avformat/avidec: add mp2 to the list of exceptions instead of generally treating dshow_block_align==1 special

Fixes Ticket4552

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avidec.c

@@ -129,7 +129,7 @@ static inline int get_duration(AVIStream *ast, int len)
 {
     if (ast->sample_size)
         return len;
-    else if (ast->dshow_block_align > 1)
+    else if (ast->dshow_block_align)
         return (len + ast->dshow_block_align - 1) / ast->dshow_block_align;
     else
         return 1;
@@ -872,7 +872,8 @@ static int avi_read_header(AVFormatContext *s)
                         st->codec->codec_id    = AV_CODEC_ID_ADPCM_IMA_AMV;
                         ast->dshow_block_align = 0;
                     }
-                    if (st->codec->codec_id == AV_CODEC_ID_AAC && ast->dshow_block_align <= 4 && ast->dshow_block_align) {
+                    if (st->codec->codec_id == AV_CODEC_ID_AAC && ast->dshow_block_align <= 4 && ast->dshow_block_align ||
+                        st->codec->codec_id == AV_CODEC_ID_MP2 && ast->dshow_block_align <= 4 && ast->dshow_block_align) {
                         av_log(s, AV_LOG_DEBUG, "overriding invalid dshow_block_align of %d\n", ast->dshow_block_align);
                         ast->dshow_block_align = 0;
                     }