Previous attempt allocated DirectByteBuffer as local variables inside
runCapture/runPlayout. ART's JIT On-Stack Replacement nulled them
when recompiling the hot loop mid-execution.
Fix: allocate as class fields on AudioPipeline (captureDirectBuf,
playoutDirectBuf). Object fields live on the heap, immune to OSR
stack frame replacement.
Eliminates JNI array copies (GetShortArrayRegion/SetShortArrayRegion)
from the audio hot path, preventing ART GC SIGBUS crashes on
Android 16 with concurrent mark-compact GC.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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