video-assembly
Assemble final video from generated clips, audio, and assets using FFmpeg or Remotion. Handles concatenation, audio mixing, transitions, titles, and export. Use when combining multiple production outputs into a final deliverable.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/mckruz/comfyui-expert --skill video-assembly- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads video-assembly automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Video Assembly
Combines outputs from video and voice pipelines into final deliverable videos.
Two Assembly Modes
Mode 1: FFmpeg (Simple, Fast)
Best for: Concatenation, audio mixing, basic transitions, format conversion.
No dependencies beyond FFmpeg (pre-installed on most systems).
Mode 2: Remotion (Complex Compositions)
Best for: Animated captions, data visualizations, complex motion graphics, React-based templates.
Uses existing remotion-best-practices skill for guidance.
FFmpeg Operations
Concatenate Video Clips
# Create file list
echo "file 'clip1.mp4'" > filelist.txt
echo "file 'clip2.mp4'" >> filelist.txt
echo "file 'clip3.mp4'" >> filelist.txt
# Concatenate (same codec/resolution)
ffmpeg -f concat -safe 0 -i filelist.txt -c copy output.mp4
# Concatenate (different codecs/resolutions - re-encode)
ffmpeg -f concat -safe 0 -i filelist.txt -vf "scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2:(oh-ih)/2" -c:v libx264 -crf 19 output.mp4
Add Audio to Video
# Replace audio
ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 output.mp4
# Mix audio (keep original + add music)
ffmpeg -i video.mp4 -i music.mp3 -filter_complex "[0:a][1:a]amix=inputs=2:duration=first:dropout_transition=3" -c:v copy output.mp4
# Add audio with volume control
ffmpeg -i video.mp4 -i bgm.mp3 -filter_complex "[1:a]volume=0.3[bg];[0:a][bg]amix=inputs=2:duration=first" -c:v copy output.mp4
Add Subtitles
# Burn subtitles (SRT file)
ffmpeg -i video.mp4 -vf "subtitles=subs.srt:force_style='FontName=Arial,FontSize=24,PrimaryColour=&HFFFFFF,OutlineColour=&H000000,Outline=2'" -c:a copy output.mp4
# Burn subtitles (ASS file for styled)
ffmpeg -i video.mp4 -vf "ass=subs.ass" -c:a copy output.mp4
Transitions Between Clips
# Crossfade (2 second transition)
ffmpeg -i clip1.mp4 -i clip2.mp4 -filter_complex \
"[0:v]trim=0:5,setpts=PTS-STARTPTS[v0]; \
[1:v]trim=0:5,setpts=PTS-STARTPTS[v1]; \
[v0][v1]xfade=transition=fade:duration=2:offset=3[outv]" \
-map "[outv]" output.mp4
Extract/Manipulate Frames
# Extract frames
ffmpeg -i video.mp4 -vf "fps=1" frames/frame_%04d.png
# Create video from frames
ffmpeg -framerate 24 -i frames/frame_%04d.png -c:v libx264 -crf 19 -pix_fmt yuv420p output.mp4
# Speed up/slow down
ffmpeg -i video.mp4 -filter:v "setpts=0.5*PTS" -filter:a "atempo=2.0" fast.mp4 # 2x speed
ffmpeg -i video.mp4 -filter:v "setpts=2.0*PTS" -filter:a "atempo=0.5" slow.mp4 # 0.5x speed
Format Conversion
# MP4 (H.264) - universal compatibility
ffmpeg -i input.mov -c:v libx264 -crf 19 -preset medium -c:a aac -b:a 192k output.mp4
# WebM (VP9) - web delivery
ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 30 -b:v 0 -c:a libopus output.webm
# GIF (short clips)
ffmpeg -i input.mp4 -vf "fps=15,scale=480:-1:flags=lanczos" -loop 0 output.gif
Quality Presets
| Use Case | CRF | Resolution | Notes |
|---|---|---|---|
| Master/Archive | 15-17 | Original | Large files, best quality |
| YouTube Upload | 18-20 | 1920x1080 | Good balance |
| Social Media | 20-23 | 1080x1920 (vertical) | Smaller files |
| Preview/Draft | 25-28 | 1280x720 | Quick review |
Assembly Pipeline
Standard Video
1. Gather clips from comfyui-video-pipeline outputs
2. Gather audio from comfyui-voice-pipeline outputs
3. Normalize audio levels (-16 LUFS for YouTube)
4. Trim/arrange clips to match script timing
5. Add transitions between clips (if multiple)
6. Add background music (optional, lower volume)
7. Add subtitles (if applicable)
8. Export in target format
Talking Head Video
1. Lip-synced video from comfyui-voice-pipeline
2. Add intro/outro (if applicable)
3. Add lower thirds or name cards
4. Add background music at -20dB below speech
5. Normalize speech to -16 LUFS
6. Export
Tutorial/Walkthrough
1. Screen recordings + talking head overlay
2. Use Remotion for animated annotations
3. Add chapter markers
4. Add subtitles (auto-generate from audio)
5. Export with chapters embedded
Audio Normalization
# Normalize to -16 LUFS (YouTube standard)
ffmpeg -i input.mp4 -af "loudnorm=I=-16:TP=-1.5:LRA=11" -c:v copy output.mp4
# Two-pass normalization (more accurate)
ffmpeg -i input.mp4 -af loudnorm=I=-16:TP=-1.5:LRA=11:print_format=json -f null -
# Read measured values, then:
ffmpeg -i input.mp4 -af "loudnorm=I=-16:TP=-1.5:LRA=11:measured_I=-20:measured_TP=-2:measured_LRA=8:measured_thresh=-30" -c:v copy output.mp4
Remotion Integration
For complex compositions, delegate to remotion-best-practices skill.
Use Remotion when:
- Animated text/captions needed
- Data visualizations in video
- Complex motion graphics
- Programmatic/template-based video generation
- React-based UI elements as video overlays
Pass to Remotion:
- Clip paths and timings
- Text content and styles
- Animation specifications
- Output format requirements
Output Checklist
Before marking assembly as complete:
- Audio levels normalized (-16 LUFS for YouTube)
- No audio clipping (peak below -1.5 dB)
- Resolution matches delivery target
- Frame rate is consistent throughout
- No black frames at cuts
- Subtitles are timed correctly (if applicable)
- File size is reasonable for delivery platform
- Metadata is correct (title in filename)
Reference
references/workflows.md- Video output format settingsremotion-best-practicesskill - Complex composition guidance
FAQ
What does the video-assembly skill do?
Assemble final video from generated clips, audio, and assets using FFmpeg or Remotion. Handles concatenation, audio mixing, transitions, titles, and export. Use when combining multiple production outputs into a final deliverable.
How do I install video-assembly?
Run npx skills add https://github.com/mckruz/comfyui-expert --skill video-assembly in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/video-assembly/ (personal) or .claude/skills/video-assembly/ (project).
Which AI agents can use video-assembly?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is video-assembly safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains video-assembly?
It is published by mckruz in mckruz/comfyui-expert. It has 396 recorded installs.
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