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OWSM-CTC
OWSM-CTC is ESPnet's non-autoregressive multilingual speech recognition and speech translation family. The v4 checkpoint is espnet/owsm_ctc_v4_1B. It uses an E-Branchformer encoder with self-conditioned CTC and is separate from the autoregressive OWSM family.
Usage
audiocpp_cli --task asr --family owsm_ctc \
--model /path/to/OWSM-CTC-GGUF/owsm-ctc-v4-1b-f32.gguf \
--backend cuda --audio input.wav \
--request-option language=eng --text-out transcript.txt --log
Add --request-option target_language=deu to translate into German instead
of transcribing. Language values are the checkpoint's ISO 639-3 codes, such as
eng, jpn, and zho. language=auto uses unknown-language conditioning;
it does not report a detected language.
The model runs offline best-path CTC decoding. It does not generate timestamp tokens, use an autoregressive beam, or condition on previous transcript text.
Common Options
| CLI option | Description |
|---|---|
--audio |
Input audio; resampled to mono 16 kHz. |
--backend |
Execution backend. |
--mode |
offline (default) or streaming text output from a complete audio file. |
--threads |
CPU thread count. |
--text-out |
Transcript output path. |
Request Options (Use With --request-option)
| Option | Default | Description |
|---|---|---|
language |
eng |
Input language code; auto uses unknown-language conditioning. |
target_language |
Unset | Translation target language; omit for transcription. |
audio_chunk_mode |
auto |
auto, fixed, or none. |
Session Options (Use With --session-option)
| Option | Default | Description |
|---|---|---|
owsm_ctc.weight_type |
native |
Matmul weight storage override. |
Long Audio
auto pads short input to the trained 30-second window. Longer recordings use
overlapping 30-second windows with two seconds of context on each side.
CTC frame predictions are joined before collapsing repeated tokens and blanks.
fixed also applies this overlapping-window path to short audio. none rejects
input longer than 30 seconds. The result is a whole-recording transcript,
without word or segment timestamps.
Streaming
Add --mode streaming for incremental text output from a complete audio file.
Each completed long-form window emits only newly committed text. CTC repeat
and blank collapsing continues across window boundaries. Short input produces
one text update after its window completes. The final transcript is identical
to offline mode with the same settings. This is not live microphone streaming.
For the server, configure the model with "mode": "streaming" and send:
curl http://localhost:8080/v1/audio/transcriptions \
-F model=owsm_ctc -F file=@input.wav -F language=eng -F stream=true
The response uses transcript.text.delta followed by transcript.text.done.
Conversion
python tests/owsm_ctc/convert_gguf.py /path/to/owsm_ctc_v4_1B \
/path/to/OWSM-CTC-GGUF/owsm-ctc-v4-1b-f32.gguf \
--staging-dir /path/to/staging --type orig
Use --type q8_0 and a corresponding output filename for Q8. The GGUF includes
the tokenizer, configuration, normalization statistics, and model spec.