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, 5 insertions, 3 deletions

diff --git a/audio/decode/ad_lavc.c b/audio/decode/ad_lavc.c
index cb8cfa8c82..4ff69c3f20 100644
--- a/audio/decode/ad_lavc.c
+++ b/audio/decode/ad_lavc.c
@@ -309,8 +309,10 @@ static int decode_packet(struct dec_audio *da)
     mp_audio_set_null_data(&da->decoded);
 
     struct demux_packet *mpkt = priv->packet;
-    if (!mpkt)
-        mpkt = demux_read_packet(da->header);
+    if (!mpkt) {
+        if (demux_read_packet_async(da->header, &mpkt) == 0)
+            return AD_WAIT;
+    }
 
     priv->packet = talloc_steal(priv, mpkt);
 
@@ -343,7 +345,7 @@ static int decode_packet(struct dec_audio *da)
         }
         // LATM may need many packets to find mux info
         if (ret == AVERROR(EAGAIN))
-            return 0;
+            return AD_OK;
     }
     if (ret < 0) {
         MP_ERR(da, "Error decoding audio.\n");