source/mp3decoder.cpp

   1 #include <limits>
   2 #include <mad.h>
   3 #include <msp/strings/format.h>
   4 #include "mp3decoder.h"
   5
   6 using namespace std;
   7
   8 namespace {
   9
  10 Msp::Int16 scale(mad_fixed_t sample)
  11 {
  12         if(sample<=-MAD_F_ONE)
  13                 return numeric_limits<Msp::Int16>::min();
  14         else if(sample>=MAD_F_ONE)
  15                 return numeric_limits<Msp::Int16>::max();
  16         else
  17                 return (sample + (1<<(MAD_F_FRACBITS-16))) >> (MAD_F_FRACBITS-15);
  18 }
  19
  20 } // namespace
  21
  22
  23 namespace Msp {
  24 namespace AL {
  25
  26 mp3_error::mp3_error(const std::string &func, int err):
  27         runtime_error(format("%s: %s", func, get_message(err)))
  28 { }
  29
  30 string mp3_error::get_message(int err)
  31 {
  32         return format("%d", err);
  33 }
  34
  35
  36 struct Mp3Decoder::Private
  37 {
  38         mad_stream stream;
  39         mad_frame frame;
  40         mad_synth synth;
  41 };
  42
  43
  44 Mp3Decoder::Mp3Decoder(IO::Seekable &io):
  45         priv(new Private),
  46         in(io),
  47         in_buf_size(16384),
  48         in_buffer(new char[in_buf_size]),
  49         read_pos(0)
  50 {
  51         mad_stream_init(&priv->stream);
  52         mad_frame_init(&priv->frame);
  53         mad_synth_init(&priv->synth);
  54
  55         try
  56         {
  57                 decode_frame();
  58                 format = (priv->frame.header.mode==MAD_MODE_SINGLE_CHANNEL ? MONO16 : STEREO16);
  59                 freq = priv->frame.header.samplerate;
  60         }
  61         catch(...)
  62         {
  63                 delete[] in_buffer;
  64                 throw;
  65         }
  66 }
  67
  68 Mp3Decoder::~Mp3Decoder()
  69 {
  70         delete[] in_buffer;
  71         mad_synth_finish(&priv->synth);
  72         mad_frame_finish(&priv->frame);
  73         mad_stream_finish(&priv->stream);
  74         delete priv;
  75 }
  76
  77 bool Mp3Decoder::detect(const string &sig)
  78 {
  79         if(sig.size()>=2 && sig[0]=='\xFF' && (sig[1]&0xE0)==0xE0)
  80                 return true;
  81
  82         static const char id3_sig[] = { 'I', 'D', '3' };
  83         if(sig.size()<sizeof(id3_sig))
  84                 return false;
  85         return !sig.compare(0, sizeof(id3_sig), id3_sig);
  86 }
  87
  88 void Mp3Decoder::rewind()
  89 {
  90         in.seek(0, IO::S_BEG);
  91 }
  92
  93 unsigned Mp3Decoder::read(char *buf, unsigned len)
  94 {
  95         unsigned nchan = (format==STEREO16 ? 2 : 1);
  96         mad_pcm &pcm = priv->synth.pcm;
  97
  98         unsigned pos = 0;
  99         while(pos+2*nchan<=len)
 100         {
 101                 if(read_pos>=pcm.length)
 102                 {
 103                         if(!decode_frame())
 104                                 break;
 105                 }
 106
 107                 for(unsigned i=0; i<nchan; ++i)
 108                 {
 109                         Int16 sample = scale(pcm.samples[i][read_pos]);
 110                         buf[pos++] = sample;
 111                         buf[pos++] = sample>>8;
 112                 }
 113
 114                 ++read_pos;
 115         }
 116
 117         return pos;
 118 }
 119
 120 bool Mp3Decoder::fill_input()
 121 {
 122         unsigned in_pos = 0;
 123         if(priv->stream.next_frame && priv->stream.next_frame<priv->stream.bufend)
 124         {
 125                 copy(priv->stream.next_frame, priv->stream.bufend, in_buffer);
 126                 in_pos = priv->stream.bufend-priv->stream.next_frame;
 127         }
 128
 129         unsigned len = in.read(in_buffer+in_pos, in_buf_size-in_pos);
 130         in_pos += len;
 131
 132         mad_stream_buffer(&priv->stream, reinterpret_cast<unsigned char *>(in_buffer), in_pos);
 133         priv->stream.error = MAD_ERROR_NONE;
 134
 135         return len;
 136 }
 137
 138 bool Mp3Decoder::decode_frame()
 139 {
 140         while(1)
 141         {
 142                 if(!priv->stream.buffer || priv->stream.error==MAD_ERROR_BUFLEN)
 143                         if(!fill_input())
 144                                 return false;
 145
 146                 if(!mad_frame_decode(&priv->frame, &priv->stream))
 147                 {
 148                         mad_synth_frame(&priv->synth, &priv->frame);
 149                         read_pos = 0;
 150                         return true;
 151                 }
 152
 153                 if(priv->stream.error==MAD_ERROR_BUFLEN)
 154                         continue;
 155                 else if(!MAD_RECOVERABLE(priv->stream.error))
 156                         throw mp3_error("mad_frame_decode", priv->stream.error);
 157         }
 158 }
 159
 160 } // namespace AL
 161 } // namespace Msp