[vlc-devel] [RFC PATCH 12/13] FIXUP: fix preroll with !pulse aouts

[Thomas Guillem]

The idea here is a play a silence corresponding to the difference between the
first system pts and now. This will be used for aouts that can't start corked,
so every aout modules except PulseAudio. To reach this new code path, aout
modules need to return a valid value from the first pf_get_time callback
(already the case of main modules).
---
 src/audio_output/aout_internal.h |  1 +
 src/audio_output/dec.c           | 54 ++++++++++++++++++++++----------
 2 files changed, 38 insertions(+), 17 deletions(-)

diff --git a/src/audio_output/aout_internal.h b/src/audio_output/aout_internal.h
index 55fab1a7e9..42d0f1ff35 100644
--- a/src/audio_output/aout_internal.h
+++ b/src/audio_output/aout_internal.h
@@ -72,6 +72,7 @@ typedef struct
 
     struct
     {
+        bool is_first;
         vlc_tick_t end; /**< Last seen PTS */
         struct vlc_clock_t *clock;
         float rate; /**< Play-out speed rate */
diff --git a/src/audio_output/dec.c b/src/audio_output/dec.c
index 523682e619..8a2808c5a0 100644
--- a/src/audio_output/dec.c
+++ b/src/audio_output/dec.c
@@ -102,6 +102,7 @@ error:
         return -1;
     }
 
+    owner->sync.is_first = true;
     owner->sync.rate = 1.f;
     owner->sync.end = VLC_TS_INVALID;
     owner->sync.resamp_type = AOUT_RESAMPLING_NONE;
@@ -229,8 +230,8 @@ static void aout_DecSilence (audio_output_t *aout, vlc_tick_t length, vlc_tick_t
                vlc_clock_ConvertToSystem(owner->sync.clock, vlc_tick_now(), pts));
 }
 
-static void aout_DecSynchronize(audio_output_t *aout, vlc_tick_t system_now,
-                                vlc_tick_t dec_pts)
+static vlc_tick_t aout_DecSynchronize(audio_output_t *aout, vlc_tick_t system_now,
+                                   block_t *block)
 {
     /**
      * Depending on the drift between the actual and intended playback times,
@@ -248,11 +249,39 @@ static void aout_DecSynchronize(audio_output_t *aout, vlc_tick_t system_now,
      * all samples in the buffer will have been played. Then:
      *    pts = vlc_tick_now() + delay
      */
+    aout_owner_t *owner = aout_owner (aout);
     vlc_tick_t delay;
-    if (aout->time_get(aout, &delay) != 0)
-        return; /* nothing can be done if timing is unknown */
+    if (aout->time_get(aout, &delay) == 0)
+    {
+        if (owner->sync.is_first)
+        {
+            vlc_tick_t system_pts =
+                vlc_clock_ConvertToSystem(owner->sync.clock, system_now + delay,
+                                          block->i_pts);
+            vlc_tick_t silence_delay = system_pts - system_now;
+            if (silence_delay > 0)
+                aout_DecSilence (aout, silence_delay, block->i_pts);
+            if (aout->time_get(aout, &delay) == 0)
+                aout_RequestRetiming(aout, system_now + delay, block->i_pts);
+        }
+        else
+            aout_RequestRetiming(aout, system_now + delay, block->i_pts);
+    }
+
+    if (owner->sync.delay != 0)
+    {
+        block->i_pts += owner->sync.delay;
+        block->i_dts += owner->sync.delay;
+    }
 
-    aout_RequestRetiming(aout, system_now, dec_pts - delay);
+    vlc_tick_t system_pts = vlc_clock_ConvertToSystem(owner->sync.clock, system_now,
+                                                   block->i_pts);
+
+    owner->sync.end = block->i_pts + block->i_length + 1;
+    owner->sync.discontinuity = false;
+    owner->sync.is_first = false;
+
+    return system_pts;
 }
 
 void aout_RequestRetiming(audio_output_t *aout, vlc_tick_t system_ts,
@@ -397,20 +426,10 @@ int aout_DecPlay(audio_output_t *aout, block_t *block)
     }
 
     /* Drift correction */
-    vlc_tick_t system_now = vlc_tick_now();
-    aout_DecSynchronize(aout, system_now, block->i_pts);
-
-    if (owner->sync.delay != 0)
-    {
-        block->i_pts += owner->sync.delay;
-        block->i_dts += owner->sync.delay;
-    }
+    vlc_tick_t system_pts = aout_DecSynchronize(aout, vlc_tick_now(), block);
 
     /* Output */
-    owner->sync.end = block->i_pts + block->i_length + 1;
-    owner->sync.discontinuity = false;
-    aout->play(aout, block, vlc_clock_ConvertToSystem(owner->sync.clock, system_now,
-                                                      block->i_pts));
+    aout->play(aout, block, system_pts);
     atomic_fetch_add_explicit(&owner->buffers_played, 1, memory_order_relaxed);
     return ret;
 drop:
@@ -473,6 +492,7 @@ void aout_DecFlush (audio_output_t *aout, bool wait)
 {
     aout_owner_t *owner = aout_owner (aout);
 
+    owner->sync.is_first = true;
     owner->sync.end = VLC_TS_INVALID;
     if (owner->mixer_format.i_format)
     {
-- 
2.18.0