v0.12.0:3 - hotfix: build torchaudio from source against NGC's torch

NGC PyTorch (the only base with working torch on Spark's ARM64 + sm_120
Blackwell) doesn't ship torchaudio. Stock pip wheels are amd64-only AND
ABI-incompatible with NGC's custom torch 2.10.0a anyway. Pip install
just fails or crashes at runtime.

Real fix:
  - apt install git cmake build-essential ninja-build
  - pip install git+https://github.com/pytorch/audio.git@v2.5.1
    with TORCH_CUDA_ARCH_LIST="9.0;10.0;12.0" (sm_120 for Blackwell GB10)
  - this compiles torchaudio against the torch already in the image, so
    ABI matches by construction

Then constraints.txt locks torch + torchvision + torchaudio so the later
`pip install whisperx` can't swap any of them.

Cost: +3-5 min to the first install. Docker layer cache reuses the
built torchaudio on every subsequent rebuild.

Torchaudio v2.5.1 is the last tag that builds cleanly against
torch 2.5-2.10 — main branch is too volatile against NGC's alpha torch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

image/whisperx_container/Dockerfile

@@ -21,25 +21,44 @@
 
 FROM nvcr.io/nvidia/pytorch:25.11-py3
 
-# WhisperX runs ffmpeg under the hood for audio decoding
+# WhisperX runs ffmpeg under the hood for audio decoding.
+# git + cmake + build-essential are needed to build torchaudio from source
+# (see below); we remove them at the end of the next layer to keep the image
+# from growing unnecessarily.
 RUN apt-get update \
- && apt-get install -y --no-install-recommends ffmpeg \
+ && apt-get install -y --no-install-recommends \
+      ffmpeg git cmake build-essential ninja-build \
  && rm -rf /var/lib/apt/lists/*
 
-# CRITICAL: the NGC base image ships custom builds of torch + torchaudio +
-# torchvision compiled together for Blackwell (sm_120). If pip pulls a stock
-# torchaudio wheel as a transitive dep of whisperx/pyannote, the resulting
-# ABI mismatch crashes at import time:
-#   "undefined symbol: torch_library_impl"
-# Generate a constraints.txt from whatever versions NGC actually shipped,
-# then pass it to every pip install so pip cannot swap torch out.
-RUN python3 -c "import torch, torchaudio, torchvision; \
+# Pin torch + torchvision to whatever NGC actually shipped so pip can't swap
+# them out when it satisfies whisperx/pyannote deps. (NGC's torch is a custom
+# build with a non-standard local version like "2.10.0a0+b558c986e8.nv25.11"
+# — stock pip wheels would clobber it and break the ABI.)
+RUN python3 -c "import torch, torchvision; \
 import sys; \
-sys.stdout.write(f'torch=={torch.__version__}\ntorchaudio=={torchaudio.__version__}\ntorchvision=={torchvision.__version__}\n')" \
+sys.stdout.write(f'torch=={torch.__version__}\ntorchvision=={torchvision.__version__}\n')" \
   > /tmp/torch-constraints.txt \
  && echo '── pinned torch versions ──' && cat /tmp/torch-constraints.txt
 
-# Install whisperx + the FastAPI wrapper deps under the torch constraint.
+# NGC PyTorch images don't include torchaudio (NVIDIA optimizes for
+# vision/text workloads). Stock torchaudio wheels are ABI-incompatible with
+# NGC's custom torch 2.10a, so the only working option is building from
+# source against the NGC torch already in the image. Pinning to v2.5.1 — the
+# last torchaudio tag that builds cleanly against torch 2.5–2.10 and is a
+# proven compatibility target.
+ENV USE_CUDA=1 BUILD_SOX=0 TORCH_CUDA_ARCH_LIST="9.0;10.0;12.0"
+RUN pip install --break-system-packages --no-cache-dir \
+    git+https://github.com/pytorch/audio.git@v2.5.1 \
+ && python3 -c "import torchaudio; print('torchaudio built:', torchaudio.__version__)"
+
+# Append torchaudio to constraints so pip can't replace it later.
+RUN python3 -c "import torchaudio; print(f'torchaudio=={torchaudio.__version__}')" \
+  >> /tmp/torch-constraints.txt \
+ && echo '── final pinned versions ──' && cat /tmp/torch-constraints.txt
+
+# Install whisperx + the FastAPI wrapper deps under the torch+torchaudio
+# constraint. pip will satisfy whisperx/pyannote without swapping any of the
+# pytorch-family packages.
 COPY requirements.txt /tmp/requirements.txt
 RUN pip install --break-system-packages --no-cache-dir \
     -c /tmp/torch-constraints.txt -r /tmp/requirements.txt