lavc/aac_ac3_parser: fix potential overflow when averaging bitrate

The new code is analog to how it's done in our mpegaudio parser.

Acked-by: Jun Zhao <barryjzhao@tencent.com>
Signed-off-by: Alexander Strasser <eclipse7@gmx.net>

2 files changed, 2 insertions, 4 deletions

diff --git a/libavcodec/aac_ac3_parser.c b/libavcodec/aac_ac3_parser.c
index 0746798dab..e5d4b53339 100644
--- a/libavcodec/aac_ac3_parser.c
+++ b/libavcodec/aac_ac3_parser.c
@@ -100,9 +100,8 @@ get_next:
         /* Calculate the average bit rate */
         s->frame_number++;
         if (avctx->codec_id != AV_CODEC_ID_EAC3) {
-            avctx->bit_rate =
-                (s->last_bit_rate * (s->frame_number -1) + s->bit_rate)/s->frame_number;
-            s->last_bit_rate = avctx->bit_rate;
+            avctx->bit_rate +=
+                (s->bit_rate - avctx->bit_rate) / s->frame_number;
         }
     }
 
diff --git a/libavcodec/aac_ac3_parser.h b/libavcodec/aac_ac3_parser.h
index b04041f69d..8b93cbf84f 100644
--- a/libavcodec/aac_ac3_parser.h
+++ b/libavcodec/aac_ac3_parser.h
@@ -56,7 +56,6 @@ typedef struct AACAC3ParseContext {
 
     int need_next_header;
     int frame_number;
-    int last_bit_rate;
     enum AVCodecID codec_id;
 } AACAC3ParseContext;