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+)
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.
Requirements Component Required Installation Notes asciinema Yes brew install asciinema v2.4+ for convert cmd 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 Check
Purpose: Verify asciinema is installed and supports convert command.
/usr/bin/env bash << 'PREFLIGHT_EOF' if command -v asciinema &>/dev/null; then VERSION=$(asciinema --version | head -1) echo "asciinema: $VERSION"
# Check if convert command exists (v2.4+) if asciinema convert --help &>/dev/null 2>&1; then echo "convert: available" else echo "convert: MISSING (update asciinema to v2.4+)" fi else echo "asciinema: MISSING" fi PREFLIGHT_EOF
If asciinema is NOT installed or convert is missing, use AskUserQuestion:
Question: "asciinema CLI issue detected. How would you like to proceed?" Header: "Setup" Options: - Label: "Install/upgrade asciinema (Recommended)" Description: "Run: brew install asciinema (or upgrade if outdated)" - Label: "Show manual instructions" Description: "Display installation commands for all platforms" - Label: "Cancel" Description: "Exit without converting"
Phase 1: File Discovery & Selection (MANDATORY)
Purpose: Discover .cast files and let user select which to convert.
Step 1.1: Discover .cast Files /usr/bin/env bash << 'DISCOVER_EOF'
Search for .cast files with metadata
for file in $(fd -e cast . --max-depth 5 2>/dev/null | head -10); do SIZE=$(ls -lh "$file" 2>/dev/null | awk '{print $5}') LINES=$(wc -l < "$file" 2>/dev/null | tr -d ' ') DURATION=$(head -1 "$file" 2>/dev/null | jq -r '.duration // "unknown"' 2>/dev/null) BASENAME=$(basename "$file") echo "FILE:$file|SIZE:$SIZE|LINES:$LINES|DURATION:$DURATION|NAME:$BASENAME" done DISCOVER_EOF
Step 1.2: Present File Selection (MANDATORY AskUserQuestion)
Use discovery results to populate options:
Question: "Which recording would you like to convert?" Header: "Recording" Options: - Label: "{filename} ({size})" Description: "{line_count} events, {duration}s duration" - Label: "{filename2} ({size2})" Description: "{line_count2} events, {duration2}s duration" - Label: "Browse for file" Description: "Search in a different directory" - Label: "Enter path" Description: "Provide a custom path to a .cast file"
Phase 2: Output Options (MANDATORY)
Purpose: Let user configure conversion behavior.
Question: "Select conversion options:" Header: "Options" multiSelect: true Options: - Label: "Plain text output (Recommended)" Description: "Convert to .txt with all ANSI codes stripped" - Label: "Create timestamp index" Description: "Generate [HH:MM:SS] indexed version for navigation" - Label: "Split by idle time" Description: "Create separate chunks at 30s+ pauses" - Label: "Preserve terminal dimensions" Description: "Add header with original terminal size"
Phase 3: Output Location (MANDATORY)
Purpose: Let user choose where to save the output.
Question: "Where should the output be saved?" Header: "Output" Options: - Label: "Same directory as source (Recommended)" Description: "Save {filename}.txt next to {filename}.cast" - Label: "Workspace tmp/" Description: "Save to ${PWD}/tmp/" - Label: "Custom path" Description: "Specify a custom output location"
Phase 4: Execute Conversion
Purpose: Run the conversion and report results.
Step 4.1: Run asciinema convert /usr/bin/env bash << 'CONVERT_EOF' INPUT_FILE="${1:?Input file required}" OUTPUT_FILE="${2:?Output file required}"
echo "Converting: $INPUT_FILE" echo "Output: $OUTPUT_FILE" echo ""
Run conversion
asciinema convert -f txt "$INPUT_FILE" "$OUTPUT_FILE"
if [[ $? -eq 0 && -f "$OUTPUT_FILE" ]]; then echo "Conversion successful" else echo "ERROR: Conversion failed" exit 1 fi CONVERT_EOF
Step 4.2: Report Compression /usr/bin/env bash << 'REPORT_EOF' INPUT_FILE="${1:?}" OUTPUT_FILE="${2:?}"
Get file sizes (macOS compatible)
INPUT_SIZE=$(stat -f%z "$INPUT_FILE" 2>/dev/null || stat -c%s "$INPUT_FILE" 2>/dev/null) OUTPUT_SIZE=$(stat -f%z "$OUTPUT_FILE" 2>/dev/null || stat -c%s "$OUTPUT_FILE" 2>/dev/null)
Calculate ratio
if [[ $OUTPUT_SIZE -gt 0 ]]; then RATIO=$((INPUT_SIZE / OUTPUT_SIZE)) else RATIO=0 fi
Human-readable sizes
INPUT_HR=$(numfmt --to=iec "$INPUT_SIZE" 2>/dev/null || echo "$INPUT_SIZE bytes") OUTPUT_HR=$(numfmt --to=iec "$OUTPUT_SIZE" 2>/dev/null || echo "$OUTPUT_SIZE bytes")
echo "" echo "=== Conversion Complete ===" echo "Input: $INPUT_HR" echo "Output: $OUTPUT_HR" echo "Compression: ${RATIO}:1" echo "Output path: $OUTPUT_FILE" REPORT_EOF
Phase 5: Create Timestamp Index (if selected)
Purpose: Generate indexed version for navigation.
/usr/bin/env bash << 'INDEX_EOF' INPUT_CAST="${1:?}" OUTPUT_INDEX="${2:?}"
echo "Creating timestamp index..."
Process .cast file to indexed format
( echo "# Recording Index" echo "# Format: [HH:MM:SS] content" echo "#"
cumtime=0 tail -n +2 "$INPUT_CAST" | while IFS= read -r line; do # Extract timestamp and content ts=$(echo "$line" | jq -r '.[0]' 2>/dev/null) type=$(echo "$line" | jq -r '.[1]' 2>/dev/null) content=$(echo "$line" | jq -r '.[2]' 2>/dev/null)
if [[ "$type" == "o" && -n "$content" ]]; then
# Format timestamp as HH:MM:SS
hours=$((${ts%.*} / 3600))
mins=$(((${ts%.*} % 3600) / 60))
secs=$((${ts%.*} % 60))
timestamp=$(printf "%02d:%02d:%02d" "$hours" "$mins" "$secs")
# Clean and output (strip ANSI, limit length)
clean=$(echo "$content" | sed 's/\x1b\[[0-9;]*[a-zA-Z]//g' | tr -d '\r' | head -c 200)
[[ -n "$clean" ]] && echo "[$timestamp] $clean"
fi
done ) > "$OUTPUT_INDEX"
echo "Index created: $OUTPUT_INDEX" wc -l "$OUTPUT_INDEX" INDEX_EOF
Phase 6: Next Steps (MANDATORY)
Purpose: Guide user to next action.
Question: "Conversion complete. What's next?" Header: "Next" Options: - Label: "Analyze with /asciinema-tools:analyze" Description: "Run keyword extraction on the converted file" - Label: "Open in editor" Description: "View the converted text file" - Label: "Done" Description: "Exit - no further action needed"
Batch Mode (Phases 7-9)
Batch mode converts all .cast files in a directory with organized output. Activated via --batch flag.
Use case: Convert 1000+ iTerm2 auto-logged recordings efficiently.
Phase 7: Batch Source Selection
Purpose: Select source directory for batch conversion.
Trigger: --batch flag without --source argument.
Question: "Select source directory for batch conversion:" Header: "Source" Options: - Label: "~/asciinemalogs (iTerm2 default)" (Recommended) Description: "Auto-logged iTerm2 recordings" - Label: "~/Downloads" Description: "Recent downloads containing .cast files" - Label: "Current directory" Description: "Convert .cast files in current working directory" - Label: "Custom path" Description: "Specify a custom source directory"
Skip condition: If --source argument provided, skip this phase.
Phase 8: Batch Output Organization
Purpose: Configure output directory structure.
Trigger: --batch flag without --output-dir argument.
Question: "Where should converted files be saved?" Header: "Output" Options: - Label: "~/Downloads/cast-txt/ (Recommended)" Description: "Organized output directory, easy to find" - Label: "Same as source" Description: "Save .txt files next to .cast files" - Label: "Custom directory" Description: "Specify a custom output location"
Skip condition: If --output-dir argument provided, skip this phase.
Phase 9: Execute Batch Conversion
Purpose: Convert all files with progress reporting.
/usr/bin/env bash << 'BATCH_EOF' SOURCE_DIR="${1:?Source directory required}" OUTPUT_DIR="${2:?Output directory required}" SKIP_EXISTING="${3:-true}"
mkdir -p "$OUTPUT_DIR"
echo "=== Batch Conversion ===" echo "Source: $SOURCE_DIR" echo "Output: $OUTPUT_DIR" echo "Skip existing: $SKIP_EXISTING" echo ""
total=0 converted=0 skipped=0 failed=0 total_input_size=0 total_output_size=0
Count files first
total=$(find "$SOURCE_DIR" -maxdepth 1 -name "*.cast" -type f 2>/dev/null | wc -l | tr -d ' ') echo "Found $total .cast files" echo ""
for cast_file in "$SOURCE_DIR"/*.cast; do [[ -f "$cast_file" ]] || continue
basename=$(basename "$cast_file" .cast) txt_file="$OUTPUT_DIR/${basename}.txt"
# Skip if already converted (and skip mode enabled) if [[ "$SKIP_EXISTING" == "true" && -f "$txt_file" ]]; then echo "SKIP: $basename (already exists)" ((skipped++)) continue fi
# Get input size input_size=$(stat -f%z "$cast_file" 2>/dev/null || stat -c%s "$cast_file" 2>/dev/null)
# Convert if asciinema convert -f txt "$cast_file" "$txt_file" 2>/dev/null; then output_size=$(stat -f%z "$txt_file" 2>/dev/null || stat -c%s "$txt_file" 2>/dev/null) if [[ $output_size -gt 0 ]]; then ratio=$((input_size / output_size)) else ratio=0 fi echo "OK: $basename (${ratio}:1 compression)" ((converted++)) total_input_size=$((total_input_size + input_size)) total_output_size=$((total_output_size + output_size)) else echo "FAIL: $basename" ((failed++)) fi done
echo "" echo "=== Batch Complete ===" echo "Converted: $converted" echo "Skipped: $skipped" echo "Failed: $failed"
if [[ $total_output_size -gt 0 ]]; then overall_ratio=$((total_input_size / total_output_size)) echo "Overall compression: ${overall_ratio}:1" fi echo "Output directory: $OUTPUT_DIR" BATCH_EOF
Phase 10: Batch Next Steps
Purpose: Guide user after batch conversion.
Question: "Batch conversion complete. What's next?" Header: "Next" Options: - Label: "Batch analyze with /asciinema-tools:analyze --batch" Description: "Run keyword extraction on all converted files" - Label: "Open output directory" Description: "View converted files in Finder" - Label: "Done" Description: "Exit - no further action needed"
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 TodoWrite Task Template Single File Mode 1. [Preflight] Check asciinema CLI and convert command 2. [Preflight] Offer installation if missing 3. [Discovery] Find .cast files with metadata 4. [Selection] AskUserQuestion: file to convert 5. [Options] AskUserQuestion: conversion options (multi-select) 6. [Location] AskUserQuestion: output location 7. [Convert] Run asciinema convert -f txt 8. [Report] Display compression ratio and output path 9. [Index] Create timestamp index if requested 10. [Next] AskUserQuestion: next steps
Batch Mode (--batch flag) 1. [Preflight] Check asciinema CLI and convert command 2. [Preflight] Offer installation if missing 3. [Source] AskUserQuestion: source directory (skip if --source) 4. [Output] AskUserQuestion: output directory (skip if --output-dir) 5. [Batch] Execute batch conversion with progress 6. [Report] Display aggregate compression stats 7. [Next] AskUserQuestion: batch next steps
Post-Change Checklist
After modifying this skill:
Single File Mode Preflight check detects asciinema version correctly Discovery uses heredoc wrapper for bash compatibility Compression calculation handles macOS stat syntax All AskUserQuestion phases are present TodoWrite template matches actual workflow Batch Mode --batch flag triggers batch workflow (phases 7-10) --source skips Phase 7 (source selection) --output-dir skips Phase 8 (output organization) --skip-existing prevents re-conversion of existing files Aggregate compression ratio calculated correctly iTerm2 filename format documented 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
Reference Documentation Internal References 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