dvd: flush buffers properly on seek

Suggested by tholin on github issue #882.

This is not entirely clean, but the fields we're accessing might be
considered internal to libavformat. On the other hand, existence of the
fields is guaranteed by the ABI, and nothing in the libavformat doxygen
suggestes they're not allowed to be accessed.

CC: @mpv-player/stable

1 files changed, 4 insertions, 3 deletions

diff --git a/demux/demux_lavf.c b/demux/demux_lavf.c
index e922708626..71f3f62e85 100644
--- a/demux/demux_lavf.c
+++ b/demux/demux_lavf.c
@@ -1009,11 +1009,12 @@ redo:
          * call the new API instead of relying on av_seek_frame() to do this
          * for us.
          */
-        stream_drop_buffers(demuxer->stream);
-        avio_flush(priv->avfc->pb);
         av_seek_frame(priv->avfc, 0, stream_tell(demuxer->stream),
                       AVSEEK_FLAG_BYTE);
-        avio_flush(priv->avfc->pb);
+        // avio_flush() is designed for write-only streams, and does the wrong
+        // thing when reading. Flush it manually instead.
+        priv->avfc->pb->buf_ptr = priv->avfc->pb->buf_end;
+        stream_drop_buffers(demuxer->stream);
         return DEMUXER_CTRL_OK;
     default:
         return DEMUXER_CTRL_NOTIMPL;