At high transcoding speed, high input-fidelity statements are not transcoded

[resolutecake]

Q1. When whisper.cpp transcodes a 5-hour audio file finding mostly noise, it enters a fast mode transcoding at 90×.
BUG: In this mode 1–3-minute conversations are missed, and leave no trace in the output

>>> How can I avoid whisper missing short conversations?

For example, should the context be periodically destroyed

Q2. When audio is 30h+ the file size exceeds 4 GiB which 32-bit .wav cannot handle producing empty files.

>>> How can I transcode large audio files or infinite streams?

ffmpeg has -rf64 option for RF64 format https://en.wikipedia.org/wiki/RF64
is there better input format than wav?
I would prefer feeding RAW samples, float or specific PCM

Q3. >>> Is there some other way of improving transcoding word-yield considering the below commands?

hardware is 8 GiB RAM 2021 Apple M processors macOS and 2 parallel whisper instances
A custom Go binding is being considered
It is batch execution, so slow transcode is not a problem

Creating the audio stream:

ffmpeg -hide_banner -i i.mp4 -nostdin -vn -ac 1 -ar 16000 -f wav -

whisper command:

./whisper.cpp/build/bin/main --model whisper.cpp/models/ggml-small.en.bin
--file - --output-lrc --output-file o.lrc

[resolutecake]

Anybody agrees with this below?

.

Action 1: use Go package
github.com/ggerganov/whisper.cpp/bindings/go/pkg/whisper

sample Go main function:
https://github.com/ggerganov/whisper.cpp/blob/ece3ff88f66cdc867d334ff4b8e8c00d9ffcebf7/bindings/go/examples/go-whisper/main.go

Go bindings provides access to method:
SetTokenThreshold
https://github.com/ggerganov/whisper.cpp/blob/ece3ff88f66c/bindings/go/params.go#L94

• it is unclear if the Whisper’s voice activity detector can be at all controlled
• possibly by lowering this value, more speech results and short conversations may not be missed
• it is possible this won’t work, whisper proper has a plethora of questionable get-arounds for Whisper’s voice activity detection deficiency with no supported solution
• older 2023 whisper produced repeat on encountering no-voice segments
• newer 2024 whisper outputs “[BLANK_AUDIO]“
• empirically, mostly-noise input audio never worked with whisper

Go allows to use float PCM directly:

• feeding ffmpeg audio code -ac 1 -ar 16k -c:a pcm_f32le — PCM 32-bit floating point little-endian
• that may solve the 32-bit header .wav problem
• possibly ffmpeg can then output samples prior to reading all audio using raw output to stdout -f f32le -
• raw ffmpeg files cannot be detected what they contain, how long they are or bitrate used

.

Second action is to move to turbo model of October 1 2024
openai/whisper#2363

• word error rate 18 for turbo over 28 for small en
• transcode speed measure 29× over 13×
• VRAM 6 GiB from 2 GiB https://www.reddit.com/r/LocalLLaMA/comments/1ft3wyb/comment/lpp1j5s/
• turbo may not be runnable on 8 GiB macOS 2021 M1

[resolutecake]

just noticed there is an option implemented for whisper.cpp/build/bin/main:
--no-speech-thold
— default value: 0.6 — data type: 32-bit signed float

— if audio quality is better or the model better, the model decides a segment is not speech with a higher probability
— such high probability leads to no transcoding being output
— if not speech probability is low, nonsense text may be output
— if it’s silence, voice activity detection will output “[BLANK_AUDIO]“

the option was added on 241223 hash 153757a
my checkout was 241214 therefore not having it

will be trying this first against my audio…

[resolutecake]

--no-speech-thold Doesn’t work

IT’S GENERALLY BROKEN:

.

as of whisper.cpp 250104 hash ece3ff8:

• Go bindings make was removed on migrating to cmake 241214
  Is the Go binding still being maintained? #2689
  Go library libwhisper.a no longer has a make target
• Go Discussion has notes that does not work
  Go #312

.

Whisper upstream:
Apparently whisper upstream has broken code for
non-speech silence or noise for 60–100 seconds
causing
transcode to leave out subsequent conversations of 1–5 minutes
instead
outputting [BLANK_AUDIO] by vad
and that
voice activity detection cannot be disabled

• never worked well

.

chunk-length tampering is discouraged:
reducing chunk length from 30 s to say 5 s
apparently leads to
increased duplicated lines or
bad word error rate

.

No serious solution:
People are using various fantastical detection-preprocessors producing

• timestamped segments fed into whisper
• because whisper only works reliably if there is actual speech in the audio
  as opposed to silence or noise

.

identifying noise as non-speech is difficult
and if whisper doesn’t feel like doing it, it’s even more difficult

.

sample complaint:
https://community.openai.com/t/whisper-leaves-out-chunks-of-speech-in-longer-transcript/715999

[resolutecake]

I tested different implementations of large-v3-turbo

on Apple: Mac mini (M1, Late 2020) 8GB 256GB GbEthernet macOS 15.2
with jfk sample, then
with a 4 h audio file, mostly noise

• regular large-v3-turbo: 7.133 s
• quantized large-v3-turbo: 3.202 s 55% faster
• Core ML large-v3-turbo: 2.148 s 70% faster
• Core ML M1 Max 1.849 s

noise handling is no better

transcoding where working is
significantly improved and
groups statements much better

the bad result is obtained much faster: 4 h is transcribed in 54 seconds at 263×
with small.en that was 90×, large-v3-turbo is 3 times faster with a 36% better word error rate performance

[resolutecake]

How to get to Core ML large-v3-turbo on macOS 15.2 250104 hash ece3ff8

— as brew
brew install anaconda
— as root
xcode-select --switch /Applications/Xcode.app/Contents/Developer
xcodebuild -license
— as user
export PATH=$(brew --prefix)/anaconda3/bin:$PATH
conda create -n py310-whisper python=3.10 -y
conda init zsh
— For changes to take effect, close and re-open your current shell.
zsh
export PATH=$(brew --prefix)/anaconda3/bin:$PATH
conda activate py310-whisper
pip install ane_transformers
pip install "numpy<2"
pip install torch==2.1.0
pip install openai-whisper
pip install coremltools
cd …whisper.cpp
./models/download-ggml-model.sh large-v3-turbo
./models/generate-coreml-model.sh large-v3-turbo
git pull
cmake -B build -DWHISPER_COREML=1
cmake --build build -j --config Release

— you’re in Core ML! The land of 263×
./build/bin/whisper-cli --model models/ggml-large-v3-turbo.bin --file samples/jfk.wav

whisper_init_state: loading Core ML model from '/opt/oth/whisper.cpp/models/ggml-large-v3-turbo-encoder.mlmodelc'
whisper_init_state: Core ML model loaded
system_info: … COREML = 1