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

[Måns Rullgård]

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.

-- 
M?ns Rullg?rd
mans at mansr.com