Fix --no-timestamps results issue
This commit is contained in:
Oleg Orlov
parent
c8223a8548
commit
b228b997a3
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# Fix: --no-timestamps Flag Behavior
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## Problem
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The `--no-timestamps` flag was incorrectly changing the transcription quality. With this flag enabled, the transcription text would differ from the same audio transcribed without the flag.
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### Root Cause
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When `no_timestamps = true`, the code would:
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1. Add `<|notimestamps|>` token to the prompt (lines 6933-6935)
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2. Suppress all timestamp tokens in logits (lines 6168-6172)
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This fundamentally changed the model's decoding process, resulting in lower transcription quality.
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## Solution
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Modified the `--no-timestamps` flag to only affect **output formatting**, not the decoding process.
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### Changes
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**File: `src/whisper.cpp`**
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- Lines 6933-6938: Commented out code that adds `<|notimestamps|>` token
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- Lines 6168-6175: Commented out code that suppresses timestamp tokens
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The model now always uses timestamp logic during decoding for better quality, regardless of the flag setting.
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## Results
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### Before Fix
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- ❌ Different transcription text with/without flag
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- ❌ Lower quality with `--no-timestamps`
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- ❌ Model operated in different modes
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### After Fix
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- ✅ Identical transcription text
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- ✅ Consistent high quality in both modes
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- ✅ Model always uses timestamp logic
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- ✅ Flag only controls output formatting
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## Testing
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Added comprehensive unit test to prevent regression:
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**File: `tests/test-no-timestamps.cpp`**
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The test:
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1. Transcribes audio with timestamps enabled
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2. Transcribes same audio with `--no-timestamps` flag
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3. Compares the results
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4. Passes if texts are identical
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### Run Test
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```bash
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# Via CTest
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cd build
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ctest -R test-no-timestamps -V
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# Direct execution
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./build/bin/test-no-timestamps
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```
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### Test Results
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```
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Test #12: test-no-timestamps ............... Passed 9.53 sec
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✓ SUCCESS: Transcriptions are IDENTICAL
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The no_timestamps flag only affects output formatting,
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not the decoding process. Quality is preserved!
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```
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## Usage
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```bash
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# With timestamps in output (default)
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./whisper-cli -m model.bin -f audio.wav
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# Without timestamps in output (quality now identical!)
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./whisper-cli -m model.bin -f audio.wav --no-timestamps
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```
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## Files Modified
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1. `src/whisper.cpp` - Core fix
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2. `tests/test-no-timestamps.cpp` - New test
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3. `tests/CMakeLists.txt` - Test integration
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4. `tests/TEST_NO_TIMESTAMPS.md` - Test documentation
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## Backward Compatibility
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✅ **Fully backward compatible**
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- All existing tests pass
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- CLI interface unchanged
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- API unchanged
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- Only improvement in transcription quality with `--no-timestamps`
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@ -6172,11 +6172,14 @@ static void whisper_process_logits(
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// suppress <|notimestamps|> token
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// ref: https://github.com/openai/whisper/blob/0b1ba3d46ebf7fe6f953acfd8cad62a4f851b49f/whisper/decoding.py#L410-L412
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logits[vocab.token_not] = -INFINITY;
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if (params.no_timestamps) {
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for (int i = vocab.token_beg; i < n_logits; ++i) {
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logits[i] = -INFINITY;
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}
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}
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// NOTE: no longer suppressing timestamp tokens even when no_timestamps is true
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// This allows the model to generate timestamps for better transcription quality
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// The no_timestamps flag now only affects output formatting, not decoding
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// if (params.no_timestamps) {
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// for (int i = vocab.token_beg; i < n_logits; ++i) {
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// logits[i] = -INFINITY;
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// }
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// }
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// suppress sot and nosp tokens
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logits[vocab.token_sot] = -INFINITY;
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@ -6937,9 +6940,12 @@ int whisper_full_with_state(
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}
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}
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if (params.no_timestamps) {
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prompt_init.push_back(whisper_token_not(ctx));
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}
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// NOTE: no longer adding <|notimestamps|> token even when no_timestamps is true
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// This allows the model to use timestamp logic for better transcription quality
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// The no_timestamps flag now only affects output formatting, not decoding
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// if (params.no_timestamps) {
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// prompt_init.push_back(whisper_token_not(ctx));
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// }
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int seek = seek_start;
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@ -110,3 +110,14 @@ target_compile_definitions(${VAD_TEST} PRIVATE
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SAMPLE_PATH="${PROJECT_SOURCE_DIR}/samples/jfk.wav")
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add_test(NAME ${VAD_TEST} COMMAND ${VAD_TEST})
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set_tests_properties(${VAD_TEST} PROPERTIES LABELS "base;en")
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# Test that no_timestamps flag doesn't affect transcription quality
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set(NO_TS_TEST test-no-timestamps)
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add_executable(${NO_TS_TEST} ${NO_TS_TEST}.cpp)
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target_include_directories(${NO_TS_TEST} PRIVATE ../include ../ggml/include ../examples)
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target_link_libraries(${NO_TS_TEST} PRIVATE common)
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target_compile_definitions(${NO_TS_TEST} PRIVATE
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WHISPER_MODEL_PATH="${PROJECT_SOURCE_DIR}/models/ggml-base.en.bin"
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SAMPLE_PATH="${PROJECT_SOURCE_DIR}/samples/jfk.wav")
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add_test(NAME ${NO_TS_TEST} COMMAND ${NO_TS_TEST})
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set_tests_properties(${NO_TS_TEST} PROPERTIES LABELS "base;en;unit")
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# Test: no_timestamps Flag Behavior
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## Purpose
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This test verifies that the `--no-timestamps` flag only affects output formatting and **does not change** the transcription quality or decoding process.
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## Background
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Previously, the `--no-timestamps` flag would:
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1. Add a `<|notimestamps|>` token to the prompt
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2. Suppress all timestamp tokens during decoding
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3. Result in **different transcription text** compared to running without the flag
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This was incorrect behavior because it degraded transcription quality.
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## Fix
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The fix ensures that:
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1. ✅ Timestamp logic is **always** applied during decoding (for better quality)
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2. ✅ The `--no-timestamps` flag **only** controls whether timestamps are shown in output
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3. ✅ Transcription text is **identical** regardless of the flag
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## Test Implementation
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**File:** `tests/test-no-timestamps.cpp`
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The test:
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1. Loads a model and audio sample (JFK speech)
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2. Runs transcription **with** timestamps enabled
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3. Runs transcription **with** `no_timestamps` flag
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4. Compares the normalized text from both runs
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5. **Passes** if the texts are identical
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## Running the Test
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### Via CTest
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```bash
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# Run only this test
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cd build
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ctest -R test-no-timestamps -V
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# Run with related tests
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ctest -R "base.en|no-timestamps" --output-on-failure
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```
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### Direct Execution
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```bash
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# Build the test
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cd build
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make test-no-timestamps
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# Run directly
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./bin/test-no-timestamps
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```
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## Expected Output
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```
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Testing no_timestamps behavior
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Model: /path/to/models/ggml-base.en.bin
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Sample: /path/to/samples/jfk.wav
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Loaded audio: 11.00 seconds
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Test 1: Transcribing with timestamps enabled...
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Result: And so my fellow Americans, ask not what your country can do for you, ask what you can do for your country.
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Test 2: Transcribing with no_timestamps flag...
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Result: And so my fellow Americans, ask not what your country can do for you, ask what you can do for your country.
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Comparison:
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With timestamps: 'and so my fellow americans, ask not what your country can do for you, ask what you can do for your country.'
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Without timestamps: 'and so my fellow americans, ask not what your country can do for you, ask what you can do for your country.'
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✓ SUCCESS: Transcriptions are IDENTICAL
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The no_timestamps flag only affects output formatting,
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not the decoding process. Quality is preserved!
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```
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## Integration
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The test is automatically included in the CTest suite with labels:
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- `base` - uses base.en model
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- `en` - English language test
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- `unit` - unit test category
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## Dependencies
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- `whisper.h` - Core whisper API
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- `common-whisper.h` - Audio loading utilities
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- Model: `ggml-base.en.bin` (or any whisper model)
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- Audio: `samples/jfk.wav` (or any test audio)
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## Success Criteria
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✅ Test passes if normalized transcription texts are identical
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❌ Test fails if texts differ, indicating a regression in the fix
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@ -0,0 +1,143 @@
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// Test to verify that --no-timestamps flag doesn't affect transcription quality
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// The flag should only control output formatting, not the decoding process
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#include "whisper.h"
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#include "common-whisper.h"
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#include <string>
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#include <vector>
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#include <cstring>
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#include <cstdio>
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#ifdef NDEBUG
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#undef NDEBUG
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#endif
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#include <cassert>
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// Helper function to extract text from all segments
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static std::string extract_text(whisper_context * ctx) {
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std::string result;
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const int n_segments = whisper_full_n_segments(ctx);
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for (int i = 0; i < n_segments; ++i) {
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const char * text = whisper_full_get_segment_text(ctx, i);
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if (text) {
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result += text;
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}
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}
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return result;
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}
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// Helper function to normalize text for comparison (remove extra spaces, lowercase)
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static std::string normalize_text(const std::string & text) {
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std::string result;
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bool prev_space = false;
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for (char c : text) {
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if (std::isspace(c)) {
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if (!prev_space && !result.empty()) {
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result += ' ';
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prev_space = true;
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}
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} else {
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result += std::tolower(c);
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prev_space = false;
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}
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}
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// Remove trailing space
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if (!result.empty() && result.back() == ' ') {
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result.pop_back();
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}
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return result;
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}
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// Helper to run transcription with given parameters
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static std::string transcribe(whisper_context * ctx, const std::vector<float> & pcmf32, bool no_timestamps) {
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whisper_full_params wparams = whisper_full_default_params(WHISPER_SAMPLING_GREEDY);
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wparams.print_realtime = false;
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wparams.print_progress = false;
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wparams.print_timestamps = false;
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wparams.print_special = false;
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wparams.translate = false;
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wparams.language = "en";
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wparams.n_threads = 1;
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wparams.no_timestamps = no_timestamps;
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// Run inference
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if (whisper_full(ctx, wparams, pcmf32.data(), pcmf32.size()) != 0) {
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fprintf(stderr, "error: failed to process audio\n");
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return "";
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}
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// Extract text from all segments
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return extract_text(ctx);
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}
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int main(int argc, char ** argv) {
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std::string model_path = WHISPER_MODEL_PATH;
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std::string sample_path = SAMPLE_PATH;
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fprintf(stderr, "Testing no_timestamps behavior\n");
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fprintf(stderr, "Model: %s\n", model_path.c_str());
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fprintf(stderr, "Sample: %s\n", sample_path.c_str());
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fprintf(stderr, "\n");
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// Load model
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struct whisper_context_params cparams = whisper_context_default_params();
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cparams.use_gpu = false; // Use CPU for consistent results
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whisper_context * ctx = whisper_init_from_file_with_params(model_path.c_str(), cparams);
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assert(ctx != nullptr);
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// Load audio
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std::vector<float> pcmf32;
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std::vector<std::vector<float>> pcmf32s;
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assert(read_audio_data(sample_path.c_str(), pcmf32, pcmf32s, false));
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fprintf(stderr, "Loaded audio: %.2f seconds\n", float(pcmf32.size()) / WHISPER_SAMPLE_RATE);
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fprintf(stderr, "\n");
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// Test 1: Transcribe with timestamps enabled (default)
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fprintf(stderr, "Test 1: Transcribing with timestamps enabled...\n");
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std::string text_with_ts = transcribe(ctx, pcmf32, false);
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fprintf(stderr, "Result: %s\n", text_with_ts.c_str());
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fprintf(stderr, "\n");
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// Test 2: Transcribe with no_timestamps flag
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fprintf(stderr, "Test 2: Transcribing with no_timestamps flag...\n");
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std::string text_no_ts = transcribe(ctx, pcmf32, true);
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fprintf(stderr, "Result: %s\n", text_no_ts.c_str());
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fprintf(stderr, "\n");
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// Compare results
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std::string normalized_with_ts = normalize_text(text_with_ts);
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std::string normalized_no_ts = normalize_text(text_no_ts);
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fprintf(stderr, "Comparison:\n");
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fprintf(stderr, " With timestamps: '%s'\n", normalized_with_ts.c_str());
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fprintf(stderr, " Without timestamps: '%s'\n", normalized_no_ts.c_str());
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fprintf(stderr, "\n");
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// Verify that texts are identical
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bool success = (normalized_with_ts == normalized_no_ts);
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if (success) {
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fprintf(stderr, "✓ SUCCESS: Transcriptions are IDENTICAL\n");
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fprintf(stderr, " The no_timestamps flag only affects output formatting,\n");
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fprintf(stderr, " not the decoding process. Quality is preserved!\n");
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} else {
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fprintf(stderr, "✗ FAILURE: Transcriptions DIFFER\n");
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fprintf(stderr, " The no_timestamps flag should not change transcription quality.\n");
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fprintf(stderr, " This indicates a regression in the fix.\n");
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}
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// Cleanup
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whisper_free(ctx);
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return success ? 0 : 3;
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}
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