struct PacketMixState

Start mixing the packet at the front of the mix queue.

Returns nullopt if the queue is empty.

The returned PacketMixState object contains bookkeeping information about the mix.

The caller should update this state as necessary and pass that final updated state

to FinishMixerJob once this mix operation is ready. If the mix operation only partially

fills the packet, then the next call to NextMixerJob will return the same state that

was passed to FinishMixerJob (except with an updated mix_target).

For example, a typical usage might look like:

while (true) {

auto mix_state = pq->NextMixerJob();

if (mix_state.capture_timestamp == NO_TIMESTAMP) {

mix_state.capture_timestamp = current_timestamp;

}

if (mix_state.frames > max_mix_frames) {

mix_state.frames = max_mix_frames;

}

mix(mix_state.target, mix_state.frames);

pq->FinishMixerJob(mix_state);

}