music_mad.c
author Sam Lantinga <slouken@libsdl.org>
Sat, 02 Jan 2016 22:12:31 -0800
changeset 712 7e59d684b070
parent 711 f40c5ac95b12
child 725 bdf7b8d20566
permissions -rw-r--r--
Updated to version 2.0.1
     1 /*
     2   SDL_mixer:  An audio mixer library based on the SDL library
     3   Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 */
    21 
    22 #ifdef MP3_MAD_MUSIC
    23 
    24 #include <string.h>
    25 
    26 #include "music_mad.h"
    27 
    28 mad_data *
    29 mad_openFileRW(SDL_RWops *src, SDL_AudioSpec *mixer, int freesrc)
    30 {
    31   mad_data *mp3_mad;
    32 
    33   mp3_mad = (mad_data *)SDL_malloc(sizeof(mad_data));
    34   if (mp3_mad) {
    35     mp3_mad->src = src;
    36     mp3_mad->freesrc = freesrc;
    37     mad_stream_init(&mp3_mad->stream);
    38     mad_frame_init(&mp3_mad->frame);
    39     mad_synth_init(&mp3_mad->synth);
    40     mp3_mad->frames_read = 0;
    41     mad_timer_reset(&mp3_mad->next_frame_start);
    42     mp3_mad->volume = MIX_MAX_VOLUME;
    43     mp3_mad->status = 0;
    44     mp3_mad->output_begin = 0;
    45     mp3_mad->output_end = 0;
    46     mp3_mad->mixer = *mixer;
    47   }
    48   return mp3_mad;
    49 }
    50 
    51 void
    52 mad_closeFile(mad_data *mp3_mad)
    53 {
    54   mad_stream_finish(&mp3_mad->stream);
    55   mad_frame_finish(&mp3_mad->frame);
    56   mad_synth_finish(&mp3_mad->synth);
    57 
    58   if (mp3_mad->freesrc) {
    59     SDL_RWclose(mp3_mad->src);
    60   }
    61   SDL_free(mp3_mad);
    62 }
    63 
    64 /* Starts the playback. */
    65 void
    66 mad_start(mad_data *mp3_mad) {
    67   mp3_mad->status |= MS_playing;
    68 }
    69 
    70 /* Stops the playback. */
    71 void
    72 mad_stop(mad_data *mp3_mad) {
    73   mp3_mad->status &= ~MS_playing;
    74 }
    75 
    76 /* Returns true if the playing is engaged, false otherwise. */
    77 int
    78 mad_isPlaying(mad_data *mp3_mad) {
    79   return ((mp3_mad->status & MS_playing) != 0);
    80 }
    81 
    82 /* Reads the next frame from the file.  Returns true on success or
    83    false on failure. */
    84 static int
    85 read_next_frame(mad_data *mp3_mad) {
    86   if (mp3_mad->stream.buffer == NULL ||
    87       mp3_mad->stream.error == MAD_ERROR_BUFLEN) {
    88     size_t read_size;
    89     size_t remaining;
    90     unsigned char *read_start;
    91 
    92     /* There might be some bytes in the buffer left over from last
    93        time.  If so, move them down and read more bytes following
    94        them. */
    95     if (mp3_mad->stream.next_frame != NULL) {
    96       remaining = mp3_mad->stream.bufend - mp3_mad->stream.next_frame;
    97       memmove(mp3_mad->input_buffer, mp3_mad->stream.next_frame, remaining);
    98       read_start = mp3_mad->input_buffer + remaining;
    99       read_size = MAD_INPUT_BUFFER_SIZE - remaining;
   100 
   101     } else {
   102       read_size = MAD_INPUT_BUFFER_SIZE;
   103       read_start = mp3_mad->input_buffer;
   104       remaining = 0;
   105     }
   106 
   107     /* Now read additional bytes from the input file. */
   108     read_size = SDL_RWread(mp3_mad->src, read_start, 1, read_size);
   109 
   110     if (read_size <= 0) {
   111       if ((mp3_mad->status & (MS_input_eof | MS_input_error)) == 0) {
   112         if (read_size == 0) {
   113           mp3_mad->status |= MS_input_eof;
   114         } else {
   115           mp3_mad->status |= MS_input_error;
   116         }
   117 
   118         /* At the end of the file, we must stuff MAD_BUFFER_GUARD
   119            number of 0 bytes. */
   120         SDL_memset(read_start + read_size, 0, MAD_BUFFER_GUARD);
   121         read_size += MAD_BUFFER_GUARD;
   122       }
   123     }
   124 
   125     /* Now feed those bytes into the libmad stream. */
   126     mad_stream_buffer(&mp3_mad->stream, mp3_mad->input_buffer,
   127                       read_size + remaining);
   128     mp3_mad->stream.error = MAD_ERROR_NONE;
   129   }
   130 
   131   /* Now ask libmad to extract a frame from the data we just put in
   132      its buffer. */
   133   if (mad_frame_decode(&mp3_mad->frame, &mp3_mad->stream)) {
   134     if (MAD_RECOVERABLE(mp3_mad->stream.error)) {
   135       return 0;
   136 
   137     } else if (mp3_mad->stream.error == MAD_ERROR_BUFLEN) {
   138       return 0;
   139 
   140     } else {
   141       mp3_mad->status |= MS_decode_error;
   142       return 0;
   143     }
   144   }
   145 
   146   mp3_mad->frames_read++;
   147   mad_timer_add(&mp3_mad->next_frame_start, mp3_mad->frame.header.duration);
   148 
   149   return 1;
   150 }
   151 
   152 /* Scale a MAD sample to 16 bits for output. */
   153 static signed int
   154 scale(mad_fixed_t sample) {
   155   /* round */
   156   sample += (1L << (MAD_F_FRACBITS - 16));
   157 
   158   /* clip */
   159   if (sample >= MAD_F_ONE)
   160     sample = MAD_F_ONE - 1;
   161   else if (sample < -MAD_F_ONE)
   162     sample = -MAD_F_ONE;
   163 
   164   /* quantize */
   165   return sample >> (MAD_F_FRACBITS + 1 - 16);
   166 }
   167 
   168 /* Once the frame has been read, copies its samples into the output
   169    buffer. */
   170 static void
   171 decode_frame(mad_data *mp3_mad) {
   172   struct mad_pcm *pcm;
   173   unsigned int nchannels, nsamples;
   174   mad_fixed_t const *left_ch, *right_ch;
   175   unsigned char *out;
   176   int ret;
   177 
   178   mad_synth_frame(&mp3_mad->synth, &mp3_mad->frame);
   179   pcm = &mp3_mad->synth.pcm;
   180   out = mp3_mad->output_buffer + mp3_mad->output_end;
   181 
   182   if ((mp3_mad->status & MS_cvt_decoded) == 0) {
   183     mp3_mad->status |= MS_cvt_decoded;
   184 
   185     /* The first frame determines some key properties of the stream.
   186        In particular, it tells us enough to set up the convert
   187        structure now. */
   188     SDL_BuildAudioCVT(&mp3_mad->cvt, AUDIO_S16, pcm->channels, mp3_mad->frame.header.samplerate, mp3_mad->mixer.format, mp3_mad->mixer.channels, mp3_mad->mixer.freq);
   189   }
   190 
   191   /* pcm->samplerate contains the sampling frequency */
   192 
   193   nchannels = pcm->channels;
   194   nsamples  = pcm->length;
   195   left_ch   = pcm->samples[0];
   196   right_ch  = pcm->samples[1];
   197 
   198   while (nsamples--) {
   199     signed int sample;
   200 
   201     /* output sample(s) in 16-bit signed little-endian PCM */
   202 
   203     sample = scale(*left_ch++);
   204     *out++ = ((sample >> 0) & 0xff);
   205     *out++ = ((sample >> 8) & 0xff);
   206 
   207     if (nchannels == 2) {
   208       sample = scale(*right_ch++);
   209       *out++ = ((sample >> 0) & 0xff);
   210       *out++ = ((sample >> 8) & 0xff);
   211     }
   212   }
   213 
   214   mp3_mad->output_end = out - mp3_mad->output_buffer;
   215   /*assert(mp3_mad->output_end <= MAD_OUTPUT_BUFFER_SIZE);*/
   216 }
   217 
   218 int
   219 mad_getSamples(mad_data *mp3_mad, Uint8 *stream, int len) {
   220   int bytes_remaining;
   221   int num_bytes;
   222   Uint8 *out;
   223 
   224   if ((mp3_mad->status & MS_playing) == 0) {
   225     /* We're not supposed to be playing, so send silence instead. */
   226     SDL_memset(stream, 0, len);
   227     return 0;
   228   }
   229 
   230   out = stream;
   231   bytes_remaining = len;
   232   while (bytes_remaining > 0) {
   233     if (mp3_mad->output_end == mp3_mad->output_begin) {
   234       /* We need to get a new frame. */
   235       mp3_mad->output_begin = 0;
   236       mp3_mad->output_end = 0;
   237       if (!read_next_frame(mp3_mad)) {
   238         if ((mp3_mad->status & MS_error_flags) != 0) {
   239           /* Couldn't read a frame; either an error condition or
   240              end-of-file.  Stop. */
   241           SDL_memset(out, 0, bytes_remaining);
   242           mp3_mad->status &= ~MS_playing;
   243           return bytes_remaining;
   244         }
   245       } else {
   246         decode_frame(mp3_mad);
   247 
   248         /* Now convert the frame data to the appropriate format for
   249            output. */
   250         mp3_mad->cvt.buf = mp3_mad->output_buffer;
   251         mp3_mad->cvt.len = mp3_mad->output_end;
   252 
   253         mp3_mad->output_end = (int)(mp3_mad->output_end * mp3_mad->cvt.len_ratio);
   254         /*assert(mp3_mad->output_end <= MAD_OUTPUT_BUFFER_SIZE);*/
   255         SDL_ConvertAudio(&mp3_mad->cvt);
   256       }
   257     }
   258 
   259     num_bytes = mp3_mad->output_end - mp3_mad->output_begin;
   260     if (bytes_remaining < num_bytes) {
   261       num_bytes = bytes_remaining;
   262     }
   263 
   264     if (mp3_mad->volume == MIX_MAX_VOLUME) {
   265       SDL_memcpy(out, mp3_mad->output_buffer + mp3_mad->output_begin, num_bytes);
   266     } else {
   267       SDL_MixAudio(out, mp3_mad->output_buffer + mp3_mad->output_begin,
   268                    num_bytes, mp3_mad->volume);
   269     }
   270     out += num_bytes;
   271     mp3_mad->output_begin += num_bytes;
   272     bytes_remaining -= num_bytes;
   273   }
   274   return 0;
   275 }
   276 
   277 void
   278 mad_seek(mad_data *mp3_mad, double position) {
   279   mad_timer_t target;
   280   int int_part;
   281 
   282   int_part = (int)position;
   283   mad_timer_set(&target, int_part,
   284                 (int)((position - int_part) * 1000000), 1000000);
   285 
   286   if (mad_timer_compare(mp3_mad->next_frame_start, target) > 0) {
   287     /* In order to seek backwards in a VBR file, we have to rewind and
   288        start again from the beginning.  This isn't necessary if the
   289        file happens to be CBR, of course; in that case we could seek
   290        directly to the frame we want.  But I leave that little
   291        optimization for the future developer who discovers she really
   292        needs it. */
   293     mp3_mad->frames_read = 0;
   294     mad_timer_reset(&mp3_mad->next_frame_start);
   295     mp3_mad->status &= ~MS_error_flags;
   296     mp3_mad->output_begin = 0;
   297     mp3_mad->output_end = 0;
   298 
   299     SDL_RWseek(mp3_mad->src, 0, RW_SEEK_SET);
   300   }
   301 
   302   /* Now we have to skip frames until we come to the right one.
   303      Again, only truly necessary if the file is VBR. */
   304   while (mad_timer_compare(mp3_mad->next_frame_start, target) < 0) {
   305     if (!read_next_frame(mp3_mad)) {
   306       if ((mp3_mad->status & MS_error_flags) != 0) {
   307         /* Couldn't read a frame; either an error condition or
   308            end-of-file.  Stop. */
   309         mp3_mad->status &= ~MS_playing;
   310         return;
   311       }
   312     }
   313   }
   314 
   315   /* Here we are, at the beginning of the frame that contains the
   316      target time.  Ehh, I say that's close enough.  If we wanted to,
   317      we could get more precise by decoding the frame now and counting
   318      the appropriate number of samples out of it. */
   319 }
   320 
   321 void
   322 mad_setVolume(mad_data *mp3_mad, int volume) {
   323   mp3_mad->volume = volume;
   324 }
   325 
   326 
   327 #endif  /* MP3_MAD_MUSIC */