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//! Frame pump loops: ADTS and LATM/LOAS iteration over a byte buffer,
//! per-frame caps/consistency ([`Decoder::tally`]), and delivery — either
//! the borrowed-plane callback ([`Decoder::emit`]) or, for one-shot mono,
//! a sink `Vec` the engine appends to directly (no scratch, no copy).
use crate::engine::adts::AdtsHeader;
use crate::engine::bits::BitReader;
use crate::engine::error::Error as EngineError;
use crate::engine::latm::{LOAS_SYNC, MuxCfg, read_payload};
use crate::error::{AacError, Result};
use crate::isomp4::sniff_is_isobmff;
use crate::options::ChannelMode;
use crate::sniff::{sniff_is_adts, sniff_is_latm};
use super::{Container, Decoder, Frame};
impl Decoder {
/// Pump complete frames out of `buf` (starting at `self.pos`). When
/// `sink` is `Some` (one-shot mono), frames decode straight into it and
/// `on_frame` never fires; `est_frames` then pre-sizes the sink after
/// the first frame.
pub(super) fn pump<F>(
&mut self,
buf: &[u8],
sink: Option<&mut Vec<f32>>,
est_frames: Option<usize>,
on_frame: &mut F,
final_flush: bool,
) -> Result<()>
where
F: FnMut(Frame<'_>) -> Result<()>,
{
if matches!(self.container, Container::Unknown) {
let avail = &buf[self.pos..];
if avail.len() < 8 && !final_flush {
return Ok(()); // wait for enough bytes to sniff
}
if sniff_is_isobmff(avail) {
return Err(AacError::format(
"aac: M4A/ISOBMFF needs random access; use decode_streaming",
));
}
// Sniff order and ADTS fallback mirror `decode_with`.
self.container = if sniff_is_adts(avail) || !sniff_is_latm(avail) {
Container::Adts
} else {
Container::Latm
};
}
match self.container {
Container::Adts => self.pump_adts(buf, sink, est_frames, on_frame),
Container::Latm => self.pump_latm(buf, sink, est_frames, on_frame),
Container::Unknown => Ok(()),
}
}
fn pump_adts<F>(
&mut self,
buf: &[u8],
mut sink: Option<&mut Vec<f32>>,
est_frames: Option<usize>,
on_frame: &mut F,
) -> Result<()>
where
F: FnMut(Frame<'_>) -> Result<()>,
{
loop {
let avail = &buf[self.pos..];
let (hdr, payload_off) = match AdtsHeader::parse(avail) {
Ok(v) => v,
// Partial header: wait for more bytes (finish drops it).
Err(EngineError::UnexpectedEnd) => return Ok(()),
// Definite garbage: resync one byte, like the one-shot loop.
Err(_) => {
self.pos += 1;
continue;
}
};
let frame_len = usize::from(hdr.aac_frame_length);
if avail.len() < frame_len {
return Ok(()); // partial frame: wait (finish drops it)
}
let payload = &avail[payload_off..frame_len];
let idx = self.aac_frames;
let rate = match sink.as_deref_mut() {
// One-shot mono: decode straight into the caller's plane.
Some(dst) => {
let before = dst.len();
let rate = self
.dec
.decode_raw_mono_f32(
hdr.audio_object_type(),
hdr.sampling_frequency_index,
hdr.sample_rate(),
hdr.channel_configuration,
hdr.number_of_raw_data_blocks_in_frame,
payload,
dst,
)
.map_err(|e| {
AacError::decode(format!("aac: decode failed at frame {idx}: {e:?}"))
})?;
let n = dst.len() - before;
self.tally(rate, 1, n)?;
if idx == 0 {
self.reserve_hint(dst, est_frames, n);
}
rate
}
None => self.decode_adts(&hdr, payload, idx)?,
};
self.pos += frame_len;
self.aac_frames += 1;
if sink.is_none() {
self.emit(rate, on_frame)?;
}
}
}
/// Decode one ADTS payload: mono fast path into `mono_scratch`, or
/// scaled planes borrowed via `frame_planes`.
fn decode_adts(&mut self, hdr: &AdtsHeader, payload: &[u8], idx: u64) -> Result<u32> {
let (aot, fs, sr, ch) = (
hdr.audio_object_type(),
hdr.sampling_frequency_index,
hdr.sample_rate(),
hdr.channel_configuration,
);
if matches!(self.opts.channel_mode, ChannelMode::Mono) {
self.mono_scratch.clear();
self.dec
.decode_raw_mono_f32(
aot,
fs,
sr,
ch,
hdr.number_of_raw_data_blocks_in_frame,
payload,
&mut self.mono_scratch,
)
.map_err(|e| AacError::decode(format!("aac: decode failed at frame {idx}: {e:?}")))
} else {
self.dec
.decode_frame_scaled(aot, fs, sr, ch, payload)
.map_err(|e| AacError::decode(format!("aac: decode failed at frame {idx}: {e}")))
}
}
fn pump_latm<F>(
&mut self,
buf: &[u8],
mut sink: Option<&mut Vec<f32>>,
est_frames: Option<usize>,
on_frame: &mut F,
) -> Result<()>
where
F: FnMut(Frame<'_>) -> Result<()>,
{
loop {
let avail = &buf[self.pos..];
if avail.len() < 3 {
return Ok(()); // retain the trailing bytes across feeds
}
let v = (u32::from(avail[0]) << 16) | (u32::from(avail[1]) << 8) | u32::from(avail[2]);
if v >> 13 != LOAS_SYNC {
self.pos += 1; // byte-scan resync, like the one-shot loop
continue;
}
let mux_len = (v & 0x1FFF) as usize;
if avail.len() < 3 + mux_len {
return Ok(()); // partial LOAS frame: wait (finish drops it)
}
let body = &avail[3..3 + mux_len];
let mut br = BitReader::new(body);
let use_same = br.read_bit().map_err(AacError::from)?;
if !use_same {
self.mux = Some(MuxCfg::parse(&mut br).map_err(AacError::from)?);
}
let cfg = self
.mux
.as_ref()
.ok_or(EngineError::LatmNoPreviousMuxConfig)
.map_err(AacError::from)?;
let (aot, fs, sr, ch) = (
cfg.asc.aot,
cfg.asc.sampling_frequency_index,
cfg.asc.sample_rate,
cfg.asc.channel_configuration,
);
let payload = read_payload(&mut br, cfg).map_err(AacError::from)?;
let idx = self.aac_frames;
let rate = match sink.as_deref_mut() {
// One-shot mono: decode straight into the caller's plane.
Some(dst) => {
let before = dst.len();
let rate = self
.dec
.decode_raw_mono_f32(aot, fs, sr, ch, 1, &payload, dst)
.map_err(AacError::from)?;
let n = dst.len() - before;
self.tally(rate, 1, n)?;
if idx == 0 {
self.reserve_hint(dst, est_frames, n);
}
rate
}
None => {
if matches!(self.opts.channel_mode, ChannelMode::Mono) {
self.mono_scratch.clear();
self.dec
.decode_raw_mono_f32(
aot,
fs,
sr,
ch,
1,
&payload,
&mut self.mono_scratch,
)
.map_err(AacError::from)?
} else {
self.dec
.decode_frame_scaled(aot, fs, sr, ch, &payload)
.map_err(AacError::from)?
}
}
};
self.pos += 3 + mux_len;
self.aac_frames += 1;
if sink.is_none() {
self.emit(rate, on_frame)?;
}
}
}
/// Caps + consistency for one decoded frame (delivery is the caller's).
fn tally(&mut self, rate: u32, n_ch: usize, n_samples: usize) -> Result<()> {
if n_ch == 0 {
return Ok(()); // channel-less frame: consumed, not emitted
}
match self.locked {
None => {
if rate == 0 || rate > self.opts.max_sample_rate {
return Err(AacError::sample_rate(rate, self.opts.max_sample_rate));
}
self.locked = Some((rate, n_ch));
self.max_samples = self.opts.max_frames(rate);
}
Some((r, c)) => {
if rate != r {
return Err(AacError::decode(format!(
"aac: sample rate changed mid-stream ({r}Hz → {rate}Hz)"
)));
}
if c != n_ch {
return Err(AacError::decode(format!(
"aac: channel count changed mid-stream ({c} → {n_ch})"
)));
}
}
}
self.samples_decoded += n_samples as u64;
if self.samples_decoded > self.max_samples as u64 {
let observed_s = self.samples_decoded as f64 / f64::from(rate.max(1));
return Err(AacError::too_long(observed_s, self.opts.max_duration_secs));
}
self.samples_out += n_samples as u64;
self.emitted += 1;
Ok(())
}
/// Pre-size the mono sink after frame 1: exact frame count × first
/// frame's samples beats geometric growth (hint only, capped).
fn reserve_hint(&self, dst: &mut Vec<f32>, est_frames: Option<usize>, first: usize) {
if let Some(frames) = est_frames {
let want = frames.saturating_mul(first).min(self.max_samples);
dst.reserve(want.saturating_sub(dst.len()));
}
}
/// Caps + consistency for one decoded frame, then the callback.
fn emit<F>(&mut self, rate: u32, on_frame: &mut F) -> Result<()>
where
F: FnMut(Frame<'_>) -> Result<()>,
{
let mono = matches!(self.opts.channel_mode, ChannelMode::Mono);
let (n_ch, n_samples) = if mono {
(1, self.mono_scratch.len())
} else {
let planes = self.dec.frame_planes();
(planes.len(), planes.first().map_or(0, Vec::len))
};
if n_ch == 0 {
return Ok(()); // channel-less frame: consumed, not emitted
}
self.tally(rate, n_ch, n_samples)?;
// Borrow the planes for the duration of the callback only.
let mono_plane: [&[f32]; 1];
let split_planes: Vec<&[f32]>;
let planar: &[&[f32]] = if mono {
mono_plane = [self.mono_scratch.as_slice()];
&mono_plane
} else {
split_planes = self.dec.frame_planes().iter().map(Vec::as_slice).collect();
&split_planes
};
on_frame(Frame {
sample_rate: rate,
samples: n_samples,
planar,
})
}
}