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Audio engine requirements
Real-time callback rules
The callback must not allocate/free memory, lock blocking mutexes, perform filesystem/network/console I/O, log, load plugins or samples, call GUI APIs, or wait for another thread.
Use preallocated buffers and bounded work. Publish parameter and graph changes through a documented real-time-safe mechanism. Verify atomics are lock-free where required on the target platform.
Processing model
Process a bounded number of frames per block. Do not assume a fixed block size unless the backend guarantees it. Define maximum frame and event counts and safe behavior when those limits are reached.
The initial milestone is offline processing, then a test oscillator -> gain -> meter/output graph, then a hardware backend.
Clock and transport
Audio sample position is the authoritative playback clock. Use integer or rational timeline representations to avoid cumulative floating-point drift. Define tempo-map conversion and behavior at tempo changes before implementing tempo automation.