[FFmpeg-devel] [HOWTO] Building FFmpeg for iPhone

[Reimar Döffinger]

On Thu, Oct 08, 2009 at 12:03:57PM +0100, M?ns Rullg?rd wrote:
> David Conrad <lessen42 at gmail.com> writes:
> 
> > On Oct 7, 2009, at 10:07 AM, Jason Millard wrote:
> >
> >> --arch=arm --extra-cflags='-arch armv6' --extra-ldflags='-arch armv6'
> >> Thanks. that did the trick. With my tests, mp3 decoding is fine, but
> >> aac
> >> decoding is mostly static -- (almost like the volume is amplified)
> >
> > Reproduced, it's because the aac and dca decoders check for the C
> > version of float_to_int16 but use float_to_int16_interleave, which
> > doesn't have a VFP version.
> >
> > Patch attached
> >
> >
> > commit 2f891fb5b0097b000303e0ee4d085a492dbc7fed
> > Author: David Conrad <lessen42 at gmail.com>
> > Date:   Thu Oct 8 06:50:21 2009 -0400
> >
> >     dca and aac decoders use float_to_int16_interleave, so check for
> >     the C version of that rather than float_to_int16.
> >     Fixes output on ARM/VFP
> >
> > diff --git a/libavcodec/aac.c b/libavcodec/aac.c
> > index 2dc7960..68a007b 100644
> > --- a/libavcodec/aac.c
> > +++ b/libavcodec/aac.c
> > @@ -527,7 +527,7 @@ static av_cold int aac_decode_init(AVCodecContext *avccontext)
> >      // 32768 - Required to scale values to the correct range for the bias method
> >      //         for float to int16 conversion.
> >
> > -    if (ac->dsp.float_to_int16 == ff_float_to_int16_c) {
> > +    if (ac->dsp.float_to_int16_interleave == ff_float_to_int16_interleave_c) {
> >          ac->add_bias  = 385.0f;
> >          ac->sf_scale  = 1. / (-1024. * 32768.);
> >          ac->sf_offset = 0;
> > diff --git a/libavcodec/dca.c b/libavcodec/dca.c
> > index b68e547..e411c36 100644
> > --- a/libavcodec/dca.c
> > +++ b/libavcodec/dca.c
> > @@ -1324,7 +1324,7 @@ static av_cold int dca_decode_init(AVCodecContext * avctx)
> >          s->samples_chanptr[i] = s->samples + i * 256;
> >      avctx->sample_fmt = SAMPLE_FMT_S16;
> >
> > -    if(s->dsp.float_to_int16 == ff_float_to_int16_c) {
> > +    if(s->dsp.float_to_int16_interleave == ff_float_to_int16_interleave_c) {
> >          s->add_bias = 385.0f;
> >          s->scale_bias = 1.0 / 32768.0;
> >      } else {
> 
> The idea of checking those functions like that is dreadful, but this
> doesn't make it any worse, and it does fix a bug.  I say apply.

Maybe those values (385.0f, 1.0 / 32768.0) should just be added to the DspContext?
Of course that depends on what sf_offset is and what its meaning is...