| # Final Aligner Selection |
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| Decision: `SELECTED_MFA` (2026-09-06). |
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| This decision supersedes the 2026-09-04 `SELECTED_WHISPERX` operational choice after the |
| previously missing strict MFA full-36 evaluation was completed. Historical Stage 5 evidence |
| remains unchanged. |
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| MFA, WhisperX, and NeMo now all have successful 36/36 candidates. On the five rows with |
| manual first-word gold, MFA and WhisperX remain effectively tied: MFA first-word-end MAE is |
| 0.0162 s (median 0.0110, max 0.0300), while WhisperX is 0.0154 s (median 0.0140, |
| max 0.0310). NeMo is 0.2210 s with a 0.9200 s maximum error on EN0949. |
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| Across all 36 rows, MFA and WhisperX differ by at least 0.250 s on 7 rows, versus 28 for |
| MFA/NeMo and 32 for WhisperX/NeMo. MFA and WhisperX are especially close at first-word |
| boundaries (mean absolute differences 0.059306 s start and 0.018694 s end). Their material |
| disagreements are concentrated at last-word boundaries. On the largest disputed cases, |
| retained MFA forced-alignment evidence and independent NeMo last-boundary timings support |
| the later MFA placements. This is diagnostic evidence rather than manual ground truth. |
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| The canonical final output is `results/final/final-annotated-36.csv` with SHA-256 |
| `37bcb85fc22fb142dae40453b90dd3b427bbfd657861bee7529cd433915535a8` and is byte-identical to |
| `results/postfinal/mfa-full-36/annotated-36-mfa.csv`. |
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| ## Limitations |
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| - Manual gold covers only `first_word_text` and `first_word_end_s` on five rows. |
| - First-word start and both last-word boundaries have no manual ground truth. |
| - Pairwise agreement is not accuracy. |
| - The 0.0008 s MFA/WhisperX five-row MAE difference is too small to rank the systems by itself. |
| - Runtime results are from different hosts/cache states and are secondary evidence. |
| - This selection is an operational choice from the available evidence, not a claim of universal timing superiority. |
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