Technical Specification: Native Go DVD/Blu-ray Authoring (VideoTools)

1. Introduction

This document defines the architecture and implementation details for a native Go library to replace DVDauthor, spumux, and xorriso. The goal is a cross-platform, dependency-free solution for generating DVD-Video and Blu-ray compliant images.

2. Architecture Overview

The system is divided into four primary layers, which can be used independently or integrated:

1. VOB Muxer (internal/DVD/vob): Program Stream (PS) muxing with Navigation Packs (NAV_PCK).
2. SPU Encoder (internal/DVD/spu): 2-bit RLE encoding for subpicture (button) overlays.
3. IFO Generator (internal/DVD/ifo): Binary serialization of DVD Management and Title sets.
4. UDF Bridge Writer (internal/DVD/udf): ISO 9660 + UDF 1.02 filesystem generation.

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3. Layer 1: MPEG-PS / VOB Muxer

DVDs use a specific subset of MPEG-2 Program Streams called VOB (Video Object).

3.1 Navigation Packs (NAV_PCK)

Every VOB Unit (VOBU) must start with a NAV_PCK (System Header + PCI + DSI).

• PCI (Presentation Control Information):
  • LVOBU_S_PTM: Start presentation time.
  • LVOBU_E_PTM: End presentation time.
  • HL_GI: Highlight General Information (button coordinates and colors).
• DSI (Data Search Information):
  • VOBU_SRI: Search information for fast-forward/rewind (relative offsets to other VOBUs).
  • VOBU_EA: End address of the current VOBU.

3.2 Stream IDs

• 0xE0: Video Stream (MPEG-2).
• 0xBD: Private Stream 1 (AC3, DTS, or SPU).
• 0xBE: Padding Stream.

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4. Layer 2: SPU Encoder (Subpictures)

Used for menu buttons and subtitles.

4.1 2-bit RLE Encoding

The DVD subpicture format uses 4 colors (Background, Pattern, Emphasis 1, Emphasis 2).

• Encoder Logic:
  1. Downsample 32-bit RGBA overlays to 2-bit indexed color.
  2. Apply RLE: [count][color].
  3. Generate DCSQ (Display Control Sequence) commands:
     • SET_COLOR: Assign colors from the PGC palette.
     • SET_CONTR: Set transparency (Alpha).
     • CHG_COLCON: Change color/contrast for button highlights.

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5. Layer 3: IFO/BUP Generation

IFO files are the "brains" of the DVD. They use a strict table-based binary format.

5.1 Required Tables

• VMGI (Video Manager Information): VIDEO_TS.IFO
  • TT_SRPT: Title Search Pointer Table (maps titles to VTS).
  • PGCI_UT: PGC Unit Table (Menu navigation).
• VTSI (Video Title Set Information): VTS_01_0.IFO
  • VTS_ATTRIBUTES: Video/Audio/Subpicture attributes.
  • VTS_PGCITI: Program Chain Information Table (Chapters and Playback order).
  • VTS_VOBU_ADMAP: Sector addresses of every NAV_PCK in the VOB set.

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6. Layer 4: UDF 1.02 / ISO 9660 Bridge

To be playable on hardware, the ISO must be a "Bridge" disc.

6.1 UDF 1.02 Requirements

• Sector Size: 2048 bytes (Strict).
• Alignment: VIDEO_TS.IFO and VIDEO_TS.BUP must be in different ECC blocks (usually handled by 32KB+ spacing) to ensure recovery if a sector is damaged.
• Anchor Volume Descriptor: Must be at sector 256.
• Metadata: Implementation of ECMA-167 for File Entry (ICB) and File Identifier Descriptors.

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7. Data Flow Integration in VideoTools

1. Input: User selects clips and defines menu in Author Module.
2. Transcode: FFmpeg generates raw .m2v (Video) and .ac3 (Audio).
3. Menu Gen:
   • spu.Encode() generates .sub binary from PNG buttons.
   • vob.Mux() creates menu.vob with NAV_PCKs containing button highlights.
4. Authoring:
   • vob.Mux() joins clips into VTS_01_1.VOB ... VTS_01_N.VOB.
   • ifo.Generate() scans VOBs to build VTS_01_0.IFO and VIDEO_TS.IFO.
5. Mastering:
   • udf.Write() takes the VIDEO_TS folder and produces the final .iso.

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8. Standalone Capability

The library will be structured as a Go Module (github.com/leak_technologies/go-DVDauthor) with a clean API:

// Example Standalone Usage
author := DVD.NewAuthor("output/")
author.AddTitle(videoPath, audioPath, chapters)
author.SetMenu(backgroundMPEG, buttons)
err := author.Build()
err = udf.CreateISO("DVD.iso", "output/")

9. Validation Strategy

1. Binary Comparison: Compare generated IFO headers against DVDauthor output.
2. Structural Validation: Use DVDisaster or ifodump to verify table integrity.
3. Hardware Emulation: Validate ISOs in VLC and specialized DVD players (PowerDVD/MPC-HC) to ensure menu navigation works.