audio: change playback restart and resyncing

This commit makes audio decoding non-blocking. If e.g. the network is
too slow the playloop will just go to sleep, instead of blocking until
enough data is available.

For video, this was already done with commit 7083f88c. For audio, it's
unfortunately much more complicated, because the audio decoder was used
in a blocking manner. Large changes are required to get around this.
The whole playback restart mechanism must be turned into a statemachine,
especially since it has close interactions with video restart. Lots of
video code is thus also changed.

(For the record, I don't think switching this code to threads would
make this conceptually easier: the code would still have to deal with
external input while blocked, so these in-between states do get visible
[and thus need to be handled] anyway. On the other hand, it certainly
should be possible to modularize this code a bit better.)

This will probably cause a bunch of regressions.

1 files changed, 19 insertions, 7 deletions

diff --git a/player/core.h b/player/core.h
index adb9185da0..8789060ce8 100644
--- a/player/core.h
+++ b/player/core.h
@@ -149,6 +149,22 @@ enum {
     VD_WAIT = 3,        // no EOF, but no output; wait until wakeup
 };
 
+/* Note that playback can be paused, stopped, etc. at any time. While paused,
+ * playback restart is still active, because you want seeking to work even
+ * if paused.
+ * The main purpose of distinguishing these states is proper reinitialization
+ * of A/V sync.
+ */
+enum playback_status {
+    // code may compare status values numerically
+    STATUS_SYNCING,     // seeking for a position to resume
+    STATUS_FILLING,     // decoding more data (so you start with full buffers)
+    STATUS_READY,       // buffers full, playback can be started any time
+    STATUS_PLAYING,     // normal playback
+    STATUS_DRAINING,    // decoding has ended; still playing out queued buffers
+    STATUS_EOF,         // playback has ended, or is disabled
+};
+
 #define NUM_PTRACKS 2
 
 typedef struct MPContext {
@@ -234,16 +250,11 @@ typedef struct MPContext {
 
     struct vo *video_out;
 
-    /* We're starting playback from scratch or after a seek. Show first
-     * video frame immediately and reinitialize sync. */
-    bool restart_playback;
+    enum playback_status video_status, audio_status;
+    bool restart_complete;
     /* Set if audio should be timed to start with video frame after seeking,
      * not set when e.g. playing cover art */
     bool sync_audio_to_video;
-    /* After playback restart (above) or audio stream change, adjust audio
-     * stream by cutting samples or adding silence at the beginning to make
-     * audio playback position match video position. */
-    bool syncing_audio;
     bool hrseek_active;
     bool hrseek_framedrop;
     double hrseek_pts;
@@ -465,6 +476,7 @@ void run_playloop(struct MPContext *mpctx);
 void idle_loop(struct MPContext *mpctx);
 void handle_force_window(struct MPContext *mpctx, bool reconfig);
 void add_frame_pts(struct MPContext *mpctx, double pts);
+void finish_playback_restart(struct MPContext *mpctx);
 
 // scripting.c
 struct mp_scripting {