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`.

1 files changed, 16 insertions, 3 deletions

diff --git a/audio/out/ao_pipewire.c b/audio/out/ao_pipewire.c
index 9e08ddc626..94d393a26d 100644
--- a/audio/out/ao_pipewire.c
+++ b/audio/out/ao_pipewire.c
@@ -47,6 +47,15 @@ static inline int pw_stream_get_time_n(struct pw_stream *stream, struct pw_time
 #define spa_hook_remove(hook) if ((hook)->link.prev) spa_hook_remove(hook)
 #endif
 
+#if !PW_CHECK_VERSION(1, 0, 4)
+static uint64_t pw_stream_get_nsec(struct pw_stream *stream)
+{
+	struct timespec ts;
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	return SPA_TIMESPEC_TO_NSEC(&ts);
+}
+#endif
+
 enum init_state {
     INIT_STATE_NONE,
     INIT_STATE_SUCCESS,
@@ -189,9 +198,13 @@ static void on_process(void *userdata)
         time.rate.num = 1;
 
     int64_t end_time = mp_time_ns();
-    /* time.queued is always going to be 0, so we don't need to care */
-    end_time += (nframes * 1e9 / ao->samplerate) +
-                ((double) time.delay * SPA_NSEC_PER_SEC * time.rate.num / time.rate.denom);
+    end_time += MP_TIME_S_TO_NS(nframes) / ao->samplerate;
+    end_time += MP_TIME_S_TO_NS(time.delay) * time.rate.num / time.rate.denom;
+    end_time += MP_TIME_S_TO_NS(time.queued) / ao->samplerate;
+#if PW_CHECK_VERSION(0, 3, 50)
+    end_time += MP_TIME_S_TO_NS(time.buffered) / ao->samplerate;
+#endif
+    end_time -= pw_stream_get_nsec(p->stream) - time.now;
 
     int samples = ao_read_data_nonblocking(ao, data, nframes, end_time);
     b->size = samples;