[FFmpeg-devel] [PATCH] Issue 636 : ALAC encoding sometimes fails

[Michael Niedermayer]

On Wed, Dec 10, 2008 at 10:49:10AM +0530, Jai Menon wrote:
> Hi,
> 
> -------- Original-Nachricht --------
> > Datum: Fri, 5 Dec 2008 13:16:59 +0100
> > Von: Michael Niedermayer <michaelni at gmx.at<http://service.gmx.net/de/cgi/g.fcgi/mail/new?CUSTOMERNO=12720674&t=uk602561993.1228886151.33ee9c8f&to=michaelni%40gmx.at>
> >
> > An: FFmpeg development discussions and patches <ffmpeg-devel at mplayerhq.hu<http://service.gmx.net/de/cgi/g.fcgi/mail/new?CUSTOMERNO=12720674&t=uk602561993.1228886151.33ee9c8f&to=ffmpeg-devel%40mplayerhq.hu>
> >
> > Betreff: Re: [FFmpeg-devel] [PATCH] Issue 636 : ALAC encoding
> sometimes    fails
> 
> > On Fri, Dec 05, 2008 at 10:09:16AM +0530, Jai Menon wrote:
> > > Hi,
> > >
> > > Attached patch fixes issue 636 and a few other fringe cases where the
> > > alac encoder produces
> > > lossy output. I'm behind a NAT and svn doesn't work, so could someone
> > > please apply. Thanks.
> > >
> > > Regards,
> > >
> > > Jai
> >
> > > Index: libavcodec/alacenc.c
> > > ===================================================================
> > > --- libavcodec/alacenc.c    (revision 15797)
> > > +++ libavcodec/alacenc.c    (working copy)
> > > @@<http://service.gmx.net/de/cgi/g.fcgi/mail/new?CUSTOMERNO=12720674&t=uk602561993.1228886151.33ee9c8f&to=>-253,7 +253,8
> @@<http://service.gmx.net/de/cgi/g.fcgi/mail/new?CUSTOMERNO=12720674&t=uk602561993.1228886151.33ee9c8f&to=>
> > >
> > >              sum >>= lpc.lpc_quant;
> > >              sum += samples[0];
> > > -            residual[i] = samples[lpc.lpc_order+1] - sum;
> > > +            residual[i] = (samples[lpc.lpc_order+1] - sum) << (32 -
> > s->write_sample_size) >>
> > > +                          (32 - s->write_sample_size);
> > >              res_val = residual[i];
> >
> > you are missing a int32_t cast in there, without it this wont work on
> > systems where int is not exactly 32bit
> >
> 
> Oversight on my part. 16 bit systems are a nightmare from which I'm trying
> to awake.

int could be 64bit, it cannot be 16bit on a POSIX system as its required
by POSIX to be >= 32


[...]

> @@ -253,7 +253,7 @@
>  
>              sum >>= lpc.lpc_quant;
>              sum += samples[0];
> -            residual[i] = (samples[lpc.lpc_order+1] - sum) << (32 - s->write_sample_size) >>
> +            residual[i] = (int32_t)(samples[lpc.lpc_order+1] - sum) << (32 - s->write_sample_size) >>
>                            (32 - s->write_sample_size);

id do the cast after the << because its the >> that differes from where
the sign bit is 

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

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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