promo-video-builder

Promo Video Builder Skill

Full pipeline: CI artifacts → video composition → voiceover → BGM → export.

Pipeline Overview

Phase 1: Asset Collection
  ├── GH API → download allure-report artifact → extract video.webm
  ├── Project screenshots (docs/images/*.png)
  └── Generate demo HTMLs from project config → record via Playwright
      ├── gen_arch_html.py -c arch-config.json → demo-architecture.html
      ├── gen_pipeline_html.py -c pipeline-config.json → demo-pipeline.html
      └── gen_logo_html.py -c logo-config.json → brand-logo.html

Phase 2: Audio Generation
  ├── edge-tts → per-chapter Chinese voiceover (zh-CN-YunyangNeural, rate=-12%)
  ├── Per-chapter pad/trim to match video chapter durations
  └── BGM: download from freepd.cn (NOT self-generated via Python sine waves)

Phase 3: Video Pre-processing
  ├── Normalize all clips to 1920×1080 30fps (critical for concat to work)
  ├── Re-encode 4K/10fps clips to 1080p 30fps
  ├── Still frames: replace tab-switching in long CI recordings
  └── Title cards: ffmpeg drawtext with Arial Unicode font

Phase 4: Audio Mixing (Python PCM, NOT ffmpeg amix)
  ├── Decode both voiceover + BGM to 48000Hz mono WAV
  ├── Sample-by-sample addition with fade envelope on BGM
  └── Encode to AAC → mux with video

Phase 5: FFmpeg Composition
  ├── Concat filter: assemble chapters (uniform codec required!)
  ├── Subtitles: burn SRT (chapter-aligned timing)
  └── Watermark: drawtext bottom-right

Other Skills to Call

Scripts

scripts/compose_video.py — Main Composition Engine

Orchestrates the entire pipeline. Edit main() to customize chapters, shot_map, and segments.

Key functions:

scripts/gen_voiceover.py — AI Voiceover

Generates per-chapter segments with edge-tts, then pads/trims each to exact chapter duration. Outputs voiceover_aligned.mp3 and per-chapter aligned_XX.mp3 files.

Usage: python3 gen_voiceover.py Edit SCRIPTS and CHAPTER_DURS to match your video chapter structure.

scripts/mix_audio.py — Python PCM Audio Mixing

CRITICAL: Do NOT use ffmpeg amix — it fails silently when input streams have different sample rates or channel counts (common with edge-tts 24000Hz mono + BGM 44100Hz stereo).

This script decodes both voiceover and BGM to 48000Hz mono WAV, mixes sample-by-sample with BGM volume envelope, and encodes to AAC.

Usage: python3 mix_audio.py vo_aligned.mp3 bgm.mp3 output.aac

scripts/gen_arch_html.py — Architecture Diagram Generator

Generates a star-topology architecture diagram as HTML. The center hub + surrounding service nodes with animated connection lines that light up sequentially.

# Use default Game Dev Studio config
python3 gen_arch_html.py -o demo-architecture.html

# Use custom project config
python3 gen_arch_html.py -c my-arch-config.json -o demo-architecture.html

Configurable via JSON:

• title, subtitle — diagram headings
• center — hub node (name, icon, details, color)
• services[] — list of service nodes (name, icon, label, color)
• animation_speed_ms — line lighting interval

See examples/arch-config.json for the full schema.

Supports 1–8 service nodes (pre-computed 8-point circle layout).

scripts/gen_pipeline_html.py — Pipeline/Flow Diagram Generator

Generates a horizontal pipeline flow diagram with animated stage highlighting.

python3 gen_pipeline_html.py -c my-pipeline-config.json -o demo-pipeline.html

Configurable:

• stages[] — process steps (name, icon)
• metrics[] — optional KPI cards
• show_preview — include before/after canvas previews
• animation_interval_ms — stage advance speed

scripts/gen_logo_html.py — Brand Logo Generator

Generates a brand logo animation page with shield, glow ring, sparkles, and gradient title.

python3 gen_logo_html.py --title "My Project" --subtitle "Powered by AI" -o brand-logo.html

Configurable:

• title, subtitle, subtitle_cn — text content
• theme_color, accent_color, secondary_color — brand colors

scripts/record_demos.cjs — Demo Recording

Records HTML/Canvas pages at 1920×1080 using Playwright + system Chrome. Outputs H.264 MP4.

Usage: node record_demos.cjs

Edit the DEMOS array to add auto-generated HTML pages:

Demo HTML Generation Workflow

Generate parameterized HTML animations for your project, then record them with Playwright:

# Step 1: Create config files for your project's services/pipeline

# Architecture diagram (star topology with your microservices)
python3 scripts/gen_arch_html.py -c examples/arch-config.json -o demo-architecture.html

# Pipeline flow (your build/deploy/processing pipeline)  
python3 scripts/gen_pipeline_html.py -c examples/pipeline-config.json -o demo-pipeline.html

# Brand logo (your project name and colors)
python3 scripts/gen_logo_html.py -c examples/logo-config.json -o brand-logo.html

# Step 2: Edit record_demos.cjs DEMOS array to include generated files

# Step 3: Record all HTML pages as MP4
node scripts/record_demos.cjs

The HTML generators accept JSON config so different projects can reuse them without code changes. Edit examples/*-config.json with your project's service names, pipeline nodes, and brand colors.

Critical Pitfalls

1. Codec Uniformity (MUST READ)

When using ffmpeg concat filter, ALL input files must have identical:

• Resolution (1920×1080)
• Frame rate (30fps)
• Pixel format (yuv420p)
• Codec (libx264)

Check before concat:

for f in chapter*.mp4; do
  ffprobe -v error -show_entries stream=width,height,r_frame_rate,pix_fmt -of csv=p=0 "$f"
done

If any differ, re-encode with normalize_video().

2. Chinese Font Rendering

ALWAYS use /Library/Fonts/Arial Unicode.ttf on macOS — NEVER PingFang.ttc.

3. Per-Chapter Audio-Video Sync (KEY FIX from v7)

Problem: Global silence padding (e.g., 1.5s) shifts ALL chapters, causing narration to overlap into adjacent chapters.

Solution: Pad/trim each voiceover segment to its chapter duration individually.

# For each chapter_i:
# if seg_dur > chapter_dur: atrim=0:chapter_dur
# if seg_dur < chapter_dur: apad=pad_dur=(chapter_dur - seg_dur)

Subtitles must use chapter video boundaries, NOT voiceover boundaries.

4. BGM Sourcing

Use freepd.cn (Chinese CDN mirror of FreePD.com, Kevin MacLeod's CC0 library):

• Access speed: ~230KB/s from China
• All tracks CC0: free commercial use, no attribution

Banned sources:

• Incompetech direct (too slow, ~5KB/s)
• Mixkit (hotlink protection returns 403)
• Bensound (requires browser interaction)
• Self-generated Python sine waves (user explicitly forbids)

Recommended tracks for tech product videos:

• Electronic/Chronos — sci-fi electronic, 129s
• Electronic/Space Ambience — ambient, 276s
• Upbeat/Motions — driving beat, 117s

Download pattern:

# 1. Fetch RSC payload to discover track hex paths
curl -s "https://freepd.cn/music?_rsc=1" > /tmp/freepd_rsc.txt

# 2. Extract hex-encoded track paths with Python
# 3. Download: curl -o track.mp3 "https://freepd.cn/api/music/{hex_path}"

5. GitHub Artifact Download

# GH_TOKEN must be set in environment (never hardcode in scripts)
# Find latest CI run
gh run list --repo OWNER/REPO --workflow=CI --limit=5

# List artifacts
gh api repos/OWNER/REPO/actions/runs/RUN_ID/artifacts

# Download allure-report
gh run download RUN_ID --repo OWNER/REPO --name allure-report --dir artifacts/

6. Tab Switching in CI Recordings

CI Playwright tests contain excessive tab-switching loops. Use extract_still_frame() to capture a single representative frame → static clip.

7. Playwright on Managed Python Runtime

Managed Python 3.13 may have greenlet code-signing issues. Use Node.js Playwright with system Chrome:

const { chromium } = require('playwright');
const browser = await chromium.launch({ channel: 'chrome' });

Video Structure Convention

Keep under 2 minutes. Typical 7-chapter structure:

1. AI visualization / intro (4-5s)
2. Logo + product name (5s)
3. Platform overview: team panel + studio (9-10s)
4. Smart features: CI clips + screenshots (10s)
5. Workflow: task board + autopilot (9s)
6. Microservices showcase (15s)
7. Artifacts + outro with GitHub URL (8-9s)

Total: ~62s