player: fix --lavfi-complex freeze

Commit 0e0b87b6f3297 fixed that dropped packets did not trigger further
work correctly. But it also made trivial --lavfi-complex freeze. The
reason is that the meaning if DATA_AGAIN was overloaded: the decoders
meant that they should be called again, while lavfi.c meant that other
outputs needed to be checked again. Rename the latter meaning to
DATA_STARVE, which means that the current input will deliver no more
data, until "other" work has been done (like reading other outputs, or
feeding input).

The decoders never return DATA_STARVE, because they don't get input from
the player core (instead, they get it from the demuxer directly, which
is why they still can return DATA_WAIT).

Also document the DATA_* semantics in the enum.

Fixes #4746.

1 files changed, 5 insertions, 4 deletions

diff --git a/common/common.h b/common/common.h
index cdd1d56ed5..bed9060f71 100644
--- a/common/common.h
+++ b/common/common.h
@@ -59,10 +59,11 @@ enum stream_type {
 };
 
 enum {
-    DATA_OK     = 1,
-    DATA_WAIT   = 0,
-    DATA_AGAIN  = -1,
-    DATA_EOF    = -2,
+    DATA_OK     = 1,        // data is actually being returned
+    DATA_WAIT   = 0,        // async wait: check state again after next wakeup
+    DATA_AGAIN  = -2,       // repeat request (internal progress was made)
+    DATA_STARVE = -1,       // need input (might require to drain other outputs)
+    DATA_EOF    = -3,       // no more data available
 };
 
 extern const char mpv_version[];