MIDI Type 1 -> Type 0 Converter (WordPress Plugin)

Frontend WordPress plugin that lets users upload .mid/.midi files, converts MIDI Type 1 to Type 0 asynchronously, and provides per-file or batch ZIP downloads.

Features

• Frontend upload UI via shortcode: [midi_type0_converter]
• Multi-file upload with per-job status polling
• Asynchronous conversion pipeline (queued -> processing -> done/error)
• Optional routing of all channel events to MIDI Channel 1
• Optional removal of General MIDI percussion on Channel 10 while routing parts to Channel 1
• Optional removal of descriptive metadata while preserving the first title
• Per-file signed download links
• Batch ZIP download link (when ZipArchive is available)
• Private storage under wp-content/uploads/mtc-private
• Rate limits for upload/status/download endpoints
• Optional ClamAV scan before storing uploads (disabled by default)

Requirements

• WordPress (plugin architecture + AJAX + cron APIs)
• PHP 8.0+ recommended (uses modern PHP features like match)
• ZipArchive extension for "Download All (ZIP)"
• Optional: clamdscan for antivirus scanning when enabled by filter

Installation

1. Copy this project folder into wp-content/plugins/.
2. Activate the plugin in WordPress admin.
3. Add shortcode [midi_type0_converter] to a page/post.
4. Open that page and upload MIDI files.

Usage

1. Select one or more .mid/.midi files.
2. Choose any settings under Options:
   • Play all parts on the piano (MIDI Channel 1) routes every part to the piano itself instead of playing some parts through a Disklavier's speakers.
     • Exclude percussion (MIDI Channel 10) becomes available with that option and prevents General MIDI drum events from playing as piano notes.
   • Strip extra metadata can help files that will not load, start, or play correctly on some Disklaviers and older MIDI players. It removes unnecessary descriptive text while keeping the first title and playback data.
3. Click Upload & Convert.
4. Polling starts automatically and status updates appear in the table.
5. Download files individually as they complete, or use Download All (ZIP) when available.

How It Works

• Upload endpoint: mtc_upload (wp_ajax_*)
  • Validates nonce, extension, MIDI header (MThd), size limits, and optional ClamAV scan when enabled.
  • Persists job row in DB table with initial queued status.
  • Schedules background job via wp_schedule_single_event.
• Status endpoint: mtc_status (wp_ajax_*)
  • Returns jobs for a batch_id, statuses, and signed download URLs.
  • Nudges stale queued jobs (cron spawn + fallback inline processing for very stale items).
• Conversion worker: mtc_process_job
  • Claims queued jobs atomically and runs pure-PHP conversion (includes/class-mtc-midi-converter.php).
• Download handlers:
  • ?mtc_download=1... for a single converted MIDI
  • ?mtc_zip=1... for batch ZIP
  • Links are HMAC-signed and time-limited.

Data Model

Table: {wp_prefix}mtc_jobs

• id
• batch_id
• original_name
• original_path
• converted_path
• status (queued, processing, done, error)
• error_msg
• force_channel_zero (0 or 1; routes to user-facing MIDI Channel 1)
• exclude_percussion (0 or 1; only effective with force_channel_zero)
• strip_extra_metadata (0 or 1)
• created_at
• updated_at

Configuration (Filters)

Add filters in a must-use plugin or theme functions.php.

add_filter('mtc_max_upload_bytes', fn() => 10 * 1024 * 1024);
add_filter('mtc_max_files_per_batch', fn() => 200);
add_filter('mtc_download_ttl_seconds', fn() => DAY_IN_SECONDS);
add_filter('mtc_max_queued_ui_ms', fn() => 6000);
add_filter('mtc_poll_interval_ms', fn() => 2000);
add_filter('mtc_poll_max_backoff_ms', fn() => 15000);

add_filter('mtc_rate_limit_window_seconds', fn() => 10 * MINUTE_IN_SECONDS);
add_filter('mtc_rate_limit_max_uploads_per_window', fn() => 80);
add_filter('mtc_status_rate_limit_per_batch_window_seconds', fn() => 60);
add_filter('mtc_status_rate_limit_per_batch_per_window', fn() => 240);
add_filter('mtc_status_rate_limit_ip_window_seconds', fn() => 600);
add_filter('mtc_status_rate_limit_ip_per_window', fn() => 1000);

add_filter('mtc_queue_nudge_after_seconds', fn() => 3);
add_filter('mtc_inline_process_after_seconds', fn() => 12);

// ClamAV is disabled by default. Enable it only on hosts with a working clamdscan setup.
add_filter('mtc_clamav_enabled', fn() => true);
add_filter('mtc_clamav_fail_open', fn() => false);
add_filter('mtc_clamdscan_path', fn() => '/usr/bin/clamdscan');
add_filter('mtc_clamav_cmd_timeout_seconds', fn() => 6);
add_filter('mtc_timeout_bin', fn() => '/usr/bin/timeout');

add_filter('mtc_zip_cache_ttl', fn() => 900);
add_filter('mtc_cleanup_days', fn() => 2);

Security Notes

• Nonce-protected AJAX requests (mtc_nonce)
• Signed, expiring download URLs (HMAC with wp_salt('auth'))
• Uploaded files stored in a non-public uploads subdirectory
• Direct-access blocks for Apache/IIS (.htaccess, web.config)
• MIME/header checks plus binary MIDI magic check (MThd)
• Optional AV scanning through clamdscan when enabled

Operational Notes

• This plugin relies on WP-Cron for background processing.
• If your site has low traffic, cron events may fire late.
• Recent changes include queue nudging and inline fallback to reduce long queued waits.

Development

Project layout:

.
├── midi-type0-converter.php         # Main plugin bootstrap + AJAX/cron handlers
├── includes/
│   └── class-mtc-midi-converter.php # Pure PHP MIDI parser/merger
└── assets/
    ├── mtc.js                       # Frontend upload + polling UI
    └── mtc.css                      # Frontend styles

Syntax checks:

php -l midi-type0-converter.php
php -l includes/class-mtc-midi-converter.php
php tests/midi-converter-test.php

License

GPLv2 or later.