Sylpheed/crates/sylpheed-formats/examples/slb_fmt_probe.rs

//! Does the `.slb` leading region decode as XMA1 under ANY plausible format?
//!
//! A first attempt at this hand-rolled the `fmt ` chunk and produced 0 PCM bytes
//! for all 36 combinations — including ones that should have matched the crate's
//! own working format. So it tested the chunk construction, not the hypothesis.
//! This version replicates `slb::synth_xma1_fmt`'s exact byte layout and starts
//! by reproducing its known result as a CONTROL; if the control does not match,
//! nothing below it means anything.
use std::io::Write;
use std::process::{Command, Stdio};

use sylpheed_formats::{movie_subtitle, slb, PakArchive};

/// Byte-for-byte `slb::synth_xma1_fmt` (private there). Note the second
/// parameter is a **channel mask**, not a stream count — mistaking it is what
/// made the first probe meaningless.
fn xma1_fmt(channels: u8, channel_mask: u16, rate: u32) -> Vec<u8> {
    let mut fmt = Vec::with_capacity(40);
    fmt.extend_from_slice(b"fmt ");
    fmt.extend_from_slice(&32u32.to_le_bytes());
    fmt.extend_from_slice(&0x0165u16.to_le_bytes()); // XMA1
    fmt.extend_from_slice(&16u16.to_le_bytes()); // BitsPerSample
    fmt.extend_from_slice(&0u16.to_le_bytes()); // EncodeOptions
    fmt.extend_from_slice(&0u16.to_le_bytes()); // LargestSkip
    fmt.extend_from_slice(&1u16.to_le_bytes()); // NumStreams
    fmt.push(0); // LoopCount
    fmt.push(3); // Version
    fmt.extend_from_slice(&(rate * channels as u32 * 2).to_le_bytes());
    fmt.extend_from_slice(&rate.to_le_bytes());
    fmt.extend_from_slice(&0u32.to_le_bytes());
    fmt.extend_from_slice(&0u32.to_le_bytes());
    fmt.push(4); // SubframeData
    fmt.push(channels);
    fmt.extend_from_slice(&channel_mask.to_le_bytes());
    fmt
}

fn riff(fmt: &[u8], data: &[u8]) -> Vec<u8> {
    let mut out = Vec::with_capacity(12 + fmt.len() + 8 + data.len());
    out.extend_from_slice(b"RIFF");
    out.extend_from_slice(&((4 + fmt.len() + 8 + data.len()) as u32).to_le_bytes());
    out.extend_from_slice(b"WAVE");
    out.extend_from_slice(fmt);
    out.extend_from_slice(b"data");
    out.extend_from_slice(&(data.len() as u32).to_le_bytes());
    out.extend_from_slice(data);
    out
}

fn decode_bytes(r: &[u8]) -> usize {
    let Ok(mut c) = Command::new("ffmpeg")
        .args(["-v", "error", "-i", "pipe:0", "-f", "s16le", "pipe:1"])
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::null())
        .spawn()
    else {
        return 0;
    };
    let buf = r.to_vec();
    let mut stdin = c.stdin.take().unwrap();
    std::thread::spawn(move || {
        let _ = stdin.write_all(&buf);
    });
    c.wait_with_output().map(|o| o.stdout.len()).unwrap_or(0)
}

fn main() {
    let disc = std::env::var("SYLPHEED_DISC").expect("set SYLPHEED_DISC");
    let snd = PakArchive::open(format!("{disc}/dat/sound.pak")).expect("sound.pak");
    let lang = PakArchive::open(format!("{disc}/dat/movie/eng.pak")).expect("eng.pak");

    // The leading region decodes only as MONO. At channels=2 it yields 1792
    // bytes; at channels=1, 203648 for VOICE_D_453. The decoded SAMPLE COUNT is
    // independent of the declared rate (the rate only sets playback speed), so
    // the subtitle cue can be used to solve for the real rate instead.
    let bound = [
        ("hokyu_LS_s02A", 450u32),
        ("hokyu_LS_s09A", 451),
        ("hokyu_DS_s13A", 452),
        ("hokyu_LS_s02H", 453),
        ("hokyu_DS_s07H", 454),
    ];
    println!(
        "{:<16} {:>6} {:>9} {:>9} {:>10} {:>9} {:>12}",
        "movie", "bank", "stereo B", "mono B", "samples", "cue s", "implied Hz"
    );
    for (movie, n) in bound {
        let path = format!("eng\\etc\\VOICE_D_{n}.slb");
        let Some(entry) = snd.find_by_name(&path) else {
            continue;
        };
        let bytes = snd.read(entry).expect("read");
        let Some(first_riff) = bytes.windows(4).position(|w| w == b"RIFF") else {
            continue;
        };
        if first_riff <= slb::HEADERLESS_DATA_OFFSET {
            println!("{movie:<16} {:>6}   (no leading region)", format!("D_{n}"));
            continue;
        }
        let lead = &bytes[slb::HEADERLESS_DATA_OFFSET..first_riff];
        let stereo = decode_bytes(&riff(&xma1_fmt(2, 2, 48000), lead));
        let mono = decode_bytes(&riff(&xma1_fmt(1, 0, 48000), lead));
        let samples = mono / 2; // 16-bit mono
        let cue = movie_subtitle::track_voice_cues(&lang, movie)
            .iter()
            .map(|(_, t)| *t)
            .fold(0.0f32, f32::max);
        let implied = if cue > 0.0 {
            samples as f32 / cue
        } else {
            f32::NAN
        };
        println!(
            "{movie:<16} {:>6} {stereo:>9} {mono:>9} {samples:>10} {cue:>9.2} {implied:>12.0}",
            format!("D_{n}")
        );
    }
    println!("\n'implied Hz' = decoded samples / the movie's last subtitle cue.");
    println!("A consistent value near a standard rate is the real sample rate.");
}