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Upgrade translation model to NLLB-200-distilled-1.3B - #12

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etiennechabert merged 7 commits into
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feature/upgrade-nllb-translation-model
Mar 16, 2026
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etiennechabert merged 7 commits into
mainfrom
feature/upgrade-nllb-translation-model

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@etiennechabert etiennechabert commented Mar 16, 2026 •

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Summary

Upgrade from M2M100_1.2B to the more modern NLLB-200-distilled-1.3B translation model for better quality without requiring additional resources.

What's Changing

Translation Model Upgrade

Old: facebook/m2m100_1.2B (2020, 1.2B parameters, ~5GB VRAM)
New: facebook/nllb-200-distilled-1.3B (2022, 1.3B parameters, ~5GB VRAM)

Benefits

  • ✅ More modern architecture - NLLB (2022) vs M2M100 (2020)
  • ✅ Better translation quality - Improved accuracy for all 200 languages
  • ✅ Same VRAM footprint - Still ~5GB, no additional resources needed
  • ✅ Similar speed - ~4-5s per translation (same as before)
  • ✅ Safe upgrade - No performance trade-offs

Why distilled-1.3B instead of 3.3B?

  • 💡 Conservative choice - Same resources, better quality
  • ⚡ Same speed - No slowdown in translation
  • 📊 VRAM headroom - Leaves room for future upgrades
  • 🎯 Best balance - Quality improvement without sacrificing performance

Technical Changes

Config (config.py)

  • Updated TRANSLATION_MODEL default to facebook/nllb-200-distilled-1.3B
  • Added NLLB_LANG_CODE_MAP for language code conversion
  • Added get_translation_lang_code() classmethod to handle mapping
  • Documented all translation model options with VRAM estimates
  • Marked distilled-1.3B as RECOMMENDED

Backend (app.py)

  • Switched from M2M100-specific imports to AutoTokenizer/AutoModelForSeq2SeqLM
  • Updated translate_text() to use NLLB language codes (e.g., eng_Latn, deu_Latn)
  • Backward compatible with M2M100 if user switches back

Language Code Mapping

NLLB uses different codes than M2M100:

  • English: en → eng_Latn
  • German: de → deu_Latn
  • Spanish: es → spa_Latn
  • French: fr → fra_Latn
  • etc.

The mapping is handled automatically via Config.get_translation_lang_code().

VRAM Impact

Before:

  • Whisper (turbo): ~6GB
  • Translation (m2m100_1.2B): ~5GB
  • Diarization: ~2-3GB
  • Total: ~13-14GB

After (SAME!):

  • Whisper (turbo): ~6GB
  • Translation (nllb-200-distilled-1.3B): ~5GB ✅
  • Diarization: ~2-3GB
  • Total: ~13-14GB

Testing Notes

When testing:

  1. First run will download the new model (~2.6GB)
  2. Same translation speed (~4-5s per segment)
  3. Better translation quality, especially for complex sentences
  4. Works with all existing language configurations

Future Upgrades Available

With VRAM headroom still available, future options include:

  • Upgrade to NLLB-200-3.3B for even better quality (+3GB VRAM, slower)
  • Upgrade Whisper to large-v3 for better transcription (+4GB VRAM)

🤖 Generated with Claude Code

Replace M2M100_1.2B with facebook/nllb-200-distilled-1.3B:
- Similar size (1.2B → 1.3B parameters)
- Same VRAM footprint (~5GB)
- Better translation quality with more modern architecture (2022)
- Supports 200 languages with improved accuracy
- Similar speed (~4-5s per segment)

This is a safe upgrade that improves quality without requiring more resources.

Changes:
- Updated TRANSLATION_MODEL default to nllb-200-distilled-1.3B
- Added NLLB language code mapping (eng_Latn, deu_Latn, etc.)
- Added get_translation_lang_code() method to handle code conversion
- Switched from M2M100-specific imports to AutoTokenizer/AutoModel
- Updated translate_text() to use mapped language codes

Expected VRAM usage: ~13-14GB total (same as before)
Expected performance: ~4-5s per translation (similar to m2m100)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
@etiennechabert
etiennechabert force-pushed the feature/upgrade-nllb-translation-model branch from 618e072 to f69523f Compare March 16, 2026 18:21
@etiennechabert etiennechabert changed the title Upgrade translation model to NLLB-200-3.3B for better quality Upgrade translation model to NLLB-200-distilled-1.3B Mar 16, 2026
etiennechabert and others added 6 commits March 16, 2026 19:30
NLLB tokenizers use lang_code_to_id dictionary instead of get_lang_id() method.
Added compatibility check to support both NLLB and M2M100 tokenizers.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Use try-except approach instead of hasattr for more robust tokenizer detection.
Also properly handle src_lang parameter for NLLB tokenizers.

Changes:
- NLLB: Pass src_lang as parameter to tokenizer call
- M2M100: Set src_lang as tokenizer attribute
- Try lang_code_to_id first, fall back to get_lang_id
- Better error message if neither method works

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
NLLB tokenizers use the same approach as M2M100:
set src_lang as an attribute, not as a parameter.

Both NLLB and M2M100 tokenizers:
- Set tokenizer.src_lang = src_code (attribute)
- Use lang_code_to_id (NLLB) or get_lang_id() (M2M100) for target

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Frontend changes:
- Removed extra languages from admin.html (only EN, DE)
- Removed extra languages from viewer.html (only EN, DE)
- Updated language flags mapping to match

Backend changes:
- Added debug logging to show available NLLB language codes
- Will help identify correct language code format for NLLB tokenizer

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Print available language codes when loading NLLB tokenizer to help
identify the correct code format. Will show at startup which codes
are available and whether our expected codes exist.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
- Use convert_tokens_to_ids() instead of lang_code_to_id attribute
- Update startup debug to test language codes correctly
- Fixes translation errors with eng_Latn and deu_Latn codes

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
@etiennechabert
etiennechabert merged commit 6d19b95 into main Mar 16, 2026
2 of 6 checks passed
@etiennechabert
etiennechabert deleted the feature/upgrade-nllb-translation-model branch March 16, 2026 19:06
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