[FFmpeg-devel] [PATCH]Ignore xing number of frames if filesize is wrong

[Carl Eugen Hoyos]

On Thursday 17 July 2014 09:41:40 pm Nicolas George wrote:
> Le nonidi 29 messidor, an CCXXII, Carl Eugen Hoyos a écrit :
> >
> > Attached patch fixes ticket #3777 for me, analyzed by Oliver 
> > Fromme. 

> I would suggest to avoid floating point arithmetic if possible. 
> Possibly something like that:
>
> uint64_t min = FFMIN(fsize, mp3->header_filesize);
> uint64_t delta = FFMAX(fsize, mp3->header_filesize) - min;
> uint64_t tolerance = min / 20;
> if (... && min - tolerance < 2 * tolerance)
>
> I also find this version easier to understand.

Thank you, new patch attached.

> I can not judge on the correctness, though.

The logic is copied from asfdec.c.

Please review, Carl Eugen
-------------- next part --------------
diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
index 8335388..cf5aa73 100644
--- a/libavformat/mp3dec.c
+++ b/libavformat/mp3dec.c
@@ -138,6 +138,7 @@ static void mp3_parse_info_tag(AVFormatContext *s, AVStream *st,
 
     MP3DecContext *mp3 = s->priv_data;
     static const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
+    uint64_t min, delta, fsize = avio_size(s->pb);
 
     /* Check for Xing / Info tag */
     avio_skip(s->pb, xing_offtbl[c->lsf == 1][c->nb_channels == 1]);
@@ -151,6 +152,10 @@ static void mp3_parse_info_tag(AVFormatContext *s, AVStream *st,
         mp3->frames = avio_rb32(s->pb);
     if (v & XING_FLAG_SIZE)
         mp3->header_filesize = avio_rb32(s->pb);
+    min = FFMIN(fsize, mp3->header_filesize);
+    delta = FFMAX(fsize, mp3->header_filesize) - min;
+    if (fsize && mp3->header_filesize > 0 && delta > min >> 4)
+        mp3->frames = 0;
     if (v & XING_FLAG_TOC)
         read_xing_toc(s, mp3->header_filesize, av_rescale_q(mp3->frames,
                                        (AVRational){spf, c->sample_rate},