ref: 8396a1f85c540937b4b828b1465d34b9be806ce9
parent: a88a90f9ab476d2629ec5999a34ce5eb76a73a61
author: Timothy B. Terriberry <tterribe@xiph.org>
date: Wed Aug 28 20:36:13 EDT 2013
Add an API to disable dithering. This is to correspond to the feature in opus-tools's opusdec. opusdec itself probably won't be able to use it, because it still wants to do dithering after resampling, but the motivation for the feature is the same.
--- a/include/opusfile.h
+++ b/include/opusfile.h
@@ -1777,6 +1777,18 @@
int op_set_gain_offset(OggOpusFile *_of,
int _gain_type,opus_int32 _gain_offset_q8) OP_ARG_NONNULL(1);
+/**Sets whether or not dithering is enabled for 16-bit decoding.
+ By default, when <tt>libopusfile</tt> is compiled to use floating-point
+ internally, calling op_read() or op_read_stereo() will first decode to
+ float, and then convert to fixed-point using noise-shaping dithering.
+ This flag can be used to disable that dithering.
+ When the application uses op_read_float() or op_read_float_stereo(), or when
+ the library has been compiled to decode directly to fixed point, this flag
+ has no effect.
+ \param _of The \c OggOpusFile on which to enable or disable dithering.
+ \param _enabled A non-zero value to enable dithering, or 0 to disable it.*/
+void op_set_dither_enabled(OggOpusFile *_of,int _enabled) OP_ARG_NONNULL(1);
+
/**Reads more samples from the stream.
\note Although \a _buf_size must indicate the total number of values that
can be stored in \a _pcm, the return value is the number of samples
--- a/src/internal.h
+++ b/src/internal.h
@@ -235,6 +235,7 @@
float dither_b[OP_NCHANNELS_MAX*4];
opus_uint32 dither_seed;
int dither_mute;
+ int dither_disabled;
/*The number of channels represented by the internal state.
This gets set to 0 whenever anything that would prevent state propagation
occurs (switching between the float/short APIs, or between the
--- a/src/opusfile.c
+++ b/src/opusfile.c
@@ -2566,6 +2566,13 @@
return 0;
}
+void op_set_dither_enabled(OggOpusFile *_of,int _enabled){+#if !defined(OP_FIXED_POINT)
+ _of->dither_disabled=!_enabled;
+ if(!_enabled)_of->dither_mute=65;
+#endif
+}
+
/*Allocate the decoder scratch buffer.
This is done lazily, since if the user provides large enough buffers, we'll
never need it.*/
@@ -3000,69 +3007,74 @@
static void op_shaped_dither16(OggOpusFile *_of,opus_int16 *_dst,
float *_src,int _nsamples,int _nchannels){- opus_uint32 seed;
- int mute;
- int ci;
- int i;
- mute=_of->dither_mute;
- seed=_of->dither_seed;
- if(_of->state_channel_count!=_nchannels){- mute=65;
+ int ci;
+ int i;
# if defined(OP_SOFT_CLIP)
+ if(_of->state_channel_count!=_nchannels){for(ci=0;ci<_nchannels;ci++)_of->clip_state[ci]=0;
-# endif
}
-# if defined(OP_SOFT_CLIP)
opus_pcm_soft_clip(_src,_nsamples,_nchannels,_of->clip_state);
# endif
- /*In order to avoid replacing digital silence with quiet dither noise, we
- mute if the output has been silent for a while.*/
- if(mute>64)memset(_of->dither_a,0,sizeof(*_of->dither_a)*4*_nchannels);
- for(i=0;i<_nsamples;i++){- int silent;
- silent=1;
- for(ci=0;ci<_nchannels;ci++){- float r;
- float s;
- float err;
- int si;
- int j;
- s=_src[_nchannels*i+ci];
- silent&=s==0;
- s*=OP_GAIN;
- err=0;
- for(j=0;j<4;j++){- err+=OP_FCOEF_B[j]*_of->dither_b[ci*4+j]
- -OP_FCOEF_A[j]*_of->dither_a[ci*4+j];
+ if(_of->dither_disabled){+ for(i=0;i<_nchannels*_nsamples;i++){+ _dst[i]=op_float2int(OP_CLAMP(-32768,32768.0F*_src[i],32767));
+ }
+ }
+ else{+ opus_uint32 seed;
+ int mute;
+ seed=_of->dither_seed;
+ mute=_of->dither_mute;
+ if(_of->state_channel_count!=_nchannels)mute=65;
+ /*In order to avoid replacing digital silence with quiet dither noise, we
+ mute if the output has been silent for a while.*/
+ if(mute>64)memset(_of->dither_a,0,sizeof(*_of->dither_a)*4*_nchannels);
+ for(i=0;i<_nsamples;i++){+ int silent;
+ silent=1;
+ for(ci=0;ci<_nchannels;ci++){+ float r;
+ float s;
+ float err;
+ int si;
+ int j;
+ s=_src[_nchannels*i+ci];
+ silent&=s==0;
+ s*=OP_GAIN;
+ err=0;
+ for(j=0;j<4;j++){+ err+=OP_FCOEF_B[j]*_of->dither_b[ci*4+j]
+ -OP_FCOEF_A[j]*_of->dither_a[ci*4+j];
+ }
+ for(j=3;j-->0;)_of->dither_a[ci*4+j+1]=_of->dither_a[ci*4+j];
+ for(j=3;j-->0;)_of->dither_b[ci*4+j+1]=_of->dither_b[ci*4+j];
+ _of->dither_a[ci*4]=err;
+ s-=err;
+ if(mute>16)r=0;
+ else{+ seed=op_rand(seed);
+ r=seed*OP_PRNG_GAIN;
+ seed=op_rand(seed);
+ r-=seed*OP_PRNG_GAIN;
+ }
+ /*Clamp in float out of paranoia that the input will be > 96 dBFS and
+ wrap if the integer is clamped.*/
+ si=op_float2int(OP_CLAMP(-32768,s+r,32767));
+ _dst[_nchannels*i+ci]=(opus_int16)si;
+ /*Including clipping in the noise shaping is generally disastrous: the
+ futile effort to restore the clipped energy results in more clipping.
+ However, small amounts---at the level which could normally be created
+ by dither and rounding---are harmless and can even reduce clipping
+ somewhat due to the clipping sometimes reducing the dither + rounding
+ error.*/
+ _of->dither_b[ci*4]=mute>16?0:OP_CLAMP(-1.5F,si-s,1.5F);
}
- for(j=3;j-->0;)_of->dither_a[ci*4+j+1]=_of->dither_a[ci*4+j];
- for(j=3;j-->0;)_of->dither_b[ci*4+j+1]=_of->dither_b[ci*4+j];
- _of->dither_a[ci*4]=err;
- s-=err;
- if(mute>16)r=0;
- else{- seed=op_rand(seed);
- r=seed*OP_PRNG_GAIN;
- seed=op_rand(seed);
- r-=seed*OP_PRNG_GAIN;
- }
- /*Clamp in float out of paranoia that the input will be > 96 dBFS and
- wrap if the integer is clamped.*/
- si=op_float2int(OP_CLAMP(-32768,s+r,32767));
- _dst[_nchannels*i+ci]=(opus_int16)si;
- /*Including clipping in the noise shaping is generally disastrous: the
- futile effort to restore the clipped energy results in more clipping.
- However, small amounts---at the level which could normally be created
- by dither and rounding---are harmless and can even reduce clipping
- somewhat due to the clipping sometimes reducing the dither + rounding
- error.*/
- _of->dither_b[ci*4]=mute>16?0:OP_CLAMP(-1.5F,si-s,1.5F);
+ mute++;
+ if(!silent)mute=0;
}
- mute++;
- if(!silent)mute=0;
+ _of->dither_mute=OP_MIN(mute,65);
+ _of->dither_seed=seed;
}
- _of->dither_mute=OP_MIN(mute,65);
- _of->dither_seed=seed;
_of->state_channel_count=_nchannels;
}