Add JAR parser: extract audio/subtitle labels from BD-J menus
Scans BDMV/JAR/*.jar class files for track label patterns: eng_MLP_ → TrueHD, eng_ADES_US_ → Descriptive Audio (US) dan_PGStream4 → Danish subtitles Solves the "3x AC-3 English" problem — we identify Descriptive Audio, commentary, compatibility tracks. Future: set MKV "visual impaired" flag automatically during mux. Local only — needs more disc samples to validate before publishing.
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MattJackson
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//! BD-J JAR parser — extract audio/subtitle track labels from disc menus.
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//!
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//! Blu-ray discs with BD-J menus store the menu application as Java JAR files
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//! in BDMV/JAR/. These contain .class files with string constants that label
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//! audio and subtitle tracks (e.g. "eng_ADES_US_" = Descriptive Audio US).
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//!
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//! with no way to tell them apart (e.g. 3x "AC-3 5.1 English").
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//!
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//! The JAR is a ZIP file. Each .class file has a Java constant pool containing
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//! UTF-8 string literals. We scan for patterns like:
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//! {lang}_{codec}_{variant}_ → audio track labels
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//! {lang}_PGStream{n} → subtitle track labels
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//! MAIN_FEATURE → playlist identification
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//! FORCED_TRAILER → forced content identification
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//!
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//! This is best-effort: if the JAR doesn't contain labels or the format
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//! is unexpected, we return empty results. The caller falls back to
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//! showing streams without labels.
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use std::io::Read;
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/// Labels extracted from a BD-J JAR file.
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#[derive(Debug, Default)]
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pub struct JarLabels {
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/// Audio track labels in STN order: (language, codec_hint, variant, raw_label)
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pub audio: Vec<TrackLabel>,
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/// Subtitle track labels: (language, stream_index, raw_label)
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pub subtitle: Vec<TrackLabel>,
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/// Playlist purpose labels (MAIN_FEATURE, FORCED_TRAILER, etc.)
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pub playlists: Vec<String>,
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}
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/// A parsed track label from the JAR.
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#[derive(Debug, Clone)]
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pub struct TrackLabel {
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/// ISO 639-2 language code (e.g. "eng", "fra")
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pub language: String,
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/// Codec or type hint (e.g. "MLP", "AC3", "ADES", "PGStream")
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pub hint: String,
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/// Variant or region (e.g. "US", "UK", "3", "4")
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pub variant: String,
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/// Human-readable description derived from the label
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pub description: String,
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/// The raw string from the class file
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pub raw: String,
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}
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impl TrackLabel {
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/// Parse a label string like "eng_ADES_US_" or "dan_PGStream4"
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fn parse(s: &str) -> Option<Self> {
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let clean = s.trim_end_matches('_');
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let parts: Vec<&str> = clean.splitn(3, '_').collect();
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if parts.len() < 2 {
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return None;
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}
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let language = parts[0].to_string();
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// Language should be 2-3 lowercase letters
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if language.len() < 2 || language.len() > 3 || !language.chars().all(|c| c.is_ascii_lowercase()) {
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return None;
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}
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let hint = parts[1].to_string();
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let variant = if parts.len() > 2 { parts[2].to_string() } else { String::new() };
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let description = match hint.as_str() {
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"MLP" => "TrueHD".to_string(),
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"AC3" => {
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if variant.is_empty() { "compatibility".to_string() }
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else { variant.clone() }
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}
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"DTS" => "DTS".to_string(),
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"LPCM" => "LPCM".to_string(),
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"ADES" => {
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if variant.is_empty() { "Descriptive Audio".to_string() }
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else { format!("Descriptive Audio ({})", variant) }
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}
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h if h.starts_with("AudioStream") => String::new(), // generic, no extra info
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h if h.starts_with("PGStream") => String::new(), // generic subtitle
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_ => String::new(),
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};
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Some(TrackLabel {
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language,
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hint,
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variant,
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description,
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raw: s.to_string(),
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})
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}
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/// Is this an audio track label?
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fn is_audio(&self) -> bool {
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matches!(self.hint.as_str(), "MLP" | "AC3" | "DTS" | "LPCM" | "ADES")
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|| self.hint.starts_with("AudioStream")
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}
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/// Is this a subtitle track label?
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fn is_subtitle(&self) -> bool {
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self.hint.starts_with("PGStream")
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}
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}
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/// Extract track labels from a JAR file (raw ZIP bytes).
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///
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/// Returns None if the JAR can't be parsed or contains no labels.
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/// This is best-effort — failure is not an error.
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pub fn extract_labels(jar_data: &[u8]) -> Option<JarLabels> {
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let cursor = std::io::Cursor::new(jar_data);
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let mut archive = zip::ZipArchive::new(cursor).ok()?;
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let mut all_audio = Vec::new();
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let mut all_subtitle = Vec::new();
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let mut all_playlists = Vec::new();
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for i in 0..archive.len() {
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let mut file = archive.by_index(i).ok()?;
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if !file.name().ends_with(".class") {
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continue;
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}
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let mut data = Vec::new();
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file.read_to_end(&mut data).ok()?;
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let strings = extract_class_strings(&data);
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for s in &strings {
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// Track labels: {lang}_{type}_{variant}_
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if let Some(label) = TrackLabel::parse(s) {
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if label.is_audio() && !all_audio.iter().any(|a: &TrackLabel| a.raw == label.raw) {
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all_audio.push(label);
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} else if label.is_subtitle() && !all_subtitle.iter().any(|a: &TrackLabel| a.raw == label.raw) {
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all_subtitle.push(label);
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}
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}
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// Playlist purpose labels
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if matches!(s.as_str(),
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"MAIN_FEATURE" | "MAIN_FEATURE_INTRO" |
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"FORCED_TRAILER" | "INTL_FORCED_TRAILER" |
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"commentary_extras" | "extras"
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) {
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if !all_playlists.contains(s) {
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all_playlists.push(s.clone());
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}
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}
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}
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}
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if all_audio.is_empty() && all_subtitle.is_empty() {
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return None;
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}
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Some(JarLabels {
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audio: all_audio,
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subtitle: all_subtitle,
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playlists: all_playlists,
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})
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}
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/// Extract all UTF-8 string constants from a Java .class file's constant pool.
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///
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/// Java class file format:
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/// [0:4] magic (0xCAFEBABE)
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/// [4:6] minor version
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/// [6:8] major version
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/// [8:10] constant_pool_count
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/// [10:] constant_pool entries
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///
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/// CONSTANT_Utf8 (tag=1): u8 tag + u16 length + bytes
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/// We only extract these — they contain all string literals.
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fn extract_class_strings(data: &[u8]) -> Vec<String> {
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let mut strings = Vec::new();
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// Verify Java class magic
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if data.len() < 10 || &data[0..4] != &[0xCA, 0xFE, 0xBA, 0xBE] {
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return strings;
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}
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let cp_count = ((data[8] as u16) << 8 | data[9] as u16) as usize;
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let mut pos = 10;
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// Parse constant pool entries
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let mut entry = 1; // constant pool is 1-indexed
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while entry < cp_count && pos < data.len() {
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let tag = data[pos];
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pos += 1;
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match tag {
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// CONSTANT_Utf8
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1 => {
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if pos + 2 > data.len() { break; }
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let len = ((data[pos] as usize) << 8) | data[pos + 1] as usize;
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pos += 2;
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if pos + len > data.len() { break; }
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if let Ok(s) = std::str::from_utf8(&data[pos..pos + len]) {
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// Only keep strings that look like track labels
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// Must contain underscore and be reasonable length
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if s.len() >= 5 && s.len() <= 100 && s.contains('_') {
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strings.push(s.to_string());
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}
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}
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pos += len;
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}
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// CONSTANT_Integer, CONSTANT_Float
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3 | 4 => { pos += 4; }
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// CONSTANT_Long, CONSTANT_Double (take 2 entries)
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5 | 6 => { pos += 8; entry += 1; }
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// CONSTANT_Class, CONSTANT_String, CONSTANT_MethodType
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7 | 8 | 16 => { pos += 2; }
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// CONSTANT_Fieldref, CONSTANT_Methodref, CONSTANT_InterfaceMethodref,
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// CONSTANT_NameAndType, CONSTANT_InvokeDynamic
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9 | 10 | 11 | 12 | 18 => { pos += 4; }
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// CONSTANT_MethodHandle
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15 => { pos += 3; }
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// Unknown tag — can't continue parsing safely
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_ => { break; }
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}
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entry += 1;
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}
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strings
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_parse_audio_labels() {
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let l = TrackLabel::parse("eng_MLP_").unwrap();
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assert_eq!(l.language, "eng");
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assert_eq!(l.hint, "MLP");
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assert_eq!(l.description, "TrueHD");
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assert!(l.is_audio());
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let l = TrackLabel::parse("eng_ADES_US_").unwrap();
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assert_eq!(l.language, "eng");
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assert_eq!(l.hint, "ADES");
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assert_eq!(l.variant, "US");
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assert_eq!(l.description, "Descriptive Audio (US)");
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assert!(l.is_audio());
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let l = TrackLabel::parse("fra_AudioStream3").unwrap();
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assert_eq!(l.language, "fra");
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assert!(l.is_audio());
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}
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#[test]
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fn test_parse_subtitle_labels() {
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let l = TrackLabel::parse("dan_PGStream4").unwrap();
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assert_eq!(l.language, "dan");
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assert!(l.is_subtitle());
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}
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#[test]
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fn test_reject_non_labels() {
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assert!(TrackLabel::parse("substring").is_none());
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assert!(TrackLabel::parse("equals").is_none());
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assert!(TrackLabel::parse("Code").is_none());
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}
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}
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