:

Setting	Recommended
Memory	16 GB (minimum: number_of_tapes × 2 GB)
CPUs	8+

Troubleshooting

Symptom	Cause	Fix
0-byte GIF	MP4 was also 0-byte or missing	Check the tape's setup script and mock data
0-byte MP4	VHS crashed or setup script failed	Run the single tape manually: `docker run --rm -v docs/tapes:/data -w /data gh-infra-vhs <name>.tape`
`gh-infra: not found` in recording	Binary not copied or wrong arch	Verify `GOOS=linux GOARCH=amd64 go build` succeeded
Docker OOM	Container hit memory limit	Check Docker Desktop memory allocation (see Resource Planning above)
Multiple tapes fail simultaneously	Docker Desktop memory too low for parallel count	Increase Docker Desktop memory or reduce tape count
"Docker is not running"	Docker daemon not started	Start Docker Desktop or `dockerd`

Regenerating GIFs Only

To re-convert existing MP4s without re-recording, run the ffmpeg step manually:

docker run --rm -v docs/tapes:/data -w /data jrottenberg/ffmpeg:7-alpine \
  -y -i <name>.mp4 \
  -vf "fps=10,scale=1200:-1:flags=lanczos,split[s0][s1];[s0]palettegen=max_colors=256[p];[s1][p]paletteuse=dither=sierra2_4a" \
  <name>.gif