D819 - Audio output plays on a host device through a sink

Status: decided Date: 2026-10-12

orbistoun-audio hands each chunk a guest's output port plays to a sink, at guest semantics: the port, its channel count, and 16-bit samples at 48 kHz. The sink answers how long the output call waits. orbistoun-audio-host is the one sink: every port has a queue, and the device's callback mixes the queues into whatever rate and channel layout the device runs at. The worker installs it when ORBISTOUN_AUDIO=host, which the window sets for the runs it plays. With no sink installed, a port paces itself by its sample rate, as before.

The output call waits until its port holds no more than about 64 ms, never longer than two chunks. The guest is then paced by the device's clock. Pacing by a sleep while a device drained the queue would let the two clocks drift apart, and on a host whose timer ticks every 15.6 ms a sleep overshoots badly enough to empty the queue. The logical clock still advances by the samples' duration, so a guest timing its output sees the same time either way.

Only selectors 0 and 1 are played. Their format, 16-bit signed interleaved, is assumed from oops-sdk: its audio.c opens with selector 1 as "16-bit signed interleaved stereo" and plays on hardware. Selector 2 opens two channels as measured, but its format is unmeasured, so its samples reach no sink. sceAudioOutOutputs and sceAudioOut2ContextPush reach none either; the run report names output that went unheard, and output that played nowhere because the device did not open.

Why: a title with audio was silent, and nothing in a run said so. The seam keeps the host audio library out of orbistoun-audio, as orbistoun-gpu stays clear of ash. A second backend is then another sink, and the port's contract is tested with a sink that records what it is handed. A command-line run stays silent unless asked: the loop runs titles unattended, and many at once.

Rejected:

• Keeping the sleep and pushing samples alongside it: the queue drifts empty or full with the host's timer, and the guest's pacing stops meaning anything about the device.
• A device opened by orbistoun-audio itself: it ties the guest-facing crate to one host library, and its tests to a host with a sound card.
• Linux and macOS in the same change: cpal links the system's ALSA library on Linux, a build dependency every Unix image would carry. It is Windows-only, as host gamepads are.