[FFmpeg-devel] [PATCH] add (e)ac3float decoders

[Michael Niedermayer]

On Thu, Mar 10, 2011 at 02:52:15PM +0000, M?ns Rullg?rd wrote:
> FB2000 <flybird2k at gmail.com> writes:
> 
> > On Tue, Mar 8, 2011 at 5:27 AM, Michael Niedermayer <michaelni at gmx.at>
> > wrote:
> >
> >> On Mon, Mar 07, 2011 at 03:01:46PM -0500, Justin Ruggles wrote:
> >> >
> >> > 1) There is no need for separate int16 and float decoders. The AC3
> >> > decoder is a floating-point decoder. It just happens to output int16 at
> >> > the end.
> >>
> >> can you send a patch that does this?
> >>
> >>
> > Well, if these are what wanted. See attached patches for AC3 and DCA.
> >
> > FB2000
> >
> > diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
> > index 5ebee19..882e1c5 100644
> > --- a/libavcodec/ac3dec.c
> > +++ b/libavcodec/ac3dec.c
> > @@ -196,8 +196,7 @@ static av_cold int ac3_decode_init(AVCodecContext *avctx)
> >      ff_fmt_convert_init(&s->fmt_conv, avctx);
> >      av_lfg_init(&s->dith_state, 0);
> >  
> > -    /* set scale value for float to int16 conversion */
> > -    s->mul_bias = 32767.0f;
> > +    s->mul_bias = 1.0f;
> >  
> >      /* allow downmixing to stereo or mono */
> >      if (avctx->channels > 0 && avctx->request_channels > 0 &&
> > @@ -214,7 +213,7 @@ static av_cold int ac3_decode_init(AVCodecContext *avctx)
> >              return AVERROR(ENOMEM);
> >      }
> >  
> > -    avctx->sample_fmt = AV_SAMPLE_FMT_S16;
> > +    avctx->sample_fmt = AV_SAMPLE_FMT_FLT;
> >      return 0;
> >  }
> >  
> > @@ -1308,8 +1307,8 @@ static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size,
> >      const uint8_t *buf = avpkt->data;
> >      int buf_size = avpkt->size;
> >      AC3DecodeContext *s = avctx->priv_data;
> > -    int16_t *out_samples = (int16_t *)data;
> > -    int blk, ch, err;
> > +    float *out_samples = (float *)data;
> > +    int i, blk, ch, err;
> >      const uint8_t *channel_map;
> >      const float *output[AC3_MAX_CHANNELS];
> >  
> > @@ -1408,10 +1407,11 @@ static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size,
> >              av_log(avctx, AV_LOG_ERROR, "error decoding the audio block\n");
> >              err = 1;
> >          }
> > -        s->fmt_conv.float_to_int16_interleave(out_samples, output, 256, s->out_channels);
> > -        out_samples += 256 * s->out_channels;
> > +        for (i = 0; i < 256; i++)
> > +            for (ch = 0; ch < s->out_channels; ch++)
> > +                *(out_samples++) = output[ch][i];
> >      }
> > -    *data_size = s->num_blocks * 256 * avctx->channels * sizeof (int16_t);
> > +    *data_size = s->num_blocks * 256 * avctx->channels * sizeof (float);
> >      return FFMIN(buf_size, s->frame_size);
> >  }
> 
> This gives a 5x slowdown on ARM.  That is unacceptable.

you need 5 times more time to do the same thing outside the codec as inside?

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

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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