[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 :
> > Hi!
> >
> > Attached patch fixes ticket #3777 for me, analyzed by Oliver Fromme.
> >
> > Please comment, Carl Eugen
> >
> > diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
> > index 8335388..cdef6d9 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}};
> > +    int64_t 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 +152,9 @@ 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);
> >
> > +    if (fsize > 0 && mp3->header_filesize > 0 &&
> > +        FFABS(fsize - (int64_t)mp3->header_filesize) /
> > (float)FFMIN(fsize, mp3->header_filesize) > 0.05)
>
> 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.
>
> And in any case, someone may correct me, but I believe nowadays double
> should always preferred to float unless you need a lot of them and want to
> reduce the memory use.
>
> I can not judge on the correctness, though.
>
> > +        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},
>
> Regards,