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Whisper large-v2

OpenAI's openai/whisper-large-v2 ported to transcribe.cpp. A 1.55B-parameter encoder-decoder transformer (audio encoder + autoregressive text decoder with cross-attention).

What it's for

Offline multilingual speech-to-text and any-language → English speech translation. The model auto-detects the audio's language (99 languages covered) and emits a transcript in that language; passing language="<code>" and task="translate" to the underlying whisper_full_params produces an English translation instead. transcribe-cli reads a 16 kHz mono WAV and returns the transcript text. Long audio is handled via 30-second chunked decoding.

See the upstream model card for training data, intended use, and the original evaluation methodology.

Licensed Apache-2.0. Ported from upstream commit ae46427, pinned 2026-04-25. Validated against the transformers reference at transcribe.cpp commit 5.6.1 on 2026-04-26.

Download

Quantization Download Size WER (LibriSpeech test-clean)
F32 whisper-large-v2-F32.gguf 5.75 GB 2.68%
F16 whisper-large-v2-F16.gguf 2.89 GB 2.94%
Q8_0 whisper-large-v2-Q8_0.gguf 1.55 GB 2.65%
Q6_K whisper-large-v2-Q6_K.gguf 1.21 GB 2.83%
Q5_K_M whisper-large-v2-Q5_K_M.gguf 1.08 GB 2.72%
Q4_K_M whisper-large-v2-Q4_K_M.gguf 950 MB 2.46%

WER measured on the full LibriSpeech test-clean split (2620 utterances) with transcribe.cpp's default greedy decode and segment timestamps enabled — the same runs summarized in the Whisper family table. Numbers come from a single Metal-backed run; Metal's non-deterministic parallel reductions add ~0.1pp of run-to-run variance on the noise floor, and quantization is otherwise generally WER-neutral. See the WER methodology for the harness.

Quick Start

cmake -B build
cmake --build build

build/bin/transcribe-cli \
  -m models/whisper-large-v2/whisper-large-v2-Q8_0.gguf \
  samples/jfk.wav

If your audio is not already 16 kHz mono WAV, convert it first:

ffmpeg -i input.mp3 -ar 16000 -ac 1 output.wav

Performance

Cells are wall-clock latency (mel + encode + decode, mean over the recorded iterations after warmup), with speedup over realtime in parentheses. Units: ms below 1 s, s above (2 decimal places). Decode latency dominates as model size grows; the encoder is only run once per 30-second window.

Apple M4 Max

Backend Sample Q8_0 Q4_K_M
Metal jfk (11.0s) 508.0 ms (21.7×) 498.3 ms (22.1×)
Metal dots (35.3s) 1.37 s (25.7×) 1.33 s (26.5×)
CPU jfk (11.0s) 9.66 s (1.1×) 7.46 s (1.5×)
CPU dots (35.3s) 19.72 s (1.8×) 15.43 s (2.3×)

macOS 26.4.1, transcribe.cpp e0fa0f6.

Benchmark reproduction:

uv run scripts/bench/run.py \
  --models whisper-large-v2 \
  --quants q8_0,q4_k_m \
  --samples jfk,dots \
  --backends metal,cpu \
  --iters 3 --warmup 1 \
  --name whisper-large-v2-publication

AMD Ryzen 7 PRO 4750U

Backend Sample Q8_0 Q4_K_M
Vulkan jfk (11.0s) 6.27 s (1.8×) 6.07 s (1.8×)
Vulkan dots (35.3s) 14.29 s (2.5×) 13.68 s (2.6×)
CPU jfk (11.0s) 25.73 s (0.4×) 19.46 s (0.6×)
CPU dots (35.3s) 53.75 s (0.7×) 43.11 s (0.8×)

Fedora 43, transcribe.cpp e0fa0f6. Vulkan device: AMD Radeon Graphics (RADV RENOIR).

Benchmark reproduction:

uv run scripts/bench/run.py \
  --models whisper-large-v2 \
  --quants q8_0,q4_k_m \
  --samples jfk,dots \
  --backends cpu,vulkan \
  --iters 3 --warmup 1 \
  --name whisper-large-v2-publication

Numerical Validation

transcribe.cpp is validated tensor-by-tensor against the transformers reference (WhisperForConditionalGeneration, fp32 CPU) on the manifest's case (samples/jfk.wav). All 23 checkpointed tensors fall within per-variant tolerance, and the transcript matches the HF reference verbatim. Tolerance budget lives at tests/tolerances/whisper-large-v2.json. Last validated at commit 1854f57.

Field Value
Reference transformers 5.6.1 (WhisperForConditionalGeneration, CPU fp32)
Manifest tests/golden/whisper/whisper-large-v2.manifest.json
Tolerance file tests/tolerances/whisper-large-v2.json
Command uv run scripts/validate.py all --family whisper --variant whisper-large-v2

Selected tensors (worst observed across cases; see tolerance file for per-tensor budgets):

Tensor Max abs diff Mean abs diff Notes
enc.mel.in 2.229e-05 3.381e-08 fp32 mixed-radix FFT vs torch fp64 frontend
enc.conv1.out 3.725e-06 2.701e-08 fp32 conv stem
enc.conv2.out 1.800e-05 4.611e-07 stride-2 conv stem (matches enc.embed.out)
enc.block.0.out 5.424e-05 1.111e-06 first encoder block
enc.block.31.out 1.822e-02 3.259e-06 final encoder block (peak signal grows with depth)
enc.final 1.213e-03 2.945e-06 post-LN encoder output
dec.token_emb 0.000e+00 0.000e+00 exact zero-drift (ggml_get_rows on the F32 GGUF)
dec.block.0.out 4.530e-06 2.545e-07 first decoder block, prompt pass
dec.block.31.out 6.104e-05 1.777e-06 final decoder block (accumulated)
dec.out_before_head 4.387e-05 2.792e-06 post final LN, pre-vocab projection
dec.logits_raw 3.910e-05 9.921e-06 vocab projection (raw logits)
dec.logits 7.486e-05 1.652e-05 log-softmax over vocab
dec.logits_raw.gen20 9.537e-06 2.033e-06 step-20 logits (KV-cached path)

The C++ mel frontend (Slaney filterbank + Hann periodic window + whisper-style log-mel compression) drives enc.mel.in to fp32-vs-fp64 STFT precision drift; downstream tensors stay within budget. KV-cached decoder runs through F16 self/cross caches by default — flip with --kv-type f32 for tighter parity.

Reproduction

Convert

The whisper converter loads from a Hugging Face checkpoint and emits a reference-dtype GGUF.

uv run --project scripts/envs/whisper \
  scripts/convert-whisper.py openai/whisper-large-v2 \
  --revision ae46427

Quantize

Run transcribe-quantize once per target quant. Example for Q8_0; repeat for the other shipped presets:

build/bin/transcribe-quantize \
  models/whisper-large-v2/whisper-large-v2-F32.gguf \
  models/whisper-large-v2/whisper-large-v2-Q8_0.gguf \
  --quant Q8_0

Validate

uv run scripts/validate.py all --family whisper --variant whisper-large-v2

Run real-model tests

cmake -B build -DTRANSCRIBE_BUILD_REAL_MODEL_TESTS=ON
cmake --build build

TRANSCRIBE_WHISPER_GGUF=$PWD/models/whisper-large-v2/whisper-large-v2-Q8_0.gguf \
  ctest --test-dir build --output-on-failure -R whisper