libavcodec/mlp_parser.c

   1 /*
   2  * MLP parser
   3  * Copyright (c) 2007 Ian Caulfield
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file mlp_parser.c
  24  * MLP parser
  25  */
  26
  27 #include "libavutil/crc.h"
  28 #include "bitstream.h"
  29 #include "parser.h"
  30 #include "mlp_parser.h"
  31
  32 static const uint8_t mlp_quants[16] = {
  33     16, 20, 24, 0, 0, 0, 0, 0,
  34      0,  0,  0, 0, 0, 0, 0, 0,
  35 };
  36
  37 static const uint8_t mlp_channels[32] = {
  38     1, 2, 3, 4, 3, 4, 5, 3, 4, 5, 4, 5, 6, 4, 5, 4,
  39     5, 6, 5, 5, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  40 };
  41
  42 static const uint8_t thd_chancount[13] = {
  43 //  LR    C   LFE  LRs LRvh  LRc LRrs  Cs   Ts  LRsd  LRw  Cvh  LFE2
  44      2,   1,   1,   2,   2,   2,   2,   1,   1,   2,   2,   1,   1
  45 };
  46
  47 static int mlp_samplerate(int in)
  48 {
  49     if (in == 0xF)
  50         return 0;
  51
  52     return (in & 8 ? 44100 : 48000) << (in & 7) ;
  53 }
  54
  55 static int truehd_channels(int chanmap)
  56 {
  57     int channels = 0, i;
  58
  59     for (i = 0; i < 13; i++)
  60         channels += thd_chancount[i] * ((chanmap >> i) & 1);
  61
  62     return channels;
  63 }
  64
  65 static int crc_init = 0;
  66 static AVCRC crc_2D[1024];
  67
  68 /** MLP uses checksums that seem to be based on the standard CRC algorithm,
  69  *  but not (in implementation terms, the table lookup and XOR are reversed).
  70  *  We can implement this behavior using a standard av_crc on all but the
  71  *  last element, then XOR that with the last element.
  72  */
  73
  74 static uint16_t mlp_checksum16(const uint8_t *buf, unsigned int buf_size)
  75 {
  76     uint16_t crc;
  77
  78     if (!crc_init) {
  79         av_crc_init(crc_2D, 0, 16, 0x002D, sizeof(crc_2D));
  80         crc_init = 1;
  81     }
  82
  83     crc = av_crc(crc_2D, 0, buf, buf_size - 2);
  84     crc ^= AV_RL16(buf + buf_size - 2);
  85     return crc;
  86 }
  87
  88 /** Read a major sync info header - contains high level information about
  89  *  the stream - sample rate, channel arrangement etc. Most of this
  90  *  information is not actually necessary for decoding, only for playback.
  91  */
  92
  93 int ff_mlp_read_major_sync(void *log, MLPHeaderInfo *mh, const uint8_t *buf,
  94                            unsigned int buf_size)
  95 {
  96     GetBitContext gb;
  97     int ratebits;
  98     uint16_t checksum;
  99
 100     if (buf_size < 28) {
 101         av_log(log, AV_LOG_ERROR, "Packet too short, unable to read major sync\n");
 102         return -1;
 103     }
 104
 105     checksum = mlp_checksum16(buf, 26);
 106     if (checksum != AV_RL16(buf+26)) {
 107         av_log(log, AV_LOG_ERROR, "Major sync info header checksum error\n");
 108         return -1;
 109     }
 110
 111     init_get_bits(&gb, buf, buf_size * 8);
 112
 113     if (get_bits_long(&gb, 24) != 0xf8726f) /* Sync words */
 114         return -1;
 115
 116     mh->stream_type = get_bits(&gb, 8);
 117
 118     if (mh->stream_type == 0xbb) {
 119         mh->group1_bits = mlp_quants[get_bits(&gb, 4)];
 120         mh->group2_bits = mlp_quants[get_bits(&gb, 4)];
 121
 122         ratebits = get_bits(&gb, 4);
 123         mh->group1_samplerate = mlp_samplerate(ratebits);
 124         mh->group2_samplerate = mlp_samplerate(get_bits(&gb, 4));
 125
 126         skip_bits(&gb, 11);
 127
 128         mh->channels_mlp = get_bits(&gb, 5);
 129     } else if (mh->stream_type == 0xba) {
 130         mh->group1_bits = 24; // TODO: Is this information actually conveyed anywhere?
 131         mh->group2_bits = 0;
 132
 133         ratebits = get_bits(&gb, 4);
 134         mh->group1_samplerate = mlp_samplerate(ratebits);
 135         mh->group2_samplerate = 0;
 136
 137         skip_bits(&gb, 8);
 138
 139         mh->channels_thd_stream1 = get_bits(&gb, 5);
 140
 141         skip_bits(&gb, 2);
 142
 143         mh->channels_thd_stream2 = get_bits(&gb, 13);
 144     } else
 145         return -1;
 146
 147     mh->access_unit_size = 40 << (ratebits & 7);
 148     mh->access_unit_size_pow2 = 64 << (ratebits & 7);
 149
 150     skip_bits_long(&gb, 48);
 151
 152     mh->is_vbr = get_bits1(&gb);
 153
 154     mh->peak_bitrate = (get_bits(&gb, 15) * mh->group1_samplerate + 8) >> 4;
 155
 156     mh->num_substreams = get_bits(&gb, 4);
 157
 158     skip_bits_long(&gb, 4 + 11 * 8);
 159
 160     return 0;
 161 }
 162
 163 typedef struct MLPParseContext
 164 {
 165     ParseContext pc;
 166
 167     int bytes_left;
 168
 169     int in_sync;
 170
 171     int num_substreams;
 172 } MLPParseContext;
 173
 174 static int mlp_parse(AVCodecParserContext *s,
 175                      AVCodecContext *avctx,
 176                      const uint8_t **poutbuf, int *poutbuf_size,
 177                      const uint8_t *buf, int buf_size)
 178 {
 179     MLPParseContext *mp = s->priv_data;
 180     int sync_present;
 181     uint8_t parity_bits;
 182     int next;
 183     int i, p = 0;
 184
 185     *poutbuf_size = 0;
 186     if (buf_size == 0)
 187         return 0;
 188
 189     if (!mp->in_sync) {
 190         // Not in sync - find a major sync header
 191
 192         for (i = 0; i < buf_size; i++) {
 193             mp->pc.state = (mp->pc.state << 8) | buf[i];
 194             if ((mp->pc.state & 0xfffffffe) == 0xf8726fba) {
 195                 mp->in_sync = 1;
 196                 mp->bytes_left = 0;
 197                 break;
 198             }
 199         }
 200
 201         if (!mp->in_sync) {
 202             ff_combine_frame(&mp->pc, END_NOT_FOUND, &buf, &buf_size);
 203             return buf_size;
 204         }
 205
 206         ff_combine_frame(&mp->pc, i - 7, &buf, &buf_size);
 207
 208         return i - 7;
 209     }
 210
 211     if (mp->bytes_left == 0) {
 212         // Find length of this packet
 213
 214         /* Copy overread bytes from last frame into buffer. */
 215         for(; mp->pc.overread>0; mp->pc.overread--) {
 216             mp->pc.buffer[mp->pc.index++]= mp->pc.buffer[mp->pc.overread_index++];
 217         }
 218
 219         if (mp->pc.index + buf_size < 2) {
 220             ff_combine_frame(&mp->pc, END_NOT_FOUND, &buf, &buf_size);
 221             return buf_size;
 222         }
 223
 224         mp->bytes_left = ((mp->pc.index > 0 ? mp->pc.buffer[0] : buf[0]) << 8)
 225                        |  (mp->pc.index > 1 ? mp->pc.buffer[1] : buf[1-mp->pc.index]);
 226         mp->bytes_left = (mp->bytes_left & 0xfff) * 2;
 227         mp->bytes_left -= mp->pc.index;
 228     }
 229
 230     next = (mp->bytes_left > buf_size) ? END_NOT_FOUND : mp->bytes_left;
 231
 232     if (ff_combine_frame(&mp->pc, next, &buf, &buf_size) < 0) {
 233         mp->bytes_left -= buf_size;
 234         return buf_size;
 235     }
 236
 237     mp->bytes_left = 0;
 238
 239     sync_present = (AV_RB32(buf + 4) & 0xfffffffe) == 0xf8726fba;
 240
 241     if (!sync_present) {
 242         // First nibble of a frame is a parity check of the first few nibbles.
 243         // Only check when this isn't a sync frame - syncs have a checksum.
 244
 245         parity_bits = 0;
 246         for (i = 0; i <= mp->num_substreams; i++) {
 247             parity_bits ^= buf[p++];
 248             parity_bits ^= buf[p++];
 249
 250             if (i == 0 || buf[p-2] & 0x80) {
 251                 parity_bits ^= buf[p++];
 252                 parity_bits ^= buf[p++];
 253             }
 254         }
 255
 256         if ((((parity_bits >> 4) ^ parity_bits) & 0xF) != 0xF) {
 257             av_log(avctx, AV_LOG_INFO, "mlpparse: Parity check failed.\n");
 258             goto lost_sync;
 259         }
 260     } else {
 261         MLPHeaderInfo mh;
 262
 263         if (ff_mlp_read_major_sync(avctx, &mh, buf + 4, buf_size - 4) < 0)
 264             goto lost_sync;
 265
 266 #ifdef CONFIG_AUDIO_NONSHORT
 267         avctx->bits_per_sample = mh.group1_bits;
 268         if (avctx->bits_per_sample > 16)
 269             avctx->sample_fmt = SAMPLE_FMT_S32;
 270 #endif
 271         avctx->sample_rate = mh.group1_samplerate;
 272         avctx->frame_size = mh.access_unit_size;
 273
 274         if (mh.stream_type == 0xbb) {
 275             /* MLP stream */
 276             avctx->channels = mlp_channels[mh.channels_mlp];
 277         } else { /* mh.stream_type == 0xba */
 278             /* TrueHD stream */
 279             if (mh.channels_thd_stream2)
 280                 avctx->channels = truehd_channels(mh.channels_thd_stream2);
 281             else
 282                 avctx->channels = truehd_channels(mh.channels_thd_stream1);
 283         }
 284
 285         if (!mh.is_vbr) /* Stream is CBR */
 286             avctx->bit_rate = mh.peak_bitrate;
 287
 288         mp->num_substreams = mh.num_substreams;
 289     }
 290
 291     *poutbuf = buf;
 292     *poutbuf_size = buf_size;
 293
 294     return next;
 295
 296 lost_sync:
 297     mp->in_sync = 0;
 298     return -1;
 299 }
 300
 301 AVCodecParser mlp_parser = {
 302     { CODEC_ID_MLP },
 303     sizeof(MLPParseContext),
 304     NULL,
 305     mlp_parse,
 306     NULL,
 307 };