makepad/libs/game/audio/examples/vorbis_align.rs
Admin 62d6732504 Vorbis: mono decodes sample-exact (115/160 files exact, was 0)
Two root causes, both found by building an oracle rather than guessing.

1. Amplitude ~75x low: the IMDCT applied a 2/n normalisation the encoder's
   forward transform had already carried. Because 2/n varies with block size
   it produced DIFFERENT errors on 256- vs 2048-sample blocks — exactly the
   reported symptom. Removing it gives fit scale 1.0000.

2. Leading trim, the real remaining defect. The first audio packet produces NO
   output (its window only primes the overlap-add) but we emitted from the
   first block's centre, injecting half a priming window of garbage and
   shifting everything early. And Vorbis carries encoder delay in the GRANULE
   POSITION, which varies per file — afinfo confirms 128 / 1103 / 960 frames
   on three samples — while our Ogg reader kept only last_granule and
   discarded per-page granules, making it unrecoverable. Added per-page
   granule tracking: the first page reporting a granule pins priming as
   centre - granule, and valid audio starts at priming + blocksize_0/2. That
   reproduces afinfo's numbers exactly on all three.

A premise in the brief was also wrong and worth recording: our output length
was already correct. afinfo reports valid frames matching OUR output — it is
afconvert that trims a further 128. The reference WAV was short, not us.

  mono    47 files  mean corr 1.00000 (min 1.00000)  47/47 exact
  stereo 107 files  mean corr 0.826                  68/107 exact

Decode cost 5.13 ms/file average; 11.5 MB compressed expands to 143.3 MB of
f32 PCM, which is why the sample bank's LRU cap matters.

Honest remaining defect: ~39 stereo files decode wrongly and it is NOT
alignment — a full lag sweep peaks at 0.40-0.89 with fit scales 0.40-1.87, so
specific blocks have wrong amplitude. Mono being 47/47 rules out floor,
residue 0/1, MDCT, windowing and priming; coupling matches the spec's
square-polar mapping including reverse order; floor 0 is rejected rather than
mis-decoded; and both channels are identical in the failing files, so it is
not a swap. The failing set is transient-heavy impact/footstep sounds, so the
lead is residue type 2 partition counting on short blocks.

reference_decode.rs is no longer #[ignore]d: 3 real tests asserting mono
correlation > 0.999 and length == granule, plus a 3000-mutation fuzz that must
never panic, all skipping cleanly without fixtures.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-08-03 09:26:27 +02:00

78 lines
2.9 KiB
Rust

//! Correlate block geometry against the true start offset, so the lapping
//! rule is derived from data instead of guessed.
//! Usage: vorbis_align <dir> <tmp> [limit]
use makepad_game_audio as audio;
use std::process::Command;
fn best_lag(g: &[f32], w: &[f32], ch: usize) -> (i64, f64) {
let n = g.len().min(w.len());
let mut best = (0i64, 0f64);
// Lags are whole frames; step by channel count so stereo isn't tested
// at half-frame offsets that can never be right.
let step = ch as i64;
let mut lag = -8192i64;
while lag <= 8192 {
let (mut num, mut dg, mut dw) = (0f64, 0f64, 0f64);
let mut i = 0usize;
while i < n {
let j = i as i64 + lag;
if j >= 0 && (j as usize) < n {
let (a, b) = (g[i] as f64, w[j as usize] as f64);
num += a * b;
dg += a * a;
dw += b * b;
}
i += 16; // sparse sample: enough to find the peak, 16x faster
}
if dg > 0.0 && dw > 0.0 {
let c = num / (dg.sqrt() * dw.sqrt());
if c > best.1 {
best = (lag, c);
}
}
lag += step;
}
best
}
fn main() {
let a: Vec<String> = std::env::args().collect();
let (dir, tmp) = (&a[1], &a[2]);
let limit: usize = a.get(3).and_then(|s| s.parse().ok()).unwrap_or(20);
let mut files = walk(dir);
files.sort();
println!("{:>4} {:>5} {:>5} {:>8} {:>8} {:>7} {:>7} file", "ch", "n0", "n1", "granule", "reflen", "lagfrm", "corr");
let mut done = 0;
for f in files.iter() {
if done >= limit { break }
let refwav = format!("{tmp}/align_ref.wav");
let _ = std::fs::remove_file(&refwav);
if !matches!(Command::new("afconvert").args(["-f","WAVE","-d","LEF32",f,&refwav]).status(), Ok(s) if s.success()) { continue }
let (Ok(o), Ok(wv)) = (std::fs::read(f), std::fs::read(&refwav)) else { continue };
let Ok(got) = audio::decode(&o) else { continue };
let Ok(want) = audio::wav::decode(&wv) else { continue };
done += 1;
let (lag, c) = best_lag(&got.samples, &want.samples, got.channels);
let bs = audio::debug_block_sizes(&o).unwrap_or_default();
let name = f.rsplit('/').next().unwrap_or(f);
println!("{:>4} {:>5} {:>5} {:>8} {:>8} {:>7} {:>7.4} {}",
got.channels,
bs.first().copied().unwrap_or(0),
bs.get(1).copied().unwrap_or(0),
got.frames(),
want.frames(),
-lag / got.channels as i64,
c, name);
}
}
fn walk(dir: &str) -> Vec<String> {
let mut out = Vec::new();
let Ok(rd) = std::fs::read_dir(dir) else { return out };
for e in rd.flatten() {
let p = e.path();
if p.is_dir() { out.extend(walk(&p.to_string_lossy())) }
else if p.extension().map(|x| x == "ogg").unwrap_or(false) { out.push(p.to_string_lossy().into_owned()) }
}
out
}