ao: add ao_play_silence, use for ao_alsa and ao_oss

Also add a corresponding function to audio/format.c, which fills an
audio block with silence.

1 files changed, 6 insertions, 0 deletions

diff --git a/audio/format.c b/audio/format.c
index b933d07e16..448b670671 100644
--- a/audio/format.c
+++ b/audio/format.c
@@ -127,3 +127,9 @@ int af_str2fmt_short(bstr str)
     }
     return 0;
 }
+
+void af_fill_silence(void *dst, size_t bytes, int format)
+{
+    bool us = (format & AF_FORMAT_SIGN_MASK) == AF_FORMAT_US;
+    memset(dst, us ? 0x80 : 0, bytes);
+}