Changelog

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0.6.1 - 2026-06-11

Changed

  • Rustler 0.38.0 is now used for source builds, and the rustler_precompiled requirement now targets 0.9.0. This keeps the NIF packaging stack current; the public Elixir API is unchanged.
  • Development-only Hex dependencies and compatible Rust lockfile dependencies were refreshed to their latest patch releases.

0.6.0 - 2026-06-10

Fixes every finding from the 2026-06 multi-agent Rust/STT NIF audit (label stt-rust-audit): silent text loss, faster-whisper parity gaps in the mel preprocessor and word alignment, and late or raising error paths. Word timings now track the faster-whisper reference within one encoder frame (20 ms).

Changed

  • ct2rs 0.9.18 → 0.9.19, bumping the vendored CTranslate2 from 4.7.1 to 4.7.2. (#34)
  • The daily security workflow audits the NIF crate's Rust dependency tree with cargo-audit, alongside the existing mix deps.audit. (#34)

Fixed

  • Word text from :word_timestamps is decoded through the tokenizer's byte-level BPE decoder. Non-ASCII words used to come back as mojibake ("schön" surfaced as "schön"), and codepoints split across tokens glued into one giant word; both now match faster-whisper, including per-codepoint word splitting for spaceless languages (zh, ja, th, lo, my, yue). (#19)
  • The last word of every 30 s chunk ends at the alignment's EOT boundary instead of a fabricated 20 ms duration. (#23)
  • Fallback segment ends (unclosed timestamp pair, or with_timestamps: false) are bounded by the chunk's real audio length; a 3 s clip no longer reports a segment ending at 30 s. (#24)
  • PCM containing NaN or infinity is rejected as :invalid_request instead of silently transcribing the corrupted region as silence. Amplitudes that overflow the mel power are rejected the same way. (#20)
  • The 2 GiB mel-buffer cap is enforced from input sizes before the PCM copy and the mel chunks are allocated, not after. (#21)
  • WhisperCt2.available_devices/0 runs on a dirty scheduler. On CUDA builds its first call initialises the NVIDIA driver, which used to stall a normal BEAM scheduler for the whole driver init. (#22)
  • WhisperCt2.load_model/2 fails at load when the tokenizer lacks <|startofprev|>, instead of degrading at inference time once :initial_prompt is used. (#31)
  • The word-timestamp alignment prompt no longer carries an explicit <|notimestamps|> — CTranslate2 appends it internally, so the decoder used to see the token doubled, perturbing the cross-attention word timings derive from relative to faster-whisper. (#25)
  • Text generated without an opening timestamp — a :prefix echo, a fine-tune opening with text, or text between lone timestamps — is kept as its own segment instead of silently discarded. (#26)
  • Log-mel normalisation floors against the whole audio's maximum, as faster-whisper does, instead of per 30 s window; a near-silent window of a longer audio is no longer normalised against its own max. (#27)
  • Reflect padding for audio shorter than 200 samples reads the zero-padded region like the reference instead of duplicating the last sample into the entire leading pad. (#28)
  • WhisperCt2.load_model/2 validates preprocessor_config.json: a zero numeric field or a mis-shaped mel_filters matrix fails as :load_error naming the offending field, instead of an opaque :nif_panic at the first transcribe. (#29)
  • Integer options that overflow the NIF's fixed-width types (u32 / i32) are rejected as :invalid_request instead of raising ArgumentError at the NIF boundary. (#30)

0.5.0 - 2026-05-20

Initial public release. Native Elixir Whisper speech-to-text backed by CTranslate2 through a Rustler NIF over ct2rs::sys::Whisper. No Python.

Features

  • WhisperCt2.load_model/2 loads a CTranslate2-converted Whisper model directory and returns a %WhisperCt2.Model{} with resolved :device and :compute_type.
  • WhisperCt2.transcribe/3 accepts {:pcm_f32, binary} (mono, 16 kHz, little-endian f32) and returns a %WhisperCt2.Transcription{} whose :segments carry absolute start/end times, :no_speech_prob, :avg_logprob, the underlying token IDs, and optional per-word timing.
  • WhisperCt2.transcribe_batch/3 stacks every chunk of every input into one encoder forward pass - a large speedup for diarization-driven workflows with many short turns.
  • :initial_prompt and :prefix bias decoding; :word_timestamps adds a batched DTW alignment pass attaching %WhisperCt2.Word{} entries; :with_timestamps toggles <|t_..|> segment timestamps for plain-text fine-tunes.
  • English-only checkpoints (*.en) use the [<|startoftranscript|>] prompt; multilingual checkpoints use [sot, lang, transcribe].
  • WhisperCt2.Pcm.slice/4 carves sub-windows out of an already-decoded f32 buffer with loud bounds checking.
  • WhisperCt2.available_devices/0 reports CPU/CUDA device counts and the build's CUDA-support flag.
  • Structured %WhisperCt2.Error{} taxonomy: :invalid_request, :load_error, :inference_error, :runtime_error, :nif_panic, :native_error.

Backends

  • Precompiled NIF artefacts via rustler_precompiled for aarch64-apple-darwin (Accelerate), x86_64-unknown-linux-gnu (oneDNN, optional mkl variant), and aarch64-unknown-linux-gnu (oneDNN). CUDA is loaded lazily via cuda-dynamic on every Linux artefact, so one binary runs on CPU-only and CUDA hosts alike.
  • Opt into a source build with WHISPER_CT2_BUILD=1, or pick the MKL artefact on x86_64 Linux with WHISPER_CT2_VARIANT=mkl.