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//! Windowed / VAD-region word decode for [`Engine`].
use super::*;
impl Engine {
/// Decode a 16 kHz f32 buffer to words: single-pass for short inputs (one
/// encoder Run over the whole buffer), chunked overlapping windows for long
/// inputs so encoder activation memory stays O(chunk), not O(file). Both
/// paths produce the same `Vec<WordInfo>` shape. This is the no-VAD path and
/// the per-region decode used by [`Engine::decode_speech_regions`].
///
/// `biaser` is the effective hotword biaser for this call (engine boot
/// biaser, a temporary per-request biaser, or `None` when forced off).
pub(crate) fn decode_words(
&self,
samples: &[f32],
triplet: &mut SessionTriplet,
biaser: Option<&bias::Biaser>,
ctl: DecodeControls,
) -> Result<Vec<WordInfo>, GigasttError> {
let spec = window_spec(self.ane_encoder, self.variant.is_ctc());
if spec.is_single_pass(samples.len()) {
// A single-pass decode is one encoder Run with no window loop to
// check between, so honour cancellation before starting it. The
// caller's watchdog treats this whole clip as one "window".
if ctl.aborted() {
return Err(GigasttError::Cancelled);
}
let (features, num_frames) = self.features.compute(samples);
tracing::info!("Extracted {} mel frames", num_frames);
let mut decoder_state = DecoderState::new(self.tokenizer.blank_id());
let words = self
.run_inference(
triplet,
&features,
num_frames,
&mut decoder_state,
0,
false, // file-mode fill floor
biaser,
)
.map_err(|e| GigasttError::Inference { source: e.into() })?
.0;
ctl.report(samples.len() as u64);
Ok(words)
} else {
tracing::info!(
"Long-form chunked decode: {:.1}s in ~{}s windows ({}s overlap, ane={})",
samples.len() as f64 / 16000.0,
spec.window() / 16000,
spec.overlap() / 16000,
self.ane_encoder,
);
self.decode_words_streaming(&mut SliceWindows::new(samples, spec), triplet, biaser, ctl)
}
}
/// Decode only the VAD-detected speech `regions` of `float_samples`: copy the
/// speech spans into one silence-free buffer, decode it, then remap each
/// word's start/end from the compressed (silence-removed) timeline back to
/// the original timeline via [`crate::vad::remap_compressed_seconds`]. Empty
/// `regions` (no speech) yields no words.
pub(crate) fn decode_speech_regions(
&self,
float_samples: &[f32],
regions: &[(usize, usize)],
triplet: &mut SessionTriplet,
biaser: Option<&bias::Biaser>,
ctl: DecodeControls,
) -> Result<Vec<WordInfo>, GigasttError> {
if regions.is_empty() {
tracing::info!("VAD found no speech; skipping decode");
return Ok(Vec::new());
}
let speech_len: usize = regions.iter().map(|(s, e)| e - s).sum();
let mut speech = Vec::with_capacity(speech_len);
for &(s, e) in regions {
speech.extend_from_slice(&float_samples[s..e]);
}
tracing::info!(
"VAD kept {}/{} samples ({} speech region(s))",
speech_len,
float_samples.len(),
regions.len()
);
let mut words = self.decode_words(&speech, triplet, biaser, ctl)?;
for w in &mut words {
w.start = crate::vad::remap_compressed_seconds(w.start, regions, 16000.0);
w.end = crate::vad::remap_compressed_seconds(w.end, regions, 16000.0);
}
Ok(words)
}
/// Long-form decode: pull overlapping windows from `windows`, encode and
/// decode each independently with a fresh [`DecoderState`], offset each
/// chunk's word timestamps by the chunk's absolute start, then stitch the
/// per-chunk word lists with overlap de-dup via [`stitch_chunk_words`].
///
/// Peak encoder activation memory is bounded by the source's window length
/// (24s ort / 30s ANE, see [`super::windows::chunk_window_samples`]) rather than the full
/// file length. Window starts are aligned to encoder frame boundaries
/// (multiples of `HOP_LENGTH * ENCODER_SUBSAMPLING`) so the per-chunk frame
/// offset is exact, matching the streaming path's math.
///
/// Takes the PCM as a [`PcmWindows`] source rather than a `&[f32]`, so the
/// loop makes no assumption that the whole file is in memory.
pub(crate) fn decode_words_streaming(
&self,
windows: &mut dyn PcmWindows,
triplet: &mut SessionTriplet,
biaser: Option<&bias::Biaser>,
ctl: DecodeControls,
) -> Result<Vec<WordInfo>, GigasttError> {
let overlap = windows.spec().overlap();
let frame_samples = HOP_LENGTH * ENCODER_SUBSAMPLING;
let mut merged: Vec<WordInfo> = Vec::new();
while let Some(window) = windows.next_window()? {
// Cooperative cancellation checkpoint: a flipped abort flag ends the
// run at this window boundary, so a cancelled request (client
// disconnect, `DELETE /v1/jobs/{id}`, shutdown, or the no-progress
// watchdog) frees its pooled session within one window instead of
// decoding the rest of the file.
if ctl.aborted() {
return Err(GigasttError::Cancelled);
}
let start = window.start_sample;
// Window ends advance monotonically, so this doubles as the
// cumulative processed-sample count reported below.
let win_end = start + window.samples.len();
let (features, num_frames) = self.features.compute(window.samples);
let frame_offset = start / frame_samples;
let mut decoder_state = DecoderState::new(self.tokenizer.blank_id());
let (chunk_words, _endpoint) = self
.run_inference(
triplet,
&features,
num_frames,
&mut decoder_state,
frame_offset,
false, // file-mode fill floor
biaser,
)
.map_err(|e| GigasttError::Inference { source: e.into() })?;
// Seam between the previous chunk's window and this one falls at the
// midpoint of their overlap region, in absolute seconds.
let overlap_mid_s = (start as f64 + overlap as f64 / 2.0) / 16000.0;
merged = stitch_chunk_words(merged, chunk_words, overlap_mid_s);
// A completed window is one unit of real progress: it resets the
// server's no-progress deadline and advances a job's bar by the
// seconds of audio just decoded (`win_end / 16000`).
ctl.report(win_end as u64);
}
Ok(merged)
}
/// Decode a 16 kHz f32 buffer to words, applying VAD if configured.
///
/// The VAD path is taken only when a VAD is attached AND the caller hasn't
/// opted out via `overrides.vad`. `?vad=false` forces whole-buffer decode
/// even on a VAD-enabled engine; `None` uses the engine default (VAD path
/// iff a VAD is attached). `vad = Some(true)` on a VAD-less engine can't
/// reach here — callers should validate overrides first — but the
/// `self.vad.is_some()` guard keeps this correct regardless.
///
/// Hotword selection via `hotwords`:
/// - `None` → engine boot biaser
/// - `Some(empty)` → force biasing off
/// - `Some(phrases)` → temporary biaser built for this request only
pub(crate) fn decode_words_for_samples(
&self,
float_samples: &[f32],
triplet: &mut SessionTriplet,
overrides: &TranscribeOverrides,
hotwords: Option<&HotwordOverride>,
ctl: DecodeControls,
) -> Result<Vec<WordInfo>, GigasttError> {
// Temporary biaser only when the request supplies hotwords. Owned
// here so the `Option<&Biaser>` passed into decode stays valid for
// the whole call without cloning the engine's boot biaser.
let request_biaser = hotwords.and_then(|hw| self.build_request_biaser(hw));
let biaser = self.select_biaser(hotwords, &request_biaser);
let use_vad = self.vad.is_some() && overrides.vad.unwrap_or(true);
match (use_vad, &self.vad) {
(true, Some(vad)) => {
match vad.speech_regions_with_abort(float_samples, &self.vad_config, ctl.abort) {
Ok(regions) if regions.is_empty() => {
// Tone / continuous speech can yield zero regions on a bad
// threshold; fall back to fixed-window / full decode rather
// than returning an empty transcript.
tracing::warn!(
"VAD found no speech regions; falling back to full/chunked decode"
);
self.decode_words(float_samples, triplet, biaser, ctl)
}
Ok(regions) => {
self.decode_speech_regions(float_samples, ®ions, triplet, biaser, ctl)
}
Err(e) => {
// A flipped abort flag stops the VAD scan too; surface it
// as cancellation instead of silently re-decoding the whole
// file, which would ignore the cancel and keep the triplet.
if ctl.aborted() {
return Err(GigasttError::Cancelled);
}
tracing::warn!("VAD failed, decoding full audio: {e:#}");
self.decode_words(float_samples, triplet, biaser, ctl)
}
}
}
_ => self.decode_words(float_samples, triplet, biaser, ctl),
}
}
}