Reference: Core CLI Command and Schema Specification

This document provides a technical reference for the multimux-core CLI commands, JSON option schemas, and piped IPC communication events.

CLI Syntax

The compiled native core binary supports two commands:

multimux-core probe <file_path>
multimux-core mux [<options_json_string>]

1. Probe Command

  • Arguments: <file_path> (Absolute path to the media file).

  • Behavior: Runs ffprobe as a piped process, filters metadata, and returns a JSON payload detailing the container format and available streams.

2. Mux Command

  • Arguments: [<options_json_string>] (Optional JSON string. If omitted, the binary reads from the standard input stream).

  • Behavior: Orchestrates the multi-track audio mixdown using ffmpeg, adjusts process priorities, and writes progress lines to stdout.

JSON Schemas

Stdin: Mux Configuration Schema

When invoking the mux command, Electron passes this options payload to the standard input of the D-lang supervisor:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "properties": {
    "filePath": { "type": "string" },
    "outputPath": { "type": "string" },
    "audioCodec": { "type": "string", "enum": ["aac", "libopus", "copy"] },
    "audioBitrate": { "type": "string", "pattern": "^[0-9]+k$" },
    "duration": { "type": "number", "minimum": 0.0 },
    "selectedStreams": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "relativeIndex": { "type": "integer", "minimum": 0 },
          "volume": { "type": "number", "minimum": 0.0, "maximum": 2.0 }
        },
        "required": ["relativeIndex", "volume"]
      }
    }
  },
  "required": ["filePath", "outputPath", "audioCodec", "audioBitrate", "duration", "selectedStreams"]
}

Stdout: IPC Event Streams

During execution, multimux-core emits single-line JSON structures to stdout separated by standard newlines (\n or \r\n).

1. Log Event

Sent whenever FFmpeg outputs debugging logs or progress metrics to stderr:

{ "type": "log", "message": "Spawning FFmpeg supervisor..." }

2. Progress Event

Sent dynamically as timestamps are extracted from standard error:

{ "type": "progress", "percent": 45.20 }

3. Error Event

Sent if the command fails or parses invalid option schemas:

{ "type": "error", "message": "ffmpeg failed with exit code 1." }

4. Completion Event

Sent when the subprocess completes with exit code 0:

{ "type": "done" }