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Brandon ThomasandClaude Opus 5.5
b936ed0055
New L0 crate effectcraft-opusenc: clean-room RFC 6716 CELT-only encoder (fullband 48 kHz, 20 ms packets, mono/stereo as dual L/R stereo, constant packet size from the bitrate) with the RFC 7845 OpusHead and pre-skip. Forward low-overlap MDCT, inter/intra coarse energy, fine/final energy, the decoder's exact allocation, recursive band splitting, PVQ search and codeword indexing, silence frames. crates/export depends on it; filmcraft-opus (dev) is the round-trip oracle in tests/opus_roundtrip.rs, with ffmpeg reading an in-test Ogg Opus file as a second oracle when installed. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
34 lines
1.8 KiB
Markdown
34 lines
1.8 KiB
Markdown
# effectcraft-opusenc
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Clean-room, pure-Rust Opus encoder for EffectCraft's WebM export audio (layer L0, `std` only,
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no `unsafe`).
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- **CELT-only** packets (TOC configuration 31: fullband 20 kHz, 20 ms, one frame per packet),
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48 kHz input, mono or stereo (stereo coded as dual L/R stereo), constant packet size from the
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requested bitrate; all-zero frames become 3-byte silence packets.
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- Forward MDCT with the low-overlap window, band energies with inter/intra coarse prediction
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(cheaper of the two per frame), fine and final energy bits, the decoder's exact bit allocation,
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spreading and recursive band splitting, greedy PVQ search and codeword indexing.
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- Not implemented: SILK/hybrid modes, transient (short-block) frames, TF changes, pitch
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post-filter, intensity stereo, dynamic allocation boosts, VBR rate control.
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- `OpusEncoder::pre_skip()` is 120 samples (the MDCT overlap); `opus_head()` returns the RFC 7845
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identification header.
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```rust
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let mut enc = effectcraft_opusenc::OpusEncoder::new(2, 128_000);
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let packet = enc.encode_float(&vec![0.0; effectcraft_opusenc::OpusEncoder::FRAME_SIZE * 2]);
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```
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## Specifications
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- RFC 6716, *Definition of the Opus Audio Codec* (September 2012), with the RFC 8251 updates
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(October 2017) as implemented by the decoder we round-trip against.
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- RFC 7845, *Ogg Encapsulation for the Opus Audio Codec* (April 2016), §5.1 `OpusHead` and
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§4.2 pre-skip.
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Implemented from the RFC text. Constant tables (band edges, `eMeans`, the coarse-energy Laplace
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model, the allocation table, ICDFs) and the decoder-side allocation arithmetic are mirrored from
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FilmCraft's first-party, spec-derived `filmcraft-opus` decoder (MIT OR Apache-2.0), which is also
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the round-trip oracle in `crates/export/tests/opus_roundtrip.rs` (ffmpeg is a second, external
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oracle when installed). No third-party encoder or decoder source was consulted.
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