shithub: opusfile

Info  •  Files  •  Log  •  Branches

Use clipping prevention on 16-bit decode paths.

When we decode using libopus's fixed-point APIs, libopus internally
 applies soft clipping prevention.
When we decode using libopus's floating-point APIs, this behavior
 is disabled.
If we're ultimately planning to output the data to the user in
 fixed-point, we need to apply the clipping prevention ourselves.

--- a/src/internal.h

+++ b/src/internal.h

@@ -38,6 +38,13 @@

 typedef float      op_sample;

 # endif

+/*We're using this define to test for libopus 1.1 or later until libopus

+   provides a better mechanism.*/

+# if defined(OPUS_GET_EXPERT_FRAME_DURATION_REQUEST)

+/*Enable soft clipping prevention in 16-bit decodes.*/

+#  define OP_SOFT_CLIP (1)

+# endif

+

 # if OP_GNUC_PREREQ(4,2)

 /*Disable excessive warnings about the order of operations.*/

 #  pragma GCC diagnostic ignored "-Wparentheses"

@@ -203,8 +210,11 @@

   int                od_buffer_pos;

   /*The number of valid samples in the decoded buffer.*/

   int                od_buffer_size;

-  /*Internal state for dithering float->short output.*/

+  /*Internal state for soft clipping and dithering float->short output.*/

 #if !defined(OP_FIXED_POINT)

+# if defined(OP_SOFT_CLIP)

+  float              clip_state[OP_NCHANNELS_MAX];

+# endif

   float              dither_a[OP_NCHANNELS_MAX*4];

   float              dither_b[OP_NCHANNELS_MAX*4];

   int                dither_mute;

--- a/src/opusfile.c

+++ b/src/opusfile.c

@@ -2898,19 +2898,27 @@

 };

 static void op_shaped_dither16(OggOpusFile *_of,opus_int16 *_dst,

- const float *_src,int _nsamples,int _nchannels){

+ 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;

+  if(_of->state_channel_count!=_nchannels){

+    mute=65;

+# if defined(OP_SOFT_CLIP)

+    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;

-    int ci;

     silent=1;

     for(ci=0;ci<_nchannels;ci++){

       float r;