| 1 | /* |
| 2 | * This file is part of DisOrder |
| 3 | * Copyright (C) 2007-2010 Richard Kettlewell |
| 4 | * |
| 5 | * This program is free software: you can redistribute it and/or modify |
| 6 | * it under the terms of the GNU General Public License as published by |
| 7 | * the Free Software Foundation, either version 3 of the License, or |
| 8 | * (at your option) any later version. |
| 9 | * |
| 10 | * This program is distributed in the hope that it will be useful, |
| 11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 13 | * GNU General Public License for more details. |
| 14 | * |
| 15 | * You should have received a copy of the GNU General Public License |
| 16 | * along with this program. If not, see <http://www.gnu.org/licenses/>. |
| 17 | */ |
| 18 | /** @file server/decode-mp3.c |
| 19 | * @brief Decode MP3 files. |
| 20 | */ |
| 21 | #include "decode.h" |
| 22 | #include <mad.h> |
| 23 | |
| 24 | static struct hreader input[1]; |
| 25 | |
| 26 | /** @brief Dithering state |
| 27 | * Filched from mpg321, which credits it to Robert Leslie */ |
| 28 | struct audio_dither { |
| 29 | mad_fixed_t error[3]; |
| 30 | mad_fixed_t random; |
| 31 | }; |
| 32 | |
| 33 | /** @brief 32-bit PRNG |
| 34 | * Filched from mpg321, which credits it to Robert Leslie */ |
| 35 | static inline unsigned long prng(unsigned long state) |
| 36 | { |
| 37 | return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL; |
| 38 | } |
| 39 | |
| 40 | /** @brief Generic linear sample quantize and dither routine |
| 41 | * Filched from mpg321, which credits it to Robert Leslie */ |
| 42 | static long audio_linear_dither(mad_fixed_t sample, |
| 43 | struct audio_dither *dither) { |
| 44 | unsigned int scalebits; |
| 45 | mad_fixed_t output, mask, rnd; |
| 46 | const int bits = 16; |
| 47 | |
| 48 | enum { |
| 49 | MIN = -MAD_F_ONE, |
| 50 | MAX = MAD_F_ONE - 1 |
| 51 | }; |
| 52 | |
| 53 | /* noise shape */ |
| 54 | sample += dither->error[0] - dither->error[1] + dither->error[2]; |
| 55 | |
| 56 | dither->error[2] = dither->error[1]; |
| 57 | dither->error[1] = dither->error[0] / 2; |
| 58 | |
| 59 | /* bias */ |
| 60 | output = sample + (1L << (MAD_F_FRACBITS + 1 - bits - 1)); |
| 61 | |
| 62 | scalebits = MAD_F_FRACBITS + 1 - bits; |
| 63 | mask = (1L << scalebits) - 1; |
| 64 | |
| 65 | /* dither */ |
| 66 | rnd = prng(dither->random); |
| 67 | output += (rnd & mask) - (dither->random & mask); |
| 68 | |
| 69 | dither->random = rnd; |
| 70 | |
| 71 | /* clip */ |
| 72 | if (output > MAX) { |
| 73 | output = MAX; |
| 74 | |
| 75 | if (sample > MAX) |
| 76 | sample = MAX; |
| 77 | } |
| 78 | else if (output < MIN) { |
| 79 | output = MIN; |
| 80 | |
| 81 | if (sample < MIN) |
| 82 | sample = MIN; |
| 83 | } |
| 84 | |
| 85 | /* quantize */ |
| 86 | output &= ~mask; |
| 87 | |
| 88 | /* error feedback */ |
| 89 | dither->error[0] = sample - output; |
| 90 | |
| 91 | /* scale */ |
| 92 | return output >> scalebits; |
| 93 | } |
| 94 | |
| 95 | /** @brief MP3 output callback */ |
| 96 | static enum mad_flow mp3_output(void attribute((unused)) *data, |
| 97 | struct mad_header const *header, |
| 98 | struct mad_pcm *pcm) { |
| 99 | size_t n = pcm->length; |
| 100 | const mad_fixed_t *l = pcm->samples[0], *r = pcm->samples[1]; |
| 101 | static struct audio_dither ld[1], rd[1]; |
| 102 | |
| 103 | output_header(header->samplerate, |
| 104 | pcm->channels, |
| 105 | 16, |
| 106 | 2 * pcm->channels * pcm->length, |
| 107 | ENDIAN_BIG); |
| 108 | switch(pcm->channels) { |
| 109 | case 1: |
| 110 | while(n--) |
| 111 | output_16(audio_linear_dither(*l++, ld)); |
| 112 | break; |
| 113 | case 2: |
| 114 | while(n--) { |
| 115 | output_16(audio_linear_dither(*l++, ld)); |
| 116 | output_16(audio_linear_dither(*r++, rd)); |
| 117 | } |
| 118 | break; |
| 119 | } |
| 120 | return MAD_FLOW_CONTINUE; |
| 121 | } |
| 122 | |
| 123 | /** @brief MP3 input callback */ |
| 124 | static enum mad_flow mp3_input(void attribute((unused)) *data, |
| 125 | struct mad_stream *stream) { |
| 126 | int used, remain, n; |
| 127 | |
| 128 | /* libmad requires its caller to do ALL the buffering work, including coping |
| 129 | * with partial frames. Given that it appears to be completely undocumented |
| 130 | * you could perhaps be forgiven for not discovering this... */ |
| 131 | if(input_count) { |
| 132 | /* Compute total number of bytes consumed */ |
| 133 | used = (char *)stream->next_frame - input_buffer; |
| 134 | /* Compute number of bytes left to consume */ |
| 135 | remain = input_count - used; |
| 136 | memmove(input_buffer, input_buffer + used, remain); |
| 137 | } else { |
| 138 | remain = 0; |
| 139 | } |
| 140 | /* Read new data */ |
| 141 | n = hreader_read(input, |
| 142 | input_buffer + remain, |
| 143 | (sizeof input_buffer) - remain); |
| 144 | if(n < 0) |
| 145 | disorder_fatal(errno, "reading from %s", path); |
| 146 | /* Compute total number of bytes available */ |
| 147 | input_count = remain + n; |
| 148 | if(input_count) |
| 149 | mad_stream_buffer(stream, (unsigned char *)input_buffer, input_count); |
| 150 | if(n) |
| 151 | return MAD_FLOW_CONTINUE; |
| 152 | else |
| 153 | return MAD_FLOW_STOP; |
| 154 | } |
| 155 | |
| 156 | /** @brief MP3 error callback */ |
| 157 | static enum mad_flow mp3_error(void attribute((unused)) *data, |
| 158 | struct mad_stream *stream, |
| 159 | struct mad_frame attribute((unused)) *frame) { |
| 160 | if(0) |
| 161 | /* Just generates pointless verbosity l-( */ |
| 162 | disorder_error(0, "decoding %s: %s (%#04x)", |
| 163 | path, mad_stream_errorstr(stream), stream->error); |
| 164 | return MAD_FLOW_CONTINUE; |
| 165 | } |
| 166 | |
| 167 | /** @brief MP3 decoder */ |
| 168 | void decode_mp3(void) { |
| 169 | struct mad_decoder mad[1]; |
| 170 | |
| 171 | if(hreader_init(path, input)) |
| 172 | disorder_fatal(errno, "opening %s", path); |
| 173 | mad_decoder_init(mad, 0/*data*/, mp3_input, 0/*header*/, 0/*filter*/, |
| 174 | mp3_output, mp3_error, 0/*message*/); |
| 175 | if(mad_decoder_run(mad, MAD_DECODER_MODE_SYNC)) |
| 176 | exit(1); |
| 177 | mad_decoder_finish(mad); |
| 178 | } |
| 179 | |
| 180 | /* |
| 181 | Local Variables: |
| 182 | c-basic-offset:2 |
| 183 | comment-column:40 |
| 184 | fill-column:79 |
| 185 | indent-tabs-mode:nil |
| 186 | End: |
| 187 | */ |