wip(3d): read-only 3D-structure probe (SSIF/m2ts + MPLS ExtensionData)

Dev tool for the 3D build: uses the library UDF reader (7z cannot parse these
ISOs) to dump base .m2ts vs SSIF sizes and the MPLS ExtensionData entries
(STN_table_SS + SS sub-path). Not product code.

examples/probe3d_struct.rs

@@ -0,0 +1,82 @@
+// Read-only 3D structure probe: does the disc carry a dependent (MVC) view,
+// where, and how is it described? Uses freemkv's own UDF reader (7z can't parse
+// these ISOs).  probe3d_struct <iso> [clip=00098]
+
+use libfreemkv::sector::SectorSource;
+use libfreemkv::{FileSectorSource, read_filesystem};
+use std::path::Path;
+
+fn be16(b: &[u8], o: usize) -> u16 {
+    u16::from_be_bytes([b[o], b[o + 1]])
+}
+fn be32(b: &[u8], o: usize) -> u32 {
+    u32::from_be_bytes([b[o], b[o + 1], b[o + 2], b[o + 3]])
+}
+
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+    let iso = &args[1];
+    let clip = args.get(2).map(|s| s.as_str()).unwrap_or("00098");
+    let mut r = FileSectorSource::open(Path::new(iso)).expect("open iso");
+    let fs = read_filesystem(&mut r).expect("read udf");
+
+    // Base view vs dependent-interleave file.
+    for (label, path) in [
+        ("base .m2ts", format!("/BDMV/STREAM/{clip}.m2ts")),
+        ("SSIF", format!("/BDMV/STREAM/SSIF/{clip}.ssif")),
+    ] {
+        match fs.file_extents(&mut r, &path) {
+            Ok(exts) => {
+                let sectors: u64 = exts.iter().map(|(_, c)| *c as u64).sum();
+                println!(
+                    "{label:<11}: EXISTS  {:>5} extents  {:>7.2} GB   {path}",
+                    exts.len(),
+                    sectors as f64 * 2048.0 / 1e9
+                );
+            }
+            Err(_) => println!("{label:<11}: MISSING                          {path}"),
+        }
+    }
+
+    // MPLS ExtensionData → the 3D STN_table_SS lives here.
+    let mpls = match fs.read_file(&mut r, &format!("/BDMV/PLAYLIST/{clip}.mpls")) {
+        Ok(m) => m,
+        Err(e) => {
+            println!("\nmpls read failed: {e}");
+            return;
+        }
+    };
+    println!("\nmpls: {} bytes", mpls.len());
+    let ext_addr = be32(&mpls, 16) as usize; // ExtensionData_start_address
+    if ext_addr == 0 || ext_addr + 12 > mpls.len() {
+        println!("ExtensionData_start_address = {ext_addr}  → NO extension data (not a 3D/SS playlist)");
+        return;
+    }
+    let ed = &mpls[ext_addr..];
+    let ed_len = be32(ed, 0) as usize;
+    let n_entries = ed[11] as usize; // len(4)+data_block_start(4)+reserved(3)+count(1)
+    println!("ExtensionData @ {ext_addr}: length={ed_len}  entries={n_entries}");
+    for i in 0..n_entries {
+        let o = 12 + i * 12;
+        if o + 12 > ed.len() {
+            break;
+        }
+        let id1 = be16(ed, o);
+        let id2 = be16(ed, o + 2);
+        let addr = be32(ed, o + 4) as usize; // relative to MPLS file start
+        let len = be32(ed, o + 8) as usize;
+        let tag = match (id1, id2) {
+            (1, 1) => "PiP metadata",
+            (1, 2) => "SubPath entries (SS)",
+            (2, 1) => "STN_table_SS?",
+            (2, 2) => "STN_table_SS (MVC dependent view)",
+            _ => "?",
+        };
+        print!("  entry {i}: ID1={id1:#06x} ID2={id2:#06x} addr={addr} len={len}  [{tag}]  hex:");
+        let blk = &mpls[addr.min(mpls.len())..(addr + 40).min(mpls.len())];
+        for b in blk {
+            print!(" {b:02x}");
+        }
+        println!();
+    }
+}