apps/metadata/mp4.c

   1 /***************************************************************************
   2  *             __________               __   ___.
   3  *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
   4  *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
   5  *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
   6  *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
   7  *                     \/            \/     \/    \/            \/
   8  * $Id$
   9  *
  10  * Copyright (C) 2005 Magnus Holmgren
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version 2
  15  * of the License, or (at your option) any later version.
  16  *
  17  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
  18  * KIND, either express or implied.
  19  *
  20  ****************************************************************************/
  21 #include <stdio.h>
  22 #include <string.h>
  23 #include <stdlib.h>
  24 #include <ctype.h>
  25 #include <inttypes.h>
  26
  27 #include "system.h"
  28 #include "errno.h"
  29 #include "metadata.h"
  30 #include "metadata_common.h"
  31 #include "metadata_parsers.h"
  32 #include "logf.h"
  33 #include "debug.h"
  34 #include "replaygain.h"
  35
  36 #define MP4_3gp6 FOURCC('3', 'g', 'p', '6')
  37 #define MP4_aART FOURCC('a', 'A', 'R', 'T')
  38 #define MP4_alac FOURCC('a', 'l', 'a', 'c')
  39 #define MP4_calb FOURCC(0xa9, 'a', 'l', 'b')
  40 #define MP4_cART FOURCC(0xa9, 'A', 'R', 'T')
  41 #define MP4_cgrp FOURCC(0xa9, 'g', 'r', 'p')
  42 #define MP4_cgen FOURCC(0xa9, 'g', 'e', 'n')
  43 #define MP4_chpl FOURCC('c', 'h', 'p', 'l')
  44 #define MP4_cnam FOURCC(0xa9, 'n', 'a', 'm')
  45 #define MP4_cwrt FOURCC(0xa9, 'w', 'r', 't')
  46 #define MP4_ccmt FOURCC(0xa9, 'c', 'm', 't')
  47 #define MP4_cday FOURCC(0xa9, 'd', 'a', 'y')
  48 #define MP4_disk FOURCC('d', 'i', 's', 'k')
  49 #define MP4_esds FOURCC('e', 's', 'd', 's')
  50 #define MP4_ftyp FOURCC('f', 't', 'y', 'p')
  51 #define MP4_gnre FOURCC('g', 'n', 'r', 'e')
  52 #define MP4_hdlr FOURCC('h', 'd', 'l', 'r')
  53 #define MP4_ilst FOURCC('i', 'l', 's', 't')
  54 #define MP4_isom FOURCC('i', 's', 'o', 'm')
  55 #define MP4_M4A  FOURCC('M', '4', 'A', ' ')
  56 #define MP4_m4a  FOURCC('m', '4', 'a', ' ') /*technically its "M4A "*/
  57 #define MP4_M4B  FOURCC('M', '4', 'B', ' ') /*but files exist with lower case*/
  58 #define MP4_mdat FOURCC('m', 'd', 'a', 't')
  59 #define MP4_mdia FOURCC('m', 'd', 'i', 'a')
  60 #define MP4_mdir FOURCC('m', 'd', 'i', 'r')
  61 #define MP4_meta FOURCC('m', 'e', 't', 'a')
  62 #define MP4_minf FOURCC('m', 'i', 'n', 'f')
  63 #define MP4_moov FOURCC('m', 'o', 'o', 'v')
  64 #define MP4_mp4a FOURCC('m', 'p', '4', 'a')
  65 #define MP4_mp42 FOURCC('m', 'p', '4', '2')
  66 #define MP4_qt   FOURCC('q', 't', ' ', ' ')
  67 #define MP4_soun FOURCC('s', 'o', 'u', 'n')
  68 #define MP4_stbl FOURCC('s', 't', 'b', 'l')
  69 #define MP4_stsd FOURCC('s', 't', 's', 'd')
  70 #define MP4_stts FOURCC('s', 't', 't', 's')
  71 #define MP4_trak FOURCC('t', 'r', 'a', 'k')
  72 #define MP4_trkn FOURCC('t', 'r', 'k', 'n')
  73 #define MP4_udta FOURCC('u', 'd', 't', 'a')
  74 #define MP4_extra FOURCC('-', '-', '-', '-')
  75
  76 /* Read the tag data from an MP4 file, storing up to buffer_size bytes in
  77  * buffer.
  78  */
  79 static unsigned long read_mp4_tag(int fd, unsigned int size_left, char* buffer,
  80                                   unsigned int buffer_left)
  81 {
  82     unsigned int bytes_read = 0;
  83
  84     if (buffer_left == 0)
  85     {
  86         lseek(fd, size_left, SEEK_CUR);     /* Skip everything */
  87     }
  88     else
  89     {
  90         /* Skip the data tag header - maybe we should parse it properly? */
  91         lseek(fd, 16, SEEK_CUR);
  92         size_left -= 16;
  93
  94         if (size_left > buffer_left)
  95         {
  96             read(fd, buffer, buffer_left);
  97             lseek(fd, size_left - buffer_left, SEEK_CUR);
  98             bytes_read = buffer_left;
  99         }
 100         else
 101         {
 102             read(fd, buffer, size_left);
 103             bytes_read = size_left;
 104         }
 105     }
 106
 107     return bytes_read;
 108 }
 109
 110 /* Read a string tag from an MP4 file */
 111 static unsigned int read_mp4_tag_string(int fd, int size_left, char** buffer,
 112                                         unsigned int* buffer_left, char** dest)
 113 {
 114     unsigned int bytes_read = read_mp4_tag(fd, size_left, *buffer,
 115         *buffer_left > 0 ? *buffer_left - 1 : 0);
 116     unsigned int length = 0;
 117
 118     if (bytes_read)
 119     {
 120         /* Do not overwrite already available metadata. Especially when reading
 121          * tags with e.g. multiple genres / artists. This way only the first
 122          * of multiple entries is used, all following are dropped. */
 123         if (*dest == NULL)
 124         {
 125             (*buffer)[bytes_read] = 0;
 126             *dest = *buffer;
 127             length = strlen(*buffer) + 1;
 128             *buffer_left -= length;
 129             *buffer += length;
 130         }
 131     }
 132     else
 133     {
 134         *dest = NULL;
 135     }
 136
 137     return length;
 138 }
 139
 140 static unsigned int read_mp4_atom(int fd, uint32_t* size,
 141                                   uint32_t* type, uint32_t size_left)
 142 {
 143     read_uint32be(fd, size);
 144     read_uint32be(fd, type);
 145
 146     if (*size == 1)
 147     {
 148         /* FAT32 doesn't support files this big, so something seems to
 149          * be wrong. (64-bit sizes should only be used when required.)
 150          */
 151         errno = EFBIG;
 152         *type = 0;
 153         return 0;
 154     }
 155
 156     if (*size > 0)
 157     {
 158         if (*size > size_left)
 159         {
 160             size_left = 0;
 161         }
 162         else
 163         {
 164             size_left -= *size;
 165         }
 166
 167         *size -= 8;
 168     }
 169     else
 170     {
 171         *size = size_left;
 172         size_left = 0;
 173     }
 174
 175     return size_left;
 176 }
 177
 178 static unsigned int read_mp4_length(int fd, uint32_t* size)
 179 {
 180     unsigned int length = 0;
 181     int bytes = 0;
 182     unsigned char c;
 183
 184     do
 185     {
 186         read(fd, &c, 1);
 187         bytes++;
 188         (*size)--;
 189         length = (length << 7) | (c & 0x7F);
 190     }
 191     while ((c & 0x80) && (bytes < 4) && (*size > 0));
 192
 193     return length;
 194 }
 195
 196 static bool read_mp4_esds(int fd, struct mp3entry* id3, uint32_t* size)
 197 {
 198     unsigned char buf[8];
 199     bool sbr = false;
 200
 201     lseek(fd, 4, SEEK_CUR);     /* Version and flags. */
 202     read(fd, buf, 1);           /* Verify ES_DescrTag. */
 203     *size -= 5;
 204
 205     if (*buf == 3)
 206     {
 207         /* read length */
 208         if (read_mp4_length(fd, size) < 20)
 209         {
 210             return sbr;
 211         }
 212
 213         lseek(fd, 3, SEEK_CUR);
 214         *size -= 3;
 215     }
 216     else
 217     {
 218         lseek(fd, 2, SEEK_CUR);
 219         *size -= 2;
 220     }
 221
 222     read(fd, buf, 1);           /* Verify DecoderConfigDescrTab. */
 223     *size -= 1;
 224
 225     if (*buf != 4)
 226     {
 227         return sbr;
 228     }
 229
 230     if (read_mp4_length(fd, size) < 13)
 231     {
 232         return sbr;
 233     }
 234
 235     lseek(fd, 13, SEEK_CUR);    /* Skip audio type, bit rates, etc. */
 236     read(fd, buf, 1);
 237     *size -= 14;
 238
 239     if (*buf != 5)              /* Verify DecSpecificInfoTag. */
 240     {
 241         return sbr;
 242     }
 243
 244     {
 245         static const int sample_rates[] =
 246         {
 247             96000, 88200, 64000, 48000, 44100, 32000,
 248             24000, 22050, 16000, 12000, 11025, 8000
 249         };
 250         unsigned long bits;
 251         unsigned int length;
 252         unsigned int index;
 253         unsigned int type;
 254
 255         /* Read the (leading part of the) decoder config. */
 256         length = read_mp4_length(fd, size);
 257         length = MIN(length, *size);
 258         length = MIN(length, sizeof(buf));
 259         memset(buf, 0, sizeof(buf));
 260         read(fd, buf, length);
 261         *size -= length;
 262
 263         /* Maybe time to write a simple read_bits function... */
 264
 265         /* Decoder config format:
 266          * Object type           - 5 bits
 267          * Frequency index       - 4 bits
 268          * Channel configuration - 4 bits
 269          */
 270         bits = get_long_be(buf);
 271         type = bits >> 27;              /* Object type - 5 bits */
 272         index = (bits >> 23) & 0xf;     /* Frequency index - 4 bits */
 273
 274         if (index < (sizeof(sample_rates) / sizeof(*sample_rates)))
 275         {
 276             id3->frequency = sample_rates[index];
 277         }
 278
 279         if (type == 5)
 280         {
 281             unsigned int old_index = index;
 282
 283             sbr = true;
 284             index = (bits >> 15) & 0xf; /* Frequency index - 4 bits */
 285
 286             if (index == 15)
 287             {
 288                 /* 17 bits read so far... */
 289                 bits = get_long_be(&buf[2]);
 290                 id3->frequency = (bits >> 7) & 0x00ffffff;
 291             }
 292             else if (index < (sizeof(sample_rates) / sizeof(*sample_rates)))
 293             {
 294                 id3->frequency = sample_rates[index];
 295             }
 296
 297             if (old_index == index)
 298             {
 299                 /* Downsampled SBR */
 300                 id3->frequency *= 2;
 301             }
 302         }
 303         /* Skip 13 bits from above, plus 3 bits, then read 11 bits */
 304         else if ((length >= 4) && (((bits >> 5) & 0x7ff) == 0x2b7))
 305         {
 306             /* We found an extensionAudioObjectType */
 307             type = bits & 0x1f;         /* Object type - 5 bits*/
 308             bits = get_long_be(&buf[4]);
 309
 310             if (type == 5)
 311             {
 312                 sbr = bits >> 31;
 313
 314                 if (sbr)
 315                 {
 316                     unsigned int old_index = index;
 317
 318                     /* 1 bit read so far */
 319                     index = (bits >> 27) & 0xf; /* Frequency index - 4 bits */
 320
 321                     if (index == 15)
 322                     {
 323                         /* 5 bits read so far */
 324                         id3->frequency = (bits >> 3) & 0x00ffffff;
 325                     }
 326                     else if (index < (sizeof(sample_rates) / sizeof(*sample_rates)))
 327                     {
 328                         id3->frequency = sample_rates[index];
 329                     }
 330
 331                     if (old_index == index)
 332                     {
 333                         /* Downsampled SBR */
 334                         id3->frequency *= 2;
 335                     }
 336                 }
 337             }
 338         }
 339
 340         if (!sbr && (id3->frequency <= 24000) && (length <= 2))
 341         {
 342             /* Double the frequency for low-frequency files without a "long"
 343              * DecSpecificConfig header. The file may or may not contain SBR,
 344              * but here we guess it does if the header is short. This can
 345              * fail on some files, but it's the best we can do, short of
 346              * decoding (parts of) the file.
 347              */
 348             id3->frequency *= 2;
 349             sbr = true;
 350         }
 351     }
 352
 353     return sbr;
 354 }
 355
 356 static bool read_mp4_tags(int fd, struct mp3entry* id3,
 357                           uint32_t size_left)
 358 {
 359     uint32_t size;
 360     uint32_t type;
 361     unsigned int buffer_left = sizeof(id3->id3v2buf) + sizeof(id3->id3v1buf);
 362     char* buffer = id3->id3v2buf;
 363     bool cwrt = false;
 364
 365     do
 366     {
 367         size_left = read_mp4_atom(fd, &size, &type, size_left);
 368
 369         /* DEBUGF("Tag atom: '%c%c%c%c' (%d bytes left)\n", type >> 24 & 0xff,
 370             type >> 16 & 0xff, type >> 8 & 0xff, type & 0xff, size); */
 371
 372         switch (type)
 373         {
 374         case MP4_cnam:
 375             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 376                 &id3->title);
 377             break;
 378
 379         case MP4_cART:
 380             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 381                 &id3->artist);
 382             break;
 383
 384         case MP4_aART:
 385             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 386                 &id3->albumartist);
 387             break;
 388
 389         case MP4_cgrp:
 390             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 391                 &id3->grouping);
 392             break;
 393
 394         case MP4_calb:
 395             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 396                 &id3->album);
 397             break;
 398
 399         case MP4_cwrt:
 400             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 401                 &id3->composer);
 402             cwrt = false;
 403             break;
 404
 405         case MP4_ccmt:
 406             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 407                 &id3->comment);
 408             break;
 409
 410         case MP4_cday:
 411             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 412                                 &id3->year_string);
 413
 414             /* Try to parse it as a year, for the benefit of the database.
 415              */
 416             if(id3->year_string)
 417             {
 418                 id3->year = atoi(id3->year_string);
 419                 if (id3->year < 1900)
 420                 {
 421                     id3->year = 0;
 422                 }
 423             }
 424             else
 425                 id3->year = 0;
 426
 427             break;
 428
 429         case MP4_gnre:
 430             {
 431                 unsigned short genre;
 432
 433                 read_mp4_tag(fd, size, (char*) &genre, sizeof(genre));
 434                 id3->genre_string = id3_get_num_genre(betoh16(genre) - 1);
 435             }
 436             break;
 437
 438         case MP4_cgen:
 439             read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 440                 &id3->genre_string);
 441             break;
 442
 443         case MP4_disk:
 444             {
 445                 unsigned short n[2];
 446
 447                 read_mp4_tag(fd, size, (char*) &n, sizeof(n));
 448                 id3->discnum = betoh16(n[1]);
 449             }
 450             break;
 451
 452         case MP4_trkn:
 453             {
 454                 unsigned short n[2];
 455
 456                 read_mp4_tag(fd, size, (char*) &n, sizeof(n));
 457                 id3->tracknum = betoh16(n[1]);
 458             }
 459             break;
 460
 461         case MP4_extra:
 462             {
 463                 char tag_name[TAG_NAME_LENGTH];
 464                 uint32_t sub_size;
 465
 466                 /* "mean" atom */
 467                 read_uint32be(fd, &sub_size);
 468                 size -= sub_size;
 469                 lseek(fd, sub_size - 4, SEEK_CUR);
 470                 /* "name" atom */
 471                 read_uint32be(fd, &sub_size);
 472                 size -= sub_size;
 473                 lseek(fd, 8, SEEK_CUR);
 474                 sub_size -= 12;
 475
 476                 if (sub_size > sizeof(tag_name) - 1)
 477                 {
 478                     read(fd, tag_name, sizeof(tag_name) - 1);
 479                     lseek(fd, sub_size - (sizeof(tag_name) - 1), SEEK_CUR);
 480                     tag_name[sizeof(tag_name) - 1] = 0;
 481                 }
 482                 else
 483                 {
 484                     read(fd, tag_name, sub_size);
 485                     tag_name[sub_size] = 0;
 486                 }
 487
 488                 if ((strcasecmp(tag_name, "composer") == 0) && !cwrt)
 489                 {
 490                     read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 491                         &id3->composer);
 492                 }
 493                 else if (strcasecmp(tag_name, "iTunSMPB") == 0)
 494                 {
 495                     char value[TAG_VALUE_LENGTH];
 496                     char* value_p = value;
 497                     char* any;
 498                     unsigned int length = sizeof(value);
 499
 500                     read_mp4_tag_string(fd, size, &value_p, &length, &any);
 501                     id3->lead_trim = get_itunes_int32(value, 1);
 502                     id3->tail_trim = get_itunes_int32(value, 2);
 503                     DEBUGF("AAC: lead_trim %d, tail_trim %d\n",
 504                         id3->lead_trim, id3->tail_trim);
 505                 }
 506                 else if (strcasecmp(tag_name, "musicbrainz track id") == 0)
 507                 {
 508                     read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 509                         &id3->mb_track_id);
 510                 }
 511                 else if ((strcasecmp(tag_name, "album artist") == 0))
 512                 {
 513                     read_mp4_tag_string(fd, size, &buffer, &buffer_left,
 514                         &id3->albumartist);
 515                 }
 516                 else
 517                 {
 518                     char* any;
 519                     unsigned int length = read_mp4_tag_string(fd, size,
 520                         &buffer, &buffer_left, &any);
 521
 522                     if (length > 0)
 523                     {
 524                         /* Re-use the read buffer as the dest buffer... */
 525                         buffer -= length;
 526                         buffer_left += length;
 527
 528                         if (parse_replaygain(tag_name, buffer, id3,
 529                             buffer, buffer_left) > 0)
 530                         {
 531                             /* Data used, keep it. */
 532                             buffer += length;
 533                             buffer_left -= length;
 534                         }
 535                     }
 536                 }
 537             }
 538             break;
 539
 540         default:
 541             lseek(fd, size, SEEK_CUR);
 542             break;
 543         }
 544     }
 545     while ((size_left > 0) && (errno == 0));
 546
 547     return true;
 548 }
 549
 550 static bool read_mp4_container(int fd, struct mp3entry* id3,
 551                                uint32_t size_left)
 552 {
 553     uint32_t size;
 554     uint32_t type;
 555     uint32_t handler = 0;
 556     bool rc = true;
 557     bool done = false;
 558
 559     do
 560     {
 561         size_left = read_mp4_atom(fd, &size, &type, size_left);
 562
 563         /* DEBUGF("Atom: '%c%c%c%c' (0x%08lx, %lu bytes left)\n",
 564             (int) ((type >> 24) & 0xff), (int) ((type >> 16) & 0xff),
 565             (int) ((type >> 8) & 0xff), (int) (type & 0xff),
 566             type, size); */
 567
 568         switch (type)
 569         {
 570         case MP4_ftyp:
 571             {
 572                 uint32_t id;
 573
 574                 read_uint32be(fd, &id);
 575                 size -= 4;
 576
 577                 if ((id != MP4_M4A) && (id != MP4_M4B) && (id != MP4_mp42)
 578                     && (id != MP4_qt) && (id != MP4_3gp6) && (id != MP4_m4a)
 579                     && (id != MP4_isom))
 580                 {
 581                     DEBUGF("Unknown MP4 file type: '%c%c%c%c'\n",
 582                         (int)(id >> 24 & 0xff), (int)(id >> 16 & 0xff),
 583                         (int)(id >> 8 & 0xff), (int)(id & 0xff));
 584                     return false;
 585                 }
 586             }
 587             break;
 588
 589         case MP4_meta:
 590             lseek(fd, 4, SEEK_CUR);  /* Skip version */
 591             size -= 4;
 592             /* Fall through */
 593
 594         case MP4_moov:
 595         case MP4_udta:
 596         case MP4_mdia:
 597         case MP4_stbl:
 598         case MP4_trak:
 599             rc = read_mp4_container(fd, id3, size);
 600             size = 0;
 601             break;
 602
 603         case MP4_ilst:
 604             /* We need at least a size of 8 to read the next atom. */
 605             if (handler == MP4_mdir && size>8)
 606             {
 607                 rc = read_mp4_tags(fd, id3, size);
 608                 size = 0;
 609             }
 610             break;
 611
 612         case MP4_minf:
 613             if (handler == MP4_soun)
 614             {
 615                 rc = read_mp4_container(fd, id3, size);
 616                 size = 0;
 617             }
 618             break;
 619
 620         case MP4_stsd:
 621             lseek(fd, 8, SEEK_CUR);
 622             size -= 8;
 623             rc = read_mp4_container(fd, id3, size);
 624             size = 0;
 625             break;
 626
 627         case MP4_hdlr:
 628             lseek(fd, 8, SEEK_CUR);
 629             read_uint32be(fd, &handler);
 630             size -= 12;
 631             /* DEBUGF("    Handler '%c%c%c%c'\n", handler >> 24 & 0xff,
 632                 handler >> 16 & 0xff, handler >> 8 & 0xff,handler & 0xff); */
 633             break;
 634
 635         case MP4_stts:
 636             {
 637                 uint32_t entries;
 638                 unsigned int i;
 639
 640                 /* Reset to false. */
 641                 id3->needs_upsampling_correction = false;
 642
 643                 lseek(fd, 4, SEEK_CUR);
 644                 read_uint32be(fd, &entries);
 645                 id3->samples = 0;
 646
 647                 for (i = 0; i < entries; i++)
 648                 {
 649                     uint32_t n;
 650                     uint32_t l;
 651
 652                     read_uint32be(fd, &n);
 653                     read_uint32be(fd, &l);
 654
 655                     /* Some AAC file use HE profile. In this case the number
 656                      * of output samples is doubled to a maximum of 2048
 657                      * samples per frame. This means that files which already
 658                      * report a frame size of 2048 in their header will not
 659                      * need any further special handling. */
 660                     if (id3->codectype==AFMT_MP4_AAC_HE && l<=1024)
 661                     {
 662                         id3->samples += n * l * 2;
 663                         id3->needs_upsampling_correction = true;
 664                     }
 665                     else
 666                     {
 667                         id3->samples += n * l;
 668                     }
 669                 }
 670
 671                 size = 0;
 672             }
 673             break;
 674
 675         case MP4_mp4a:
 676             {
 677                 uint32_t subsize;
 678                 uint32_t subtype;
 679
 680                 /* Move to the next expected mp4 atom. */
 681                 lseek(fd, 28, SEEK_CUR);
 682                 read_mp4_atom(fd, &subsize, &subtype, size);
 683                 size -= 36;
 684
 685                 if (subtype == MP4_esds)
 686                 {
 687                     /* Read esds metadata and return if AAC-HE/SBR is used. */
 688                     if (read_mp4_esds(fd, id3, &size))
 689                         id3->codectype = AFMT_MP4_AAC_HE;
 690                     else
 691                         id3->codectype = AFMT_MP4_AAC;
 692                 }
 693             }
 694             break;
 695
 696         case MP4_alac:
 697             {
 698                 uint32_t frequency;
 699                 uint32_t subsize;
 700                 uint32_t subtype;
 701
 702                 /* Move to the next expected mp4 atom. */
 703                 lseek(fd, 28, SEEK_CUR);
 704                 read_mp4_atom(fd, &subsize, &subtype, size);
 705                 size -= 36;
 706 #if 0
 707                 /* We might need to parse for the alac metadata atom. */
 708                 while (!((subsize==28) && (subtype==MP4_alac)) && (size>0))
 709                 {
 710                     lseek(fd, -7, SEEK_CUR);
 711                     read_mp4_atom(fd, &subsize, &subtype, size);
 712                     size -= 1;
 713                     errno = 0; /* will most likely be set while parsing */
 714                 }
 715 #endif
 716                 if (subtype == MP4_alac)
 717                 {
 718                     lseek(fd, 24, SEEK_CUR);
 719                     read_uint32be(fd, &frequency);
 720                     size -= 28;
 721                     id3->frequency = frequency;
 722                     id3->codectype = AFMT_MP4_ALAC;
 723                 }
 724             }
 725             break;
 726
 727         case MP4_mdat:
 728             /* Some AAC files appear to contain additional empty mdat chunks.
 729                Ignore them. */
 730             if(size == 0)
 731                 break;
 732             id3->filesize = size;
 733             if(id3->samples > 0) {
 734                 /* We've already seen the moov chunk. */
 735                 done = true;
 736             }
 737             break;
 738
 739         case MP4_chpl:
 740             {
 741                 /* ADDME: add support for real chapters. Right now it's only
 742                  * used for Nero's gapless hack */
 743                 uint8_t chapters;
 744                 uint64_t timestamp;
 745
 746                 lseek(fd, 8, SEEK_CUR);
 747                 read_uint8(fd, &chapters);
 748                 size -= 9;
 749
 750                 /* the first chapter will be used as the lead_trim */
 751                 if (chapters > 0) {
 752                     read_uint64be(fd, &timestamp);
 753                     id3->lead_trim = (timestamp * id3->frequency) / 10000000;
 754                     size -= 8;
 755                 }
 756             }
 757             break;
 758
 759         default:
 760             break;
 761         }
 762
 763         /* Skip final seek. */
 764         if (!done)
 765         {
 766             lseek(fd, size, SEEK_CUR);
 767         }
 768     } while (rc && (size_left > 0) && (errno == 0) && !done);
 769
 770     return rc;
 771 }
 772
 773 bool get_mp4_metadata(int fd, struct mp3entry* id3)
 774 {
 775     id3->codectype = AFMT_UNKNOWN;
 776     id3->filesize = 0;
 777     errno = 0;
 778
 779     if (read_mp4_container(fd, id3, filesize(fd)) && (errno == 0)
 780         && (id3->samples > 0) && (id3->frequency > 0)
 781         && (id3->filesize > 0))
 782     {
 783         if (id3->codectype == AFMT_UNKNOWN)
 784         {
 785             logf("Not an ALAC or AAC file");
 786             return false;
 787         }
 788
 789         id3->length = ((int64_t) id3->samples * 1000) / id3->frequency;
 790
 791         if (id3->length <= 0)
 792         {
 793             logf("mp4 length invalid!");
 794             return false;
 795         }
 796
 797         id3->bitrate = ((int64_t) id3->filesize * 8) / id3->length;
 798         DEBUGF("MP4 bitrate %d, frequency %ld Hz, length %ld ms\n",
 799             id3->bitrate, id3->frequency, id3->length);
 800     }
 801     else
 802     {
 803         logf("MP4 metadata error");
 804         DEBUGF("MP4 metadata error. errno %d, samples %ld, frequency %ld, "
 805             "filesize %ld\n", errno, id3->samples, id3->frequency,
 806             id3->filesize);
 807         return false;
 808     }
 809
 810     return true;
 811 }