diff --git a/ffmpeg.c b/ffmpeg.c
index ec9117ae5e..ab83b3e8c2 100644
--- a/ffmpeg.c
+++ b/ffmpeg.c
@@ -1677,6 +1677,8 @@ static int av_encode(AVFormatContext **output_files,
                 codec->block_align= icodec->block_align;
                 if(codec->block_align == 1 && codec->codec_id == CODEC_ID_MP3)
                     codec->block_align= 0;
+                if(codec->codec_id == CODEC_ID_AC3)
+                    codec->block_align= 0;
                 break;
             case CODEC_TYPE_VIDEO:
                 if(using_vhook) {