ao_pipewire: fix delay calculation

A figure from pipewire documentation:

```
           stream time domain           graph time domain
         /-----------------------\/-----------------------------\

 queue     +-+ +-+  +-----------+                 +--------+
 ---->     | | | |->| converter | ->   graph  ->  | kernel | -> speaker
 <----     +-+ +-+  +-----------+                 +--------+
 dequeue   buffers                \-------------------/\--------/
                                     graph              internal
                                    latency             latency
         \--------/\-------------/\-----------------------------/
           queued      buffered            delay
```

We calculate `end_time` in the following steps:

1. get current timestamp in mpv
```
int64_t end_time = mp_time_ns();
```

2. add duration of samples to enqueue
```
end_time += MP_TIME_S_TO_NS(nframes) / ao->samplerate;
```

3. add delay of the pipewire graph
```
end_time += MP_TIME_S_TO_NS(time.delay) * time.rate.num / time.rate.denom;
```

4. add duration of queued and buffered samples.
```
end_time += MP_TIME_S_TO_NS(time.queued) / ao->samplerate;
end_time += MP_TIME_S_TO_NS(time.buffered) / ao->samplerate;
```
New in this commit. `time.queued` is usually zero as `SPA_PARAM_BUFFERS_buffers`
is default to 1; however it is not always.
`time.buffered` is non-zero if there is a resampler involved.

5. add elapsed duration from when `time` is captured
```
end_time -= pw_stream_get_nsec(p->stream) - time.now;
```
New in this commit. `time` is captured at `time.now`.
From then, time has passed so we need to exclude the elapsed time,
by calculating the diff of `pw_stream_get_nsec()` and `time.now`.

0 files changed, 0 insertions, 0 deletions