Asciinema Player

asciinema-player

Play terminal session recordings (.cast files) in a dedicated iTerm2 window with full playback controls. Opens a clean window (bypasses default arrangements) for distraction-free viewing.

Platform: macOS only (requires iTerm2)

Self-Evolving Skill: This skill improves through use. If instructions are wrong, parameters drifted, or a workaround was needed — fix this file immediately, don't defer. Only update for real, reproducible issues.

When to Use This Skill

Use this skill when:

• Playing back .cast recordings in iTerm2
• Reviewing session recordings without browser limitations
• Handling large recordings (>100MB) that crash browser players
• Demoing or reviewing terminal sessions

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Why iTerm2 Instead of Browser?

Decision: iTerm2 CLI is the only reliable method for large recordings.

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Requirements

Note: This skill is macOS-only. Linux users should run asciinema play directly in their terminal.

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Workflow Phases (ALL MANDATORY)

IMPORTANT: All phases are MANDATORY. Do NOT skip any phase. AskUserQuestion MUST be used at each decision point.

Phase 0: Preflight Checks

Purpose: Verify iTerm2 and asciinema are installed.

Step 0.1: Check Dependencies

# Check iTerm2 is installed
ls -d /Applications/iTerm.app 2>/dev/null && echo "iTerm2: OK" || echo "iTerm2: MISSING"

# Check asciinema CLI
which asciinema && asciinema --version

Step 0.2: Report Status and Ask for Installation

MANDATORY AskUserQuestion if any dependency is missing:

Question: "Required dependencies are missing. Install them?"
Header: "Setup"
Options:
  - Label: "Install all (Recommended)"
    Description: "Will install: {list of missing: iTerm2, asciinema}"
  - Label: "Cancel"
    Description: "Abort - cannot proceed without dependencies"

Step 0.3: Install Missing Dependencies (if confirmed)

# Install iTerm2
brew install --cask iterm2

# Install asciinema CLI
brew install asciinema

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Phase 1: File Selection (MANDATORY)

Purpose: Discover and select the recording to play.

Step 1.1: Discover Recordings

# Search for .cast files in common locations
fd -e cast . --max-depth 5 2>/dev/null | head -20

# Also check common locations
ls -lh ~/scripts/tmp/*.cast 2>/dev/null
ls -lh ~/.local/share/asciinema/*.cast 2>/dev/null
ls -lh ./tmp/*.cast 2>/dev/null

Step 1.2: Get File Info

# Get file size and line count for selected file
ls -lh {file_path}
wc -l {file_path}

Step 1.3: Present File Selection (MANDATORY AskUserQuestion)

If user provided path directly, confirm:

Question: "Play this recording?"
Header: "Confirm"
Options:
  - Label: "Yes, play {filename}"
    Description: "{size}, {line_count} events"
  - Label: "Choose different file"
    Description: "Browse for other recordings"

If no path provided, discover and present options:

Question: "Which recording would you like to play?"
Header: "Recording"
Options:
  - Label: "{filename} ({size})"
    Description: "{line_count} events"
  - ... (up to 4 most recent)

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Phase 2: Playback Settings (MANDATORY)

Purpose: Configure playback options before launching iTerm2.

Step 2.1: Ask Playback Speed (MANDATORY AskUserQuestion)

Question: "Select playback speed:"
Header: "Speed"
Options:
  - Label: "2x (fast)"
    Description: "Good for review, see everything"
  - Label: "6x (very fast)"
    Description: "Quick scan of long sessions"
  - Label: "16x (ultra fast)"
    Description: "Rapid skim for 700MB+ files"
  - Label: "Custom"
    Description: "Enter your own speed multiplier"

If "Custom" selected, ask for speed value (use Other option for numeric input).

Step 2.2: Ask Additional Options (MANDATORY AskUserQuestion)

Question: "Select additional playback options:"
Header: "Options"
multiSelect: true
Options:
  - Label: "Limit idle time (2s)"
    Description: "Cap pauses to 2 seconds max (recommended)"
  - Label: "Loop playback"
    Description: "Restart automatically when finished"
  - Label: "Resize terminal"
    Description: "Match terminal size to recording dimensions"
  - Label: "Pause on markers"
    Description: "Auto-pause at marked points (for demos)"

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Phase 3: Launch in iTerm2

Purpose: Open clean iTerm2 window and start playback.

Step 3.1: Build Command

Construct the asciinema play command based on user selections:

# Example with all options
asciinema play -s 6 -i 2 -l -r /path/to/recording.cast

Option flags:

• -s {speed} - Playback speed
• -i 2 - Idle time limit (if selected)
• -l - Loop (if selected)
• -r - Resize terminal (if selected)
• -m - Pause on markers (if selected)

Step 3.2: Launch iTerm2 Window

Use AppleScript to open a clean window (bypasses default arrangements):

osascript -e 'tell application "iTerm2"
    create window with default profile
    tell current window
        tell current session
            write text "asciinema play -s {speed} {options} {file_path}"
        end tell
    end tell
end tell'

Step 3.3: Display Controls Reference

## Playback Started

**Recording:** `{filename}`
**Speed:** {speed}x
**Options:** {options_summary}

### Keyboard Controls

| Key      | Action                            |
| -------- | --------------------------------- |
| `Space`  | Pause / Resume                    |
| `Ctrl+C` | Stop playback                     |
| `.`      | Step forward (when paused)        |
| `]`      | Skip to next marker (when paused) |

### Tips

- Press `Space` to pause anytime
- Use `.` to step through frame by frame
- `Ctrl+C` to exit when done

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TodoWrite Task Template (MANDATORY)

Load this template into TodoWrite before starting:

1. [Preflight] Check iTerm2 installed
2. [Preflight] Check asciinema CLI installed
3. [Preflight] AskUserQuestion: install missing deps (if needed)
4. [Preflight] Install dependencies (if confirmed)
5. [Selection] Get file info (size, events)
6. [Selection] AskUserQuestion: confirm file selection
7. [Settings] AskUserQuestion: playback speed
8. [Settings] AskUserQuestion: additional options (multi-select)
9. [Launch] Build asciinema play command
10. [Launch] Execute AppleScript to open iTerm2
11. [Launch] Display controls reference

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CLI Options Reference

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AppleScript Reference

Open Clean iTerm2 Window (No Default Arrangement)

tell application "iTerm2"
    create window with default profile
    tell current window
        tell current session
            write text "your command here"
        end tell
    end tell
end tell

Why this works: create window with default profile creates a fresh window, bypassing any saved window arrangements.

One-liner for Bash

osascript -e 'tell application "iTerm2"
    create window with default profile
    tell current window
        tell current session
            write text "asciinema play -s 6 -i 2 /path/to/file.cast"
        end tell
    end tell
end tell'

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Troubleshooting

"Device not configured" error

Cause: Running asciinema play from a non-TTY context (e.g., Claude Code's Bash tool)

Fix: Use AppleScript to open a real iTerm2 window (this skill does this automatically)

Recording plays too fast/slow

Fix: Use the speed AskUserQuestion to select appropriate speed:

• 2x for careful review
• 6x for quick scan
• 16x for ultra-fast skim of very long recordings

iTerm2 not opening

Cause: iTerm2 not installed or AppleScript permissions not granted

Fix:

1. Install iTerm2: brew install --cask iterm2 2. Grant permissions: System Settings → Privacy & Security → Automation → Allow Terminal/Claude to control iTerm2

Large file (>500MB) considerations

The CLI player streams from disk, so file size doesn't cause memory issues. However:

• Very long recordings may benefit from higher speeds (6x, 16x)
• Use -i 2 to skip idle time
• Consider splitting very long recordings

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Post-Change Checklist

After modifying this skill:

1. [ ] Preflight checks verify iTerm2 and asciinema 2. [ ] AskUserQuestion phases use proper multiSelect where applicable 3. [ ] AppleScript uses heredoc wrapper for bash compatibility 4. [ ] Speed options match CLI capability (-s flag) 5. [ ] TodoWrite template matches actual workflow phases

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Reference Documentation

• asciinema play Usage
• asciinema CLI Options
• iTerm2 AppleScript Documentation
• asciinema Markers

Post-Execution Reflection

After this skill completes, reflect before closing the task:

0. Locate yourself. — Find this SKILL.md's canonical path before editing. 1. What failed? — Fix the instruction that caused it. 2. What worked better than expected? — Promote to recommended practice. 3. What drifted? — Fix any script, reference, or dependency that no longer matches reality. 4. Log it. — Evolution-log entry with trigger, fix, and evidence.

Do NOT defer. The next invocation inherits whatever you leave behind.

Evolution Log

Convention: Reverse chronological order (newest on top, oldest at bottom). Prepend new entries.

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2026-02-26: Initial Evolution Log

Status: Skill is in use and maintained. Track improvements here.

Purpose

This evolution log tracks updates to the asciinema-player skill. Each entry should note:

• What changed (content, structure, tooling)
• Why it changed (bug fix, feature request, best practice)
• Files affected

How to Use

1. When updating SKILL.md or references, add an entry here with the date 2. Keep entries reverse-chronological (newest first) 3. Link to ADRs or GitHub issues when relevant 4. Reference specific line changes when helpful

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