asciinema-cast-format

# asciinema-cast-format Reference documentation for the asciinema v3 .cast file format (asciicast v2 specification). > **Platform**: All platforms (documentation only) > **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: - Parsing or inspecting .cast file structure - Understanding NDJSON header and event formats - Building tools that read or write .cast files - Debugging recording issues or format errors - Learning the asciicast v2 specification --- ## Format Overview Asciinema v3 uses NDJSON (Newline Delimited JSON) format: - Line 1: Header object with recording metadata - Lines 2+: Event arrays with timestamp, type, and data --- ## Header Specification The first line is a JSON object with these fields: | Field | Type | Required | Description | | ----------- | ------ | -------- | ------------------------------------------- | | `version` | int | Yes | Format version (always 2 for v3 recordings) | | `width` | int | Yes | Terminal width in columns | | `height` | int | Yes | Terminal height in rows | | `timestamp` | int | No | Unix timestamp of recording start | | `duration` | float | No | Total duration in seconds ...