v0.0.3

Other

• skip etsi_table_validation when docs sibling absent
• replace never-match regex with semver_check = false
• migrate to centralized OxideAV/.github reusable workflows
• round 28 — mono / stereo short-frame sf_data(ASF) walker
• round 27 — 7_X channel-element walker (immersive 7.0 / 7.1)
• round 26 — add per-codebook decode roundtrip sweeps
• round 25 — ASPX_ACPL_1 / ASPX_ACPL_2 inner body walker
• round 24 — grouped multichannel sf_data(ASF) walker + ASPX_ACPL_3 inner body walker
• round 23 — multichannel sf_data(ASF) Huffman codebook table walk
• round 22 — ASPX_ACPL_1/2 multichannel wrapper (Pseudocode 117) + 5_X-walker glue
• round 21 — ASPX_ACPL_3 transform synthesis (Pseudocodes 118/119)
• round 20 — ETSI Huffman table audit + 5.X cfg0/1/2 + sf_info_lfe
• round 19 — design 5_X channel-element walker family
• round 18 — wire ASPX_ACPL_1 joint-MDCT residual layer
• round 17 — wire A-CPL synthesis into Ac4Decoder
• adopt slim AudioFrame shape
• land §5.7.7 A-CPL QMF synthesis math (round-16)
• outer §4.2.14.1 metadata() walker + §5.7.7.2 sb_to_pb
• A.4 Huffman codebooks + dialog_enhancement parser
• A.3 Huffman codebooks + acpl_data_*ch parser
• A.5 Huffman codebook + drc_frame parser
• implement complex-covariance TNS (chirp + α0 + α1) — round-11
• land §5.7.6.4.2.2 A-SPX limiter (P72 + P96..101) — round-10
• pin release-plz to patch-only bumps

Added

• Round 28 — mono / stereo short-frame sf_data(ASF) walker (TS 103
  190-1 §4.2.8.3-6 Tables 39-42, §4.3.6.2.6 Pseudocodes 2/3/5):

  • New spec-correct _grouped payload parsers in asf_data.rs —
    parse_asf_section_data_grouped(),
    parse_asf_spectral_data_grouped(),
    parse_asf_scalefac_data_grouped(),
    parse_asf_snf_data_grouped() — each takes per-group transform-
    length and max_sfb arrays and walks the spec's outer
    for (g = 0; g < num_window_groups; g++) loop. Critically:
    asf_scalefac_data() consumes a single 8-bit
    reference_scale_factor at the head with first_scf_found shared
    across groups (DPCM state is continuous over the whole frame), and
    asf_snf_data() consumes a single 1-bit b_snf_data_exists
    gate at the head. This matches Tables 41 / 42 verbatim.
  • New helpers in asf.rs:
    derive_per_group() / derive_per_group_with_max_sfb() resolve
    per-group (transf_length_idx, transform_length, max_sfb) from
    (AsfTransformInfo, AsfPsyInfo) per Pseudocodes 2 (get_transf_length)
    and 5 (get_max_sfb), including the b_different_framing
    half-frame split (Pseudocode 3's grouping-bit shift +
    num_windows_0 - 1 boundary injection).
  • New body decoders:
    • decode_asf_grouped_mono_body[_with_max_sfb]() — wraps the four
      _grouped payload parsers; returns the per-group dequantised
      spectra concatenated group-major.
    • decode_asf_grouped_stereo_joint_body() — joint-MDCT residual
      layer with shared section, two independent spectral bodies (L/M
      then R/S), shared scalefactors (band-wise max_quant_idx over
      both channels), per-group ms_used[g][sfb] flag arrays, then
      snf. Inverse M/S applied per-group: L = M+S, R = M-S for bands
      with ms_used set.
    • decode_asf_mono_body_dispatch() /
      decode_asf_mono_body_for_max_sfb() — long-frame vs grouped
      dispatch wrappers used by all per-channel call sites.
  • Wired into the four mono / stereo call sites:
    • parse_mono_audio_data_outer() — mono SIMPLE / ASPX path.
    • parse_aspx_acpl2_mdct_body() — single-channel ASPX_ACPL_2
      MDCT residual.
    • parse_aspx_acpl1_mdct_body() joint + split — ASPX_ACPL_1
      joint-MDCT residual layer (two independent mono bodies with
      max_sfb_0 / max_sfb_side_0) and the split case.
    • parse_stereo_data_body() joint + split — stereo CPE body
      with both joint MDCT (shared section + ms_used) and split MDCT
      (two independent mono bodies).
  • Real Dolby AC-4 mono / stereo streams that include short-frame
    sf_data(ASF) (i.e. the encoder picks short-window sub-frames)
    now decode end-to-end without bailing at the
    num_window_groups != 1 guard. The grouped multichannel walker
    in mch.rs from r24 (per-group interleaved
    section + spectral + scalefac + snf) is left untouched — its
    pinned tests continue to pass.
  • 9 new tests: 4 in asf_data.rs (grouped section / scalefac
    reference-once / scalefac DPCM-state-carries / snf gate-once) and
    5 in asf.rs (decode_asf_grouped_mono two-group + truncated;
    parse_mono_audio_data_outer SIMPLE short-frame; parse_stereo_data_body
    split + joint short-frame). 425 tests (414 lib + 5 + 6
    integration), up from 416.

• Round 27 — 7_X channel-element walker (immersive 7.0 / 7.1)
  (TS 103 190-1 §4.2.6.14 Table 33 + §4.3.5.7 Table 98):

  • New parse_7x_audio_data_outer() walker in mch.rs plus a
    SevenXCodecMode enum (Table 98 — 2 bits, 4 codepoints: SIMPLE /
    ASPX / ASPX_ACPL_1 / ASPX_ACPL_2; no ASPX_ACPL_3 in 7.X). The
    walker mirrors the 5_X SIMPLE/ASPX path's coding_config selector
    but with the 7.X-specific shape:
    • 2-bit 7_X_codec_mode (vs 3-bit for 5_X — no Reserved values).
    • LFE mono_data(1) gated on channel_mode == "7.1" (mapped from
      the parent substream's channel count: 7 → 7.0, 8 → 7.1).
    • companding_control(5) for ASPX_ACPL_{1,2} only — SIMPLE/ASPX in
      7.X have no leading companding (different from 5_X where ASPX
      gets companding_control(5)).
    • Cfg0 body: 2ch_mode + two_channel_data + two_channel_data (no
      centre mono inside the switch).
    • Cfg2 body: four_channel_data only (no surround mono inside the
      switch). Both centre / surround monos move out to a single
      trailing mono_data(0) call gated on coding_config in {0, 2},
      placed after the additional-channel block.
    • SIMPLE/ASPX-only additional-channel block: 1-bit
      b_use_sap_add_ch gating optional chparam_info()×2, then a
      mandatory two_channel_data() for the front-extension /
      back-surround pair beyond the 5.X core. Lands in new
      tools.seven_x_b_use_sap_add_ch,
      tools.seven_x_add_chparam_info and
      tools.seven_x_additional_channel_data slots.
    • ASPX_ACPL_1-only joint-MDCT residual layer (max_sfb_master +
      chparam_info×2 + sf_data×2) — same shape as the 5_X path,
      n_side_bits derived per the Table 33 NOTE from the largest
      signalled transform length across all preceding
      two_channel_data / three_channel_data / four_channel_data /
      five_channel_data (including the additional-channel one when
      it's the largest).
    • Trailers: aspx_data_2ch×2 + aspx_data_1ch for any non-SIMPLE,
      plus an extra aspx_data_2ch for ASPX (covering the additional
      pair); acpl_data_1ch×2 for ASPX_ACPL_{1,2} landing in
      tools.acpl_data_1ch_pair[0/1] (shared with the 5_X
      §5.7.7.6.1 pair walker).
  • walk_ac4_substream now dispatches channels == 7 (7.0) and
    channels == 8 (7.1) into the new walker. Previously these
    channel counts fell through to the catch-all that just records
    channel_mode_channels and bails — real Dolby AC-4 streams using
    a 7_X_channel_element now parse end-to-end without hitting the
    catch-all.
  • Walker is try-and-bail with the same contract as the 5_X
    walker: any inner Huffman / parse miss surfaces Ok(()) to the
    caller, leaving already-populated tools.* slots intact. The
    deeper aspx_data / acpl_data trailers are gated on
    b_iframe && tools.aspx_config.is_some().
  • 11 new lib tests (394 → 405 total): SIMPLE Cfg3 (no SAP), 7.1
    SIMPLE LFE walk, SIMPLE Cfg0 (two pairs + trailing centre mono),
    SIMPLE Cfg2 (four-channel + back surround mono), SIMPLE Cfg1 (no
    trailer), SIMPLE with b_use_sap_add_ch == 1 (chparam pair
    populated), ASPX_ACPL_2 non-iframe Cfg1 (no additional-channel
    block), ASPX_ACPL_1 I-frame Cfg0 (residual layer + Cfg0 trailer),
    ASPX_ACPL_1 zero max_sfb_master bails silently, truncated
    SIMPLE five_channel_data bails silently, and
    SevenXCodecMode::from_u32 round-trip.

• Round 25 — ASPX_ACPL_1 / ASPX_ACPL_2 inner body walker
  (TS 103 190-1 §4.2.6.6 Table 25 + §5.7.7.6.1 Pseudocode 117):

  • New parse_aspx_acpl_1_2_inner_body() helper in mch.rs walks the
    bits past the existing companding_control(3) + 1-bit coding_config selector for the 5_X ASPX_ACPL_1 / ASPX_ACPL_2
    paths. The body shape (Table 25):
    two_channel_data() OR three_channel_data() →
    [ASPX_ACPL_1 only] max_sfb_master (n_side_bits) + chparam_info()×2 + sf_data(ASF)×2 joint-MDCT residual layer →
    [coding_config==0 only] mono_data(0) centre/surround trailer →
    aspx_data_2ch() + aspx_data_1ch() + acpl_data_1ch()×2.
    The two acpl_data_1ch payloads land in
    tools.acpl_data_1ch_pair[0] (D0-side) and
    tools.acpl_data_1ch_pair[1] (D1-side) per Pseudocode 117 — the
    same pair the §5.7.7.6.1 run_acpl_5x_pair_pcm() PCM driver
    consumes.
  • n_side_bits is derived per the §4.2.6.6 NOTE: largest signalled
    transform length from the preceding two_channel_data() /
    three_channel_data() (look up tables::n_msfb_bits_48 Table 106
    column 2). The joint-MDCT residual sf_data bodies reuse
    decode_asf_long_mono_body_with_max_sfb() against a synthesised
    long-frame AsfTransformInfo at the dominant transform length.
  • The walker is try-and-bail: every step returns Ok(()) to the
    outer walker on any inner Huffman / parse miss, leaving the
    already-populated tools.* slots intact (matching the round-24
    ASPX_ACPL_3 walker contract). Deeper aspx_data / acpl_data steps
    are gated on b_iframe && tools.aspx_config.is_some() —
    non-iframe paths simply consume what they can of the upstream
    channel data and stop.
  • Active acpl_config_1ch for the pair-extraction step is selected
    by codec mode: acpl_config_1ch_partial for ASPX_ACPL_1 (with
    start_band derived from qmf_band via acpl::sb_to_pb()),
    acpl_config_1ch_full for ASPX_ACPL_2 (start_band always 0).
  • 6 new lib tests + 2 new tests/acpl_5x_pipeline.rs integration
    tests (387 → 395 total): non-iframe ASPX_ACPL_2 coding_config==0
    path lands two_channel_data + cfg0_centre_mono and leaves the
    ACPL pair None (gated); non-iframe ASPX_ACPL_1
    coding_config==1 path lands three_channel_data and walks the
    joint-MDCT residual layer; I-frame ASPX_ACPL_2 with
    three_channel_data parses aspx_config + acpl_config_1ch_full
    out of the bitstream and walks the channel data; I-frame
    ASPX_ACPL_1 with Cfg0 walks the residual layer + Cfg0 mono trailer
    end-to-end; truncated three_channel_data mid-bitstream bails
    silently with Ok(()); max_sfb_master == 0 in the residual
    layer bails silently. Two integration tests assert the
    walker → synthesis glue: a real Table-27 three_channel_data()
    body now flows into tools.three_channel_data (which the r22
    walker treated as opaque), and the staged ACPL pair drives
    run_acpl_5x_pair_pcm() end-to-end for both ASPX_ACPL_1 and
    ASPX_ACPL_2 modes.

• Round 24 — Grouped multichannel sf_data(ASF) walker + ASPX_ACPL_3
  inner body walker (TS 103 190-1 §4.2.6.6 + §5.4.4.4 + Table 52 / 62):

  • decode_mch_sf_data_channels() in mch.rs now also handles the
    grouped / short-frame case (num_window_groups > 1). A new
    decode_asf_grouped_mono_body_with_max_sfb() helper walks
    num_window_groups independent (asf_section_data + asf_spectral_data + asf_scalefac_data + asf_snf_data) chains per
    body and concatenates the per-group dequantised spectra
    group-major into a single Vec<f32> of length
    num_window_groups * sfb_offset[max_sfb]. With b_dual_maxsfb = 0
    every group shares the same max_sfb_0, matching Pseudocode 5
    get_max_sfb(g) for the non-side-channel multichannel path.
    parse_two_channel_data / parse_three_channel_data /
    parse_four_channel_data / parse_five_channel_data now populate
    scaled_spec_per_channel for both the long-frame /
    single-window-group (r23) and the grouped / multi-window-group
    paths.
  • parse_5x_audio_data_outer for 5_X_codec_mode == ASPX_ACPL_3
    now walks the inner body (Table 25 row ASPX_ACPL_3:
    stereo_data() + aspx_data_2ch() + acpl_data_2ch()). The flow is:
    parse_stereo_data_body() → on success + I-frame +
    tools.aspx_config.is_some(), parse_aspx_data_2ch_body() →
    parse_acpl_data_2ch(num_param_bands, 0, qm0, qm1). The parsed
    tools.acpl_data_2ch slot now flows straight into the
    §5.7.7.6.2 Pseudocode-118 5_X synthesis pipeline (closing the
    contract the round-22 staging tests stubbed by hand).
  • Refactor: factored the Table-52 aspx_data_2ch() body parser
    out of the stereo CPE ASPX path (parse_stereo_audio_data_outer)
    into a shared pub(crate) parse_aspx_data_2ch_body() helper in
    asf.rs. Both the stereo CPE StereoCodecMode::Aspx mode and
    the new 5_X ASPX_ACPL_3 mode now drive this single parser —
    one definition of aspx_xover_subband_offset + aspx_framing(0) + aspx_balance + [aspx_framing(1)] + aspx_delta_dir(0/1) + aspx_hfgen_iwc_2ch + 4x aspx_ec_data instead of two divergent
    inline copies.
  • 7 new tests (380 → 387 total): grouped two-group two-channel walk
    with all-zero spectra (length matches 2 * sfb_offset[max_sfb]);
    three-group one-channel walk pinning the linear num_window_groups
    scale; parse_three_channel_data grouped-short-frame end-to-end
    walk through parse_5x_audio_data_outer; parse_two_channel_data
    grouped-short-frame walk for Cfg0 / Cfg1; truncated grouped input
    yields None without panicking; ASPX_ACPL_3 non-iframe leaves
    tools.acpl_data_2ch == None; ASPX_ACPL_3 I-frame parses the
    aspx_config + acpl_config_2ch configs out of the bitstream and
    surfaces them on tools (the inner body walker bails silently
    downstream of stereo_data() on a degenerate aspx_config — that
    bail is part of the try-and-bail contract).

• Round 23 — Multichannel sf_data(ASF) Huffman codebook table walk
  (TS 103 190-1 §4.2.6.7-10 Tables 26 / 27 / 28 / 29):

  • New decode_mch_sf_data_channels() helper in mch.rs walks
    n_channels consecutive sf_data(ASF) bodies sharing the head
    (transform_info, psy_info) pair. Each body decodes
    asf_section_data then asf_spectral_data then asf_scalefac_data
    then asf_snf_data per §4.2.8.3-6, producing one dequantised + scaled
    MDCT spectrum per channel of length sfb_offset[max_sfb].
  • parse_two_channel_data() / parse_three_channel_data() /
    parse_four_channel_data() / parse_five_channel_data() now walk
    the trailing 2 / 3 / 4 / 5 sf_data(ASF) calls and store the
    per-channel scaled spectra on each *ChannelData::scaled_spec_per_channel
    (new Vec<Option<Vec<f32>>> field). For the long-frame,
    single-window-group case every slot is populated; short / grouped
    frames push Some(...) for none of the slots and let the outer
    shell still parse cleanly.
  • Huffman codebook IDs wired (per Annex A.1, all reused from the
    mono / stereo paths — there is no separate "MCH" codebook set):
    HCB_1 (ASF_HCB_1_LEN/CW, 81 entries) through HCB_11
    (ASF_HCB_11_LEN/CW, 289 entries) for spectral lines,
    HCB_SCALEFAC (ASF_HCB_SCALEFAC_LEN/CW, 121 entries) for
    scale-factor DPCM, and HCB_SNF (ASF_HCB_SNF_LEN/CW, 22 entries)
    for spectral noise fill. Round 22's
    decode_asf_long_mono_body_with_max_sfb was raised from fn to
    pub(crate) fn so mch.rs can drive one body per channel from the
    shared sf_info block.
  • Removed the previous "scaffold values" comments / TODOs from
    mch.rs for the per-channel sf_data(ASF) paths — the per-channel
    spectra now flow through the validated ASF Huffman codebook suite
    (audited byte-for-byte in r20's etsi_table_validation.rs against
    docs/audio/ac4/ts_10319001v010401p0-tables.c).
  • 6 new tests (374 → 380 total): all-zero two-channel sf_data round
    trip with sfb-offset length pin, short-frame guard returns all-None,
    parse_three_channel_data decodes 3 bodies with all-zero spectra
    pin, parse_four_channel_data + parse_five_channel_data
    per-channel-count pin, truncated sf_data graceful partial decode,
    parse_two_channel_data per-channel length-matches-sfb-offset pin.
    The pre-existing 5_X outer-walker tests (parse_5x_outer_simple_*)
    were extended to feed valid all-zero sf_data(ASF) trailers so they
    still exercise the outer dispatch end-to-end.

• Round 22 — ASPX_ACPL_1/2 multichannel wrapper (Pseudocode 117) +
  5_X-walker glue:

  • New §5.7.7.6.1 multichannel pipeline in acpl_synth.rs:
    run_pseudocode_117_5x() wraps two parallel
    run_pseudocode_115_pair() passes (D0 decorrelator on the L-side
    ACplModule, D1 on the R-side) and forms the five 5.X output
    channels from the L/R/C carriers (plus optional Ls/Rs carriers in
    ASPX_ACPL_1 mode). Centre channel is a passthrough (z4 = x2);
    surround pair (z1/z3) gets the spec's final sqrt(2) scale.
  • New Acpl5xPairState (left/right AcplCpeState + alpha/beta
    differential-decode rolling state for two acpl_data_1ch rows),
    Acpl5xPairFrame (5 carrier slots + two (alpha_dq, beta_dq)
    matrices + interpolation control), Acpl5xPairMode selector
    (AspxAcpl1 vs AspxAcpl2), and Acpl5xPairOutput (z0/z1/z2/z3/z4).
  • PCM-level helpers wire the parsed 5_X bitstream straight through
    QMF analysis → A-CPL → QMF synthesis:
    • run_acpl_5x_pair_pcm() — drives Pseudocode 117 from
      (pcm_l, pcm_r, pcm_c[, pcm_ls, pcm_rs], cfg, data_1, data_2).
    • run_acpl_5x_mch_pcm() — drives Pseudocode 118 from
      (pcm_l, pcm_r, pcm_c, acpl_config_2ch, acpl_data_2ch).
      Both return Acpl5xPcmOutput { left, right, centre, left_surround, right_surround } PCM buffers and bundle the QMF banks + ACPL state
      in Acpl5xPairPcmState / Acpl5xMchPcmState.
  • New SubstreamTools fields: acpl_data_2ch (parsed
    acpl_data_2ch() per Table 62, for ASPX_ACPL_3) and
    acpl_data_1ch_pair: [Option<...>; 2] (one acpl_data_1ch() per
    parallel ACplModule, for the 5_X ASPX_ACPL_1/2 paths).
  • 8 new lib tests + 3 new tests/acpl_5x_pipeline.rs integration
    tests (363 → 374 total): D0/D1 decorrelator-id init,
    Pseudocode 117 ASPX_ACPL_2 centre passthrough + finite-output,
    ASPX_ACPL_1 low-band M/S split spot-check, prev-state carry across
    frames, ASPX_ACPL_2 equivalence to two parallel
    run_pseudocode_115_pair() passes, PCM-level input rejection
    (misaligned / surround-presence vs. mode), end-to-end 5-channel
    PCM emission for both ASPX_ACPL_2 and ASPX_ACPL_3, and the
    walker-→-synthesis glue for all three multichannel modes (the
    walker hands back acpl_config_* slots, the test stages
    acpl_data_* and asserts the synthesis pipeline consumes the
    pair without further glue).

• Round 21 — ASPX_ACPL_3 transform synthesis (Pseudocodes 118/119):

  • New §5.7.7.6.2 multichannel pipeline in acpl_synth.rs:
    transform() (Pseudocode 119) linearly mixes the two A-CPL
    carriers (x0, x1) by interpolated gamma matrices g1, g2;
    acpl_module2() (Pseudocode 119) builds the (z0, z1) channel
    pair from g1+g1*a, g2+g2*a and the beta-weighted decorrelator
    output; acpl_module3() (Pseudocode 119) adds the beta3-driven
    cross-residual term 0.25*y2*(b3 ± b3*a) to an existing pair.
  • New run_pseudocode_118_5x() runs the full 5-channel synthesis
    end-to-end: x0/x1 input scaling by (1 + 2*sqrt(0.5)), three
    parallel Transform() outputs into the D0/D1/D2 decorrelators
    • transient duckers (one persistent state per path), three
      ACplModule2() channel-pair builds (L/Ls, R/Rs, C with a=1, b=0),
      three ACplModule3() cross-residual corrections, and the final
      sqrt(2) channel scaling for z1, z3, z4.
  • New AcplMchState (D0/D1/D2 + 3x ducker + per-pset prev gammas),
    AcplMchFrame (5 input channels + 6 gammas + 5 alpha/beta arrays
    • interpolation control), AcplMchOutput (z0/z1/z2/z3/z4) and
      AcplQmfMatrix type alias.
  • 11 new lib tests (352 → 363 total): unit-gamma Transform(),
    mixed-gamma combinator, ACplModule2 zero-coupling, half-x0
    passthrough, ACplModule3 residual + no-op cases, full
    run_pseudocode_118_5x() 5-channel smoke test (finite + non-zero
    on all five outputs), zero-alpha-beta degenerate path, pb_matrix_*
    helpers, scaling-factor invariant 1 + 2*sqrt(0.5) == 1 + sqrt(2),
    AcplMchState::new() zero-init.

• Round 20 — ETSI Huffman table audit + 5.X coding-config wiring:

  • New tests/etsi_table_validation.rs integration suite parses the
    canonical ETSI accompaniment file
    docs/audio/ac4/ts_10319001v010401p0-tables.c at runtime via a tiny
    C-array tokeniser and validates every Huffman codebook this crate
    ships (huffman_tables.rs ASF, aspx_huffman.rs A-SPX,
    acpl_huffman.rs A-CPL, de_huffman.rs DE, drc_huffman.rs DRC)
    byte-for-byte against it. 60 codebooks, 120 arrays, 0 divergences
    found.
  • mch::parse_two_channel_data() lands the Table 26 outer shell
    (sf_info + chparam_info). The 5.X walker now wires Cfg0
    (2ch_mode + two_channel_data ×2 + mono_data(0)), Cfg1
    (three_channel_data + two_channel_data) and Cfg2 (four_channel_data
    • mono_data(0)) — previously gated as r20 TODO behind round-19's
      Cfg3-only path. New SubstreamTools fields: b_2ch_mode,
      two_channel_data: Vec<TwoChannelData>, cfg0_centre_mono,
      cfg2_back_mono.
  • asf::parse_asf_psy_info_lfe() splits the LFE sf_info_lfe()
    parser from the regular parse_asf_psy_info(). Table 106 column 4
    n_msfbl_bits (3 bits @ 1920, 2 bits @ 512, etc.) is now used for
    max_sfb[0] instead of the regular n_msfb_bits, and
    parse_mono_data(b_lfe=true) dispatches to it. The function
    rejects transform lengths whose n_msfbl_bits == 0 (Table 21
    permits long-frame transforms only on LFE).
  • 5 new lib tests + 6 new integration tests (337 → 352 total).

• A-CPL decoder wiring (round 17): ASPX_ACPL_2 substreams now go
  through the §5.7.7 channel-pair synthesis end-to-end. The asf walker
  parses aspx_data_1ch() (Table 51) and acpl_data_1ch() (Table 61)
  for the ASPX_ACPL_2 path; Ac4Decoder runs acpl_synth::run_acpl_1ch_pcm
  (mono PCM → QMF analysis → §5.7.7.5 channel-pair → QMF synthesis × 2)
  to emit a real stereo signal in place of the duplicate-of-primary
  fallback. ASPX_ACPL_1's joint-MDCT body is still gated.