asciinema-converter

asciinema-converter

Convert asciinema .cast recordings to clean .txt files for Claude Code analysis. Achieves 950:1 compression (3.8GB -> 4MB) by stripping ANSI codes and JSON structure.

Platform: macOS, Linux (requires asciinema CLI v2.4+)

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:

• Converting .cast recordings to searchable .txt format
• Preparing recordings for Claude Code Read/Grep tools
• Batch converting multiple recordings
• Reducing storage size of session archives
• Extracting clean text from ANSI-coded terminal output

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Why Convert?

Format	Size (22h session)	Claude Code Compatible	Searchable
.cast	3.8GB	No (NDJSON + ANSI)	Via jq
.txt	~4MB	Yes (clean text)	Grep/Read

Key benefit: Claude Code's Read and Grep tools work directly on .txt output.

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Requirements

Component	Required	Installation	Notes
asciinema	Yes	brew install asciinema	v2.4+ for convert cmd

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Workflow Overview

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

Single File Mode (Phases 0-6)

Phase	Purpose	Key Action
0	Preflight check	Verify asciinema CLI v2.4+
1	File discovery & selection	AskUserQuestion: file to convert
2	Output options	AskUserQuestion: conversion opts
3	Output location	AskUserQuestion: save destination
4	Execute conversion	asciinema convert -f txt
5	Timestamp index	Optional [HH:MM:SS] index
6	Next steps	AskUserQuestion: what's next

Full implementation details: Workflow Phases

Batch Mode (Phases 7-10)

Activated via --batch flag. Converts all .cast files in a directory with organized output.

Phase	Purpose	Key Action
7	Source selection	AskUserQuestion (skip if --source)
8	Output organization	AskUserQuestion (skip if --output-dir)
9	Execute batch	Convert all with progress reporting
10	Batch next steps	AskUserQuestion: what's next

Full implementation details: Batch Workflow

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iTerm2 Filename Format

iTerm2 auto-logged files follow this format:

{creationTimeString}.{profileName}.{termid}.{iterm2.pid}.{autoLogId}.cast

Example: 20260118_232025.Claude Code.w0t1p1.70C05103-2F29-4B42-8067-BE475DB6126A.68721.4013739999.cast

Component	Description	Example
creationTimeString	YYYYMMDD_HHMMSS	20260118_232025
profileName	iTerm2 profile (may have dots)	Claude Code
termid	Window/tab/pane identifier	w0t1p1
iterm2.pid	iTerm2 process UUID	70C05103-2F29-4B42-8067-BE475DB6126A
autoLogId	Session auto-log identifier	68721.4013739999

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CLI Quick Reference

# Basic conversion
asciinema convert -f txt recording.cast recording.txt

# Check asciinema version
asciinema --version

# Verify convert command exists
asciinema convert --help

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Reference Documentation

Internal References

• Workflow Phases - Single file mode phases 0-6 with full scripts
• Batch Workflow - Batch mode phases 7-10 with full scripts
• Task Templates - TodoWrite templates for single and batch modes
• Post-Change Checklist - Verification after modifications
• Anti-Patterns - Common mistakes to avoid
• Batch Processing - Patterns for bulk conversion
• Integration Guide - Chaining with analyze/summarize

External References

• asciinema convert command
• asciinema-cast-format skill

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Troubleshooting

Issue	Cause	Solution
convert command not found	asciinema too old	Upgrade: brew upgrade asciinema (need v2.4+)
asciinema not installed	Missing CLI	brew install asciinema
Empty output file	Corrupted .cast input	Verify .cast file has valid NDJSON structure
Conversion failed	Invalid cast format	Check header line is valid JSON with jq
numfmt not found	macOS missing coreutils	Use raw byte count or brew install coreutils
stat syntax error	Linux vs macOS difference	Script handles both; check stat version
Batch skipping all files	All .txt already exist	Use --skip-existing=false to reconvert
Permission denied on output	Directory not writable	Check output directory permissions

Post-Execution Reflection

After this skill completes, check before closing:

1. Did the command succeed? — If not, fix the instruction or error table that caused the failure.
2. Did parameters or output change? — If the underlying tool's interface drifted, update Usage examples and Parameters table to match.
3. Was a workaround needed? — If you had to improvise (different flags, extra steps), update this SKILL.md so the next invocation doesn't need the same workaround.

Only update if the issue is real and reproducible — not speculative.