[FFmpeg-devel] [PATCH] au: add duration info

[Michael Niedermayer]

On Sun, Jul 17, 2011 at 03:14:33PM +0200, Stefano Sabatini wrote:
> On date Saturday 2011-07-16 17:36:55 +0200, Stefano Sabatini encoded:
> > On date Thursday 2011-07-14 12:06:17 +0200, ami_stuff encoded:
> > > Modified.
> > > 
> > > Regards
> > 
> > > diff --git a/libavformat/au.c b/libavformat/au.c
> > > index 23365c4..f361a71 100644
> > > --- a/libavformat/au.c
> > > +++ b/libavformat/au.c
> > > @@ -120,7 +120,7 @@ static int au_probe(AVProbeData *p)
> > >  static int au_read_header(AVFormatContext *s,
> > >                            AVFormatParameters *ap)
> > >  {
> > > -    int size;
> > > +    int size, data_size = 0;
> > >      unsigned int tag;
> > >      AVIOContext *pb = s->pb;
> > >      unsigned int id, channels, rate;
> > > @@ -132,7 +132,12 @@ static int au_read_header(AVFormatContext *s,
> > >      if (tag != MKTAG('.', 's', 'n', 'd'))
> > >          return -1;
> > >      size = avio_rb32(pb); /* header size */
> > > -    avio_rb32(pb); /* data size */
> > > +    data_size = avio_rb32(pb); /* size in bytes */
> > > +
> > > +    if (data_size < 0) {
> > > +        av_log(s, AV_LOG_ERROR, "negative data_size\n");
> > > +        return AVERROR_INVALIDDATA;
> > > +    }
> > >  
> > >      id = avio_rb32(pb);
> > >      rate = avio_rb32(pb);
> > > @@ -159,6 +164,10 @@ static int au_read_header(AVFormatContext *s,
> > >      st->codec->codec_id = codec;
> > >      st->codec->channels = channels;
> > >      st->codec->sample_rate = rate;
> > > +
> > > +    if (data_size)
> > > +        st->duration = (int64_t)(data_size) / (st->codec->channels * (uint64_t)(av_get_bits_per_sample(st->codec->codec_id)>>3));
> 
> Re-reading the comment from Michael, I realived this was not what he
> meant.
> 
> In case of coded samples, av_get_bits_per_sample(st->codec->codec_id)
> can be < 8 so if you shift by >>3 you get a 0 in the denominator.
> 
> Also data_size << 3 may overflow, but if you cast the int to a
> variable with a greater number of bits *before* to shift, then you're
> sure it won't.
> 
> So you can write it as:
> 
> if (data_size) // data size expressed in bits
>     st->duration = (((int64_t)data_size) << 3) / (st->codec->channels * (uint64_t)(av_get_bits_per_sample(st->codec->codec_id));
> 
> Also the "if (data_size)" check can be avoided since it will return
> the same value of 0 if the expression is evaluated.
> 
> BTW I'm not totally sure that the int -> int64_t cast is to be
> considered correct, e.g. it may happen that:
> sizeof(int64_t) == sizeof(int)
> in this case the two types have the same "numerability", (and in
> general it could be even happen that sizeof(int64_t) < sizeof(int),
> right?).

yes but whats read from the file is 32bit

> 
> So a possibly safer alternative would be to use floating point
> arithmetic:

with float you can end up with platform specific results.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you think the mosad wants you dead since a long time then you are either
wrong or dead since a long time.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20110718/095f6b3d/attachment.asc>