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Adding a playback gain field to the header

--- a/src/opus_header.c

+++ b/src/opus_header.c

@@ -8,7 +8,8 @@

   - Channels C (8 bits)

   - Pre-skip (16 bits)

   - Sampling rate (32 bits)

-  - mapping (8bits, 0=single stream (mono/stereo) 1=Vorbis mapping, 

+  - Gain in dB (16 bits, S7.8)

+  - Mapping (8 bits, 0=single stream (mono/stereo) 1=Vorbis mapping, 

              2..254: reserved, 255: multistream with no mapping)

   - if (mapping != 0)

@@ -133,7 +134,11 @@

    if (!read_uint32(&p, &h->input_sample_rate))

       return 0;

-   

+

+   if (!read_uint16(&p, &shortval))

+      return 0;

+   h->gain = (short)shortval;

+

    if (!read_chars(&p, &ch, 1))

       return 0;

    h->channel_mapping = ch;

@@ -184,6 +189,9 @@

       return 0;

    if (!write_uint32(&p, h->input_sample_rate))

+      return 0;

+

+   if (!write_uint16(&p, h->gain))

       return 0;

    ch = h->channel_mapping;

--- a/src/opus_header.h

+++ b/src/opus_header.h

@@ -8,6 +8,7 @@

    int channels; /* Number of channels: 1..255 */

    int preskip;

    opus_uint32 input_sample_rate;

+   int gain; /* in dB S7.8 should be zero whenever possible */

    int channel_mapping;

    /* The rest is only used if channel_mapping != 0 */

    int nb_streams;

--- a/src/opusdec.c

+++ b/src/opusdec.c

@@ -292,7 +292,7 @@

    printf ("Copyright (C) 2008-2011 Jean-Marc Valin\n");

 }

-static OpusDecoder *process_header(ogg_packet *op, opus_int32 *rate, int *channels, int *preskip, int quiet)

+static OpusDecoder *process_header(ogg_packet *op, opus_int32 *rate, int *channels, int *preskip, float *gain, int quiet)

 {

    OpusDecoder *st;

    OpusHeader header;

@@ -321,6 +321,10 @@

       return NULL;

    }

+   *gain = pow(20., header.gain/2560.);

+

+   if (header.gain!=0)

+      printf("Playback gain: %f (%f dB)\n", *gain, header.gain/256.);

    if (!quiet)

    {

       fprintf (stderr, "Decoding %d Hz audio in", *rate);

@@ -413,7 +417,8 @@

    int preskip=0;

    int opus_serialno = -1;

    SpeexResamplerState *resampler=NULL;

-

+   float gain=1;

+   

    enh_enabled = 1;

    /*Process options*/

@@ -547,7 +552,7 @@

             /*If first packet, process as OPUS header*/

             if (packet_count==0)

             {

-               st = process_header(&op, &rate, &channels, &preskip, quiet);

+               st = process_header(&op, &rate, &channels, &preskip, &gain, quiet);

                /* Converting preskip to output sampling rate */

                preskip = preskip*(rate/48000.);

                if (!st)

@@ -593,6 +598,13 @@

                      break;

                   }

                   frame_size = ret;

+                  /* Apply header gain */

+                  for (i=0;i<frame_size*channels;i++)

+                  {

+                     float tmp = gain*output[i];

+                     tmp = (tmp < -32767) ? -32767 : ((tmp > 32767) ? 32767 : tmp);

+                     output[i] = floor(.5+tmp);

+                  }

                   if (print_bitrate) {

                      opus_int32 tmp=op.bytes;

                      char ch=13;

--- a/src/opusenc.c

+++ b/src/opusenc.c

@@ -509,6 +509,8 @@

    header.channel_mapping = 0;

    header.nb_streams = 1;

    header.nb_coupled = 1;

+   /* 0 dB gain is the recommended unless you know what you're doing */

+   header.gain = 0;

    header.input_sample_rate = rate;

    /* Extra samples that need to be read to compensate for the pre-skip */