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//! `ics_info()` — ISO/IEC 14496-3 §4.4.6 Table 4.6.
use super::bits::BitReader;
use super::error::{Error, Result};
use super::swb::{long_offsets, short_offsets};
/// `window_sequence` — Table 4.128.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
pub enum WindowSequence {
/// One 2048-point transform.
OnlyLong = 0,
/// Long transform, start window on the right half.
LongStart = 1,
/// Eight 256-point transforms.
EightShort = 2,
/// Long transform, stop window on the left half.
LongStop = 3,
}
impl WindowSequence {
fn from_bits(bits: u8) -> Self {
match bits & 3 {
0 => Self::OnlyLong,
1 => Self::LongStart,
2 => Self::EightShort,
_ => Self::LongStop,
}
}
/// `true` ⇔ eight short windows.
#[must_use]
pub fn is_eight_short(self) -> bool {
matches!(self, Self::EightShort)
}
}
/// `window_shape` — 0 sine, 1 KBD (§4.5.2.3.1.1).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
pub enum WindowShape {
/// Sine window.
Sine = 0,
/// Kaiser-Bessel-derived window.
Kbd = 1,
}
impl WindowShape {
fn from_bit(bit: bool) -> Self {
if bit { Self::Kbd } else { Self::Sine }
}
}
/// Parsed `ics_info()` plus derived grouping.
#[derive(Debug, Clone, Copy)]
pub struct IcsInfo {
/// Table 4.128 window sequence.
pub window_sequence: WindowSequence,
/// This block's right-half shape (left half comes from the previous block).
/// On the LD path `Kbd` means the low-overlap window (FDK maps the LD
/// shape bit the same way); LD never uses a Kaiser window.
pub window_shape: WindowShape,
/// Number of coded scalefactor bands.
pub max_sfb: u8,
/// 1 for long, 8 for short.
pub num_windows: u8,
/// Groups implied by `scale_factor_grouping`.
pub num_window_groups: u8,
/// Windows per group (sums to `num_windows`).
pub window_group_length: [u8; 8],
/// Number of SWB in the table for this rate / sequence.
pub num_swb: u8,
/// ER AAC LD (AOT 23): long windows only. 512 or 480 lines.
pub ld: bool,
/// Core samples in this frame: 1024, 960, 512, or 480.
/// Zero means the profile default (1024, or 512 when `ld`).
pub frame_len: u16,
/// `predictor_data_present` (Main or LTP). Eight-short frames stay clear.
pub predictor_present: bool,
/// Main reset group, 0 when the frame did not ask for a reset.
pub pred_reset_group: u8,
/// Bit `sfb` set means Main prediction is added on that band.
pub pred_used: u64,
/// LTP payload follows `predictor_data_present` and its present flag.
pub ltp_present: bool,
/// LTP lag in samples (11 bits).
pub ltp_lag: u16,
/// Index into the 8-entry LTP coefficient table.
pub ltp_coef_idx: u8,
/// Bit `sfb` set means add the LTP estimate on that long-window band.
pub ltp_used: u64,
}
impl IcsInfo {
/// Parse Table 4.6. LC rejects predictor / LTP bodies.
pub fn parse(br: &mut BitReader<'_>, fs_index: u8, common_window: bool) -> Result<Self> {
Self::parse_mode(br, fs_index, common_window, super::asc::AOT_LC, 0)
}
/// `aot` selects LD windows and the Main / LTP predictor body.
/// `frame_len` is 960, 480, 512, or 1024; zero selects 512 for LD and
/// 1024 otherwise.
pub fn parse_mode(
br: &mut BitReader<'_>,
fs_index: u8,
common_window: bool,
aot: u8,
frame_len: u16,
) -> Result<Self> {
let ld = aot == super::asc::AOT_LD;
let _reserved = br.read_bit()?;
let window_sequence = WindowSequence::from_bits(br.read(2)? as u8);
let window_shape = WindowShape::from_bit(br.read_bit()?);
if ld && !matches!(window_sequence, WindowSequence::OnlyLong) {
// ER AAC LD carries long windows only (FDK: AAC_DEC_PARSE_ERROR).
return Err(Error::IcsInfoInvalid);
}
let mut predictor_present = false;
let mut pred_reset_group = 0u8;
let mut pred_used = 0u64;
let mut ltp_present = false;
let mut ltp_lag = 0u16;
let mut ltp_coef_idx = 0u8;
let mut ltp_used = 0u64;
let (max_sfb, grouping) = if window_sequence.is_eight_short() {
(br.read(4)? as u8, Some(br.read(7)? as u8))
} else {
let max_sfb = br.read(6)? as u8;
if br.read_bit()? {
if aot == super::asc::AOT_MAIN {
let (group, used) = super::pred::read_main(br, max_sfb, fs_index)?;
predictor_present = true;
pred_reset_group = group;
pred_used = used;
} else if aot == super::asc::AOT_LTP {
let (present, lag, coef, used) = super::ltp::read_present(br, max_sfb)?;
predictor_present = true;
ltp_present = present;
ltp_lag = lag;
ltp_coef_idx = coef;
ltp_used = used;
} else {
// AAC-LC shall not carry predictor / LTP (§1.5.1.1).
return Err(Error::Format("predictor/LTP on LC stream"));
}
}
let _ = common_window;
(max_sfb, None)
};
let (num_windows, num_window_groups, window_group_length) =
grouping_of(window_sequence, grouping);
let frame_len = resolve_frame_len(ld, frame_len);
let offsets = if window_sequence.is_eight_short() {
if frame_len == 960 {
super::swb::short_offsets_960(fs_index)?
} else {
short_offsets(fs_index)?
}
} else if ld {
if frame_len == 480 {
super::swb::long_offsets_ld480(fs_index)?
} else {
super::swb::long_offsets_ld(fs_index)?
}
} else if frame_len == 960 {
super::swb::long_offsets_960(fs_index)?
} else {
long_offsets(fs_index)?
};
let num_swb = offsets.len().saturating_sub(1) as u8;
if max_sfb as usize > num_swb as usize {
return Err(Error::IcsInfoInvalid);
}
Ok(IcsInfo {
window_sequence,
window_shape,
max_sfb,
num_windows,
num_window_groups,
window_group_length,
num_swb,
ld,
frame_len,
predictor_present,
pred_reset_group,
pred_used,
ltp_present,
ltp_lag,
ltp_coef_idx,
ltp_used,
})
}
/// Samples in one long window, or one of the eight short windows.
#[must_use]
pub fn window_len(&self) -> usize {
let core = self.core_len();
if self.window_sequence.is_eight_short() {
core / 8
} else {
core
}
}
/// PCM samples this frame contributes (1024, 960, 512, or 480).
#[must_use]
pub fn core_len(&self) -> usize {
match self.frame_len {
960 | 480 | 512 | 1024 => usize::from(self.frame_len),
_ => {
if self.ld {
super::swb::LD_WINDOW_LEN
} else {
super::swb::LONG_WINDOW_LEN
}
}
}
}
/// `swb_offset` table for this frame's sequence / profile.
pub fn swb_offsets(&self, fs_index: u8) -> Result<&'static [u16]> {
let frame_len = self.core_len();
if self.window_sequence.is_eight_short() {
if frame_len == 960 {
super::swb::short_offsets_960(fs_index)
} else {
short_offsets(fs_index)
}
} else if self.ld {
if frame_len == 480 {
super::swb::long_offsets_ld480(fs_index)
} else {
super::swb::long_offsets_ld(fs_index)
}
} else if frame_len == 960 {
super::swb::long_offsets_960(fs_index)
} else {
long_offsets(fs_index)
}
}
}
fn resolve_frame_len(ld: bool, frame_len: u16) -> u16 {
if ld {
if frame_len == 480 { 480 } else { 512 }
} else if frame_len == 960 {
960
} else {
1024
}
}
pub(crate) fn grouping_of(seq: WindowSequence, grouping: Option<u8>) -> (u8, u8, [u8; 8]) {
if !seq.is_eight_short() {
let mut lens = [0u8; 8];
lens[0] = 1;
return (1, 1, lens);
}
let gbits = grouping.unwrap_or(0);
let mut lens = [0u8; 8];
lens[0] = 1;
let mut groups = 1u8;
for i in 1..8 {
// bit 6 of the 7-bit field groups window 1 with window 0, …
if (gbits >> (6 - (i - 1))) & 1 == 1 {
lens[(groups - 1) as usize] += 1;
} else {
lens[groups as usize] = 1;
groups += 1;
}
}
(8, groups, lens)
}