summaryrefslogtreecommitdiffstats
path: root/apps/metadata/mp4.c
blob: 706e6212343b22cdc70a44c6325af08c65b8ac69 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2005 Magnus Holmgren
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <inttypes.h>

#include "system.h"
#include "errno.h"
#include "metadata.h"
#include "metadata_common.h"
#include "metadata_parsers.h"
#include "logf.h"
#include "debug.h"
#include "replaygain.h"

#define MP4_3gp6 FOURCC('3', 'g', 'p', '6')
#define MP4_aART FOURCC('a', 'A', 'R', 'T')
#define MP4_alac FOURCC('a', 'l', 'a', 'c')
#define MP4_calb FOURCC(0xa9, 'a', 'l', 'b')
#define MP4_cART FOURCC(0xa9, 'A', 'R', 'T')
#define MP4_cgrp FOURCC(0xa9, 'g', 'r', 'p')
#define MP4_cgen FOURCC(0xa9, 'g', 'e', 'n')
#define MP4_chpl FOURCC('c', 'h', 'p', 'l')
#define MP4_cnam FOURCC(0xa9, 'n', 'a', 'm')
#define MP4_cwrt FOURCC(0xa9, 'w', 'r', 't')
#define MP4_ccmt FOURCC(0xa9, 'c', 'm', 't')
#define MP4_cday FOURCC(0xa9, 'd', 'a', 'y')
#define MP4_disk FOURCC('d', 'i', 's', 'k')
#define MP4_esds FOURCC('e', 's', 'd', 's')
#define MP4_ftyp FOURCC('f', 't', 'y', 'p')
#define MP4_gnre FOURCC('g', 'n', 'r', 'e')
#define MP4_hdlr FOURCC('h', 'd', 'l', 'r')
#define MP4_ilst FOURCC('i', 'l', 's', 't')
#define MP4_isom FOURCC('i', 's', 'o', 'm')
#define MP4_M4A  FOURCC('M', '4', 'A', ' ')
#define MP4_m4a  FOURCC('m', '4', 'a', ' ') /*technically its "M4A "*/
#define MP4_M4B  FOURCC('M', '4', 'B', ' ') /*but files exist with lower case*/
#define MP4_mdat FOURCC('m', 'd', 'a', 't')
#define MP4_mdia FOURCC('m', 'd', 'i', 'a')
#define MP4_mdir FOURCC('m', 'd', 'i', 'r')
#define MP4_meta FOURCC('m', 'e', 't', 'a')
#define MP4_minf FOURCC('m', 'i', 'n', 'f')
#define MP4_moov FOURCC('m', 'o', 'o', 'v')
#define MP4_mp4a FOURCC('m', 'p', '4', 'a')
#define MP4_mp42 FOURCC('m', 'p', '4', '2')
#define MP4_qt   FOURCC('q', 't', ' ', ' ')
#define MP4_soun FOURCC('s', 'o', 'u', 'n')
#define MP4_stbl FOURCC('s', 't', 'b', 'l')
#define MP4_stsd FOURCC('s', 't', 's', 'd')
#define MP4_stts FOURCC('s', 't', 't', 's')
#define MP4_trak FOURCC('t', 'r', 'a', 'k')
#define MP4_trkn FOURCC('t', 'r', 'k', 'n')
#define MP4_udta FOURCC('u', 'd', 't', 'a')
#define MP4_extra FOURCC('-', '-', '-', '-')

/* Read the tag data from an MP4 file, storing up to buffer_size bytes in
 * buffer.
 */
static unsigned long read_mp4_tag(int fd, unsigned int size_left, char* buffer,
                                  unsigned int buffer_left)
{
    unsigned int bytes_read = 0;
    
    if (buffer_left == 0)
    {
        lseek(fd, size_left, SEEK_CUR);     /* Skip everything */
    } 
    else 
    {
        /* Skip the data tag header - maybe we should parse it properly? */
        lseek(fd, 16, SEEK_CUR); 
        size_left -= 16;

        if (size_left > buffer_left)
        {
            read(fd, buffer, buffer_left);
            lseek(fd, size_left - buffer_left, SEEK_CUR);
            bytes_read = buffer_left;
        } 
        else
        {
            read(fd, buffer, size_left);
            bytes_read = size_left;
        }
    }
    
    return bytes_read;
}

/* Read a string tag from an MP4 file */
static unsigned int read_mp4_tag_string(int fd, int size_left, char** buffer,
                                        unsigned int* buffer_left, char** dest)
{
    unsigned int bytes_read = read_mp4_tag(fd, size_left, *buffer,
        *buffer_left > 0 ? *buffer_left - 1 : 0);
    unsigned int length = 0;

    if (bytes_read)
    {
        (*buffer)[bytes_read] = 0;
        *dest = *buffer;
        length = strlen(*buffer) + 1;
        *buffer_left -= length;
        *buffer += length;
    }
    else
    {
        *dest = NULL;
    }
    
    return length;
}

static unsigned int read_mp4_atom(int fd, uint32_t* size, 
                                  uint32_t* type, uint32_t size_left)
{
    read_uint32be(fd, size);
    read_uint32be(fd, type);

    if (*size == 1)
    {
        /* FAT32 doesn't support files this big, so something seems to 
         * be wrong. (64-bit sizes should only be used when required.)
         */
        errno = EFBIG;
        *type = 0;
        return 0;
    }

    if (*size > 0)
    {
        if (*size > size_left)
        {
            size_left = 0;
        }
        else
        {
            size_left -= *size;
        }
        
        *size -= 8;
    }
    else
    {
        *size = size_left;
        size_left = 0;
    }
    
    return size_left;
}

static unsigned int read_mp4_length(int fd, uint32_t* size)
{
    unsigned int length = 0;
    int bytes = 0;
    unsigned char c;

    do
    {
        read(fd, &c, 1);
        bytes++;
        (*size)--;
        length = (length << 7) | (c & 0x7F);
    }
    while ((c & 0x80) && (bytes < 4) && (*size > 0));

    return length;
}

static bool read_mp4_esds(int fd, struct mp3entry* id3, uint32_t* size)
{
    unsigned char buf[8];
    bool sbr = false;

    lseek(fd, 4, SEEK_CUR);     /* Version and flags. */
    read(fd, buf, 1);           /* Verify ES_DescrTag. */
    *size -= 5;

    if (*buf == 3)
    {
        /* read length */
        if (read_mp4_length(fd, size) < 20)
        {
            return sbr;
        }

        lseek(fd, 3, SEEK_CUR);
        *size -= 3;
    } 
    else
    {
        lseek(fd, 2, SEEK_CUR);
        *size -= 2;
    }

    read(fd, buf, 1);           /* Verify DecoderConfigDescrTab. */
    *size -= 1;

    if (*buf != 4)
    {
        return sbr;
    }

    if (read_mp4_length(fd, size) < 13)
    {
        return sbr;
    }
    
    lseek(fd, 13, SEEK_CUR);    /* Skip audio type, bit rates, etc. */
    read(fd, buf, 1);
    *size -= 14;
    
    if (*buf != 5)              /* Verify DecSpecificInfoTag. */
    {
        return sbr;
    }

    {
        static const int sample_rates[] =
        {
            96000, 88200, 64000, 48000, 44100, 32000,
            24000, 22050, 16000, 12000, 11025, 8000
        };
        unsigned long bits;
        unsigned int length;
        unsigned int index;
        unsigned int type;
        
        /* Read the (leading part of the) decoder config. */
        length = read_mp4_length(fd, size);
        length = MIN(length, *size);
        length = MIN(length, sizeof(buf));
        memset(buf, 0, sizeof(buf));
        read(fd, buf, length);
        *size -= length;
        
        /* Maybe time to write a simple read_bits function... */

        /* Decoder config format:
         * Object type           - 5 bits
         * Frequency index       - 4 bits
         * Channel configuration - 4 bits
         */
        bits = get_long_be(buf);
        type = bits >> 27;              /* Object type - 5 bits */
        index = (bits >> 23) & 0xf;     /* Frequency index - 4 bits */

        if (index < (sizeof(sample_rates) / sizeof(*sample_rates)))
        {
            id3->frequency = sample_rates[index];
        }
    
        if (type == 5)
        {
            unsigned int old_index = index;

            sbr = true;
            index = (bits >> 15) & 0xf; /* Frequency index - 4 bits */
    
            if (index == 15)
            {
                /* 17 bits read so far... */
                bits = get_long_be(&buf[2]);
                id3->frequency = (bits >> 7) & 0x00ffffff;
            }
            else if (index < (sizeof(sample_rates) / sizeof(*sample_rates)))
            {
                id3->frequency = sample_rates[index];
            }
            
            if (old_index == index)
            {
                /* Downsampled SBR */
                id3->frequency *= 2;
            }
        }
        /* Skip 13 bits from above, plus 3 bits, then read 11 bits */
        else if ((length >= 4) && (((bits >> 5) & 0x7ff) == 0x2b7))
        {
            /* We found an extensionAudioObjectType */
            type = bits & 0x1f;         /* Object type - 5 bits*/
            bits = get_long_be(&buf[4]);
            
            if (type == 5)
            {
                sbr = bits >> 31;

                if (sbr)
                {
                    unsigned int old_index = index;
                    
                    /* 1 bit read so far */
                    index = (bits >> 27) & 0xf; /* Frequency index - 4 bits */

                    if (index == 15)
                    {
                        /* 5 bits read so far */
                        id3->frequency = (bits >> 3) & 0x00ffffff;
                    }
                    else if (index < (sizeof(sample_rates) / sizeof(*sample_rates)))
                    {
                        id3->frequency = sample_rates[index];
                    }

                    if (old_index == index)
                    {
                        /* Downsampled SBR */
                        id3->frequency *= 2;
                    }
                }
            }
        }
        
        if (!sbr && (id3->frequency <= 24000) && (length <= 2))
        {
            /* Double the frequency for low-frequency files without a "long" 
             * DecSpecificConfig header. The file may or may not contain SBR,
             * but here we guess it does if the header is short. This can
             * fail on some files, but it's the best we can do, short of 
             * decoding (parts of) the file.
             */
            id3->frequency *= 2;
            sbr = true;
        }
    }
    
    return sbr;
}

static bool read_mp4_tags(int fd, struct mp3entry* id3, 
                          uint32_t size_left)
{
    uint32_t size;
    uint32_t type;
    unsigned int buffer_left = sizeof(id3->id3v2buf) + sizeof(id3->id3v1buf);
    char* buffer = id3->id3v2buf;
    bool cwrt = false;

    do
    {
        size_left = read_mp4_atom(fd, &size, &type, size_left);

        /* DEBUGF("Tag atom: '%c%c%c%c' (%d bytes left)\n", type >> 24 & 0xff, 
            type >> 16 & 0xff, type >> 8 & 0xff, type & 0xff, size); */

        switch (type)
        {
        case MP4_cnam:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left, 
                &id3->title);
            break;

        case MP4_cART:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left, 
                &id3->artist);
            break;

        case MP4_aART:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                &id3->albumartist);
            break;

        case MP4_cgrp:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                &id3->grouping);
            break;
        
        case MP4_calb:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                &id3->album);
            break;
        
        case MP4_cwrt:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                &id3->composer);
            cwrt = false;
            break;

        case MP4_ccmt:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                &id3->comment);
            break;

        case MP4_cday:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                                &id3->year_string);
 
            /* Try to parse it as a year, for the benefit of the database.
             */
            if(id3->year_string)
            {
                id3->year = atoi(id3->year_string);
                if (id3->year < 1900)
                {
                    id3->year = 0;
                }
            }
            else
                id3->year = 0;

            break;

        case MP4_gnre:
            {
                unsigned short genre;
                
                read_mp4_tag(fd, size, (char*) &genre, sizeof(genre));
                id3->genre_string = id3_get_num_genre(betoh16(genre) - 1);
            }
            break;
        
        case MP4_cgen:
            read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                &id3->genre_string);
            break;

        case MP4_disk:
            {
                unsigned short n[2];
                
                read_mp4_tag(fd, size, (char*) &n, sizeof(n));
                id3->discnum = betoh16(n[1]);
            }
            break;

        case MP4_trkn:
            {
                unsigned short n[2];
                
                read_mp4_tag(fd, size, (char*) &n, sizeof(n));
                id3->tracknum = betoh16(n[1]);
            }
            break;

        case MP4_extra:
            {
                char tag_name[TAG_NAME_LENGTH];
                uint32_t sub_size;
                
                /* "mean" atom */
                read_uint32be(fd, &sub_size);
                size -= sub_size;
                lseek(fd, sub_size - 4, SEEK_CUR);
                /* "name" atom */
                read_uint32be(fd, &sub_size);
                size -= sub_size;
                lseek(fd, 8, SEEK_CUR);
                sub_size -= 12;
                
                if (sub_size > sizeof(tag_name) - 1)
                {
                    read(fd, tag_name, sizeof(tag_name) - 1);
                    lseek(fd, sub_size - (sizeof(tag_name) - 1), SEEK_CUR);
                    tag_name[sizeof(tag_name) - 1] = 0;
                }
                else
                {
                    read(fd, tag_name, sub_size);
                    tag_name[sub_size] = 0;
                }
                
                if ((strcasecmp(tag_name, "composer") == 0) && !cwrt)
                {
                    read_mp4_tag_string(fd, size, &buffer, &buffer_left, 
                        &id3->composer);
                }   
                else if (strcasecmp(tag_name, "iTunSMPB") == 0)
                {
                    char value[TAG_VALUE_LENGTH];
                    char* value_p = value;
                    char* any;
                    unsigned int length = sizeof(value);

                    read_mp4_tag_string(fd, size, &value_p, &length, &any);
                    id3->lead_trim = get_itunes_int32(value, 1);
                    id3->tail_trim = get_itunes_int32(value, 2);
                    DEBUGF("AAC: lead_trim %d, tail_trim %d\n", 
                        id3->lead_trim, id3->tail_trim);
                }
                else if (strcasecmp(tag_name, "musicbrainz track id") == 0)
                {
                    read_mp4_tag_string(fd, size, &buffer, &buffer_left,
                        &id3->mb_track_id);
                }
                else if ((strcasecmp(tag_name, "album artist") == 0))
                {
                    read_mp4_tag_string(fd, size, &buffer, &buffer_left, 
                        &id3->albumartist);
                }   
                else
                {
                    char* any;
                    unsigned int length = read_mp4_tag_string(fd, size,
                        &buffer, &buffer_left, &any);
                    
                    if (length > 0)
                    {
                        /* Re-use the read buffer as the dest buffer... */
                        buffer -= length;
                        buffer_left += length;
                        
                        if (parse_replaygain(tag_name, buffer, id3, 
                            buffer, buffer_left) > 0)
                        {
                            /* Data used, keep it. */
                            buffer += length;
                            buffer_left -= length;
                        }
                    }
                }
            }
            break;
        
        default:
            lseek(fd, size, SEEK_CUR);
            break;
        }
    }
    while ((size_left > 0) && (errno == 0));

    return true;
}

static bool read_mp4_container(int fd, struct mp3entry* id3, 
                               uint32_t size_left)
{
    uint32_t size    = 0;
    uint32_t type    = 0;
    uint32_t handler = 0;
    bool rc = true;
    bool done = false;
    
    do
    {
        size_left = read_mp4_atom(fd, &size, &type, size_left);
        
        /* DEBUGF("Atom: '%c%c%c%c' (0x%08lx, %lu bytes left)\n", 
            (int) ((type >> 24) & 0xff), (int) ((type >> 16) & 0xff),
            (int) ((type >> 8) & 0xff), (int) (type & 0xff),
            type, size); */
        
        switch (type)
        {
        case MP4_ftyp:
            {
                uint32_t id;
                
                read_uint32be(fd, &id);
                size -= 4;
                
                if ((id != MP4_M4A) && (id != MP4_M4B) && (id != MP4_mp42) 
                    && (id != MP4_qt) && (id != MP4_3gp6) && (id != MP4_m4a)
                    && (id != MP4_isom))
                {
                    DEBUGF("Unknown MP4 file type: '%c%c%c%c'\n", 
                        (int)(id >> 24 & 0xff), (int)(id >> 16 & 0xff),
                        (int)(id >> 8 & 0xff), (int)(id & 0xff));
                    return false;
                }
            }
            break;

        case MP4_meta:
            lseek(fd, 4, SEEK_CUR);  /* Skip version */
            size -= 4;
            /* Fall through */

        case MP4_moov:
        case MP4_udta:
        case MP4_mdia:
        case MP4_stbl:
        case MP4_trak:
            rc = read_mp4_container(fd, id3, size);
            size = 0;
            break;
        
        case MP4_ilst:
            /* We need at least a size of 8 to read the next atom. */
            if (handler == MP4_mdir && size>8)
            {
                rc = read_mp4_tags(fd, id3, size);
                size = 0;
            }
            break;
        
        case MP4_minf:
            if (handler == MP4_soun)
            {
                rc = read_mp4_container(fd, id3, size);
                size = 0;
            }
            break;
        
        case MP4_stsd:
            lseek(fd, 8, SEEK_CUR);
            size -= 8;
            rc = read_mp4_container(fd, id3, size);
            size = 0;
            break;
        
        case MP4_hdlr:
            lseek(fd, 8, SEEK_CUR);
            read_uint32be(fd, &handler);
            size -= 12;
            /* DEBUGF("    Handler '%c%c%c%c'\n", handler >> 24 & 0xff, 
                handler >> 16 & 0xff, handler >> 8 & 0xff,handler & 0xff); */
            break;
        
        case MP4_stts:
            {
                uint32_t entries;
                unsigned int i;

                /* Reset to false. */
                id3->needs_upsampling_correction = false;

                lseek(fd, 4, SEEK_CUR);
                read_uint32be(fd, &entries);
                id3->samples = 0;

                for (i = 0; i < entries; i++)
                {
                    uint32_t n;
                    uint32_t l;

                    read_uint32be(fd, &n);
                    read_uint32be(fd, &l);

                    /* Some AAC file use HE profile. In this case the number
                     * of output samples is doubled to a maximum of 2048 
                     * samples per frame. This means that files which already 
                     * report a frame size of 2048 in their header will not 
                     * need any further special handling. */
                    if (id3->codectype==AFMT_MP4_AAC_HE && l<=1024)
                    {
                        id3->samples += n * l * 2;
                        id3->needs_upsampling_correction = true;
                    }
                    else
                    {
                        id3->samples += n * l;
                    }
                }
                
                size = 0;
            }
            break;

        case MP4_mp4a:
            {
                uint32_t subsize;
                uint32_t subtype;

                /* Move to the next expected mp4 atom. */
                lseek(fd, 28, SEEK_CUR);
                read_mp4_atom(fd, &subsize, &subtype, size);
                size -= 36;

                if (subtype == MP4_esds)
                {
                    /* Read esds metadata and return if AAC-HE/SBR is used. */
                    if (read_mp4_esds(fd, id3, &size))
                        id3->codectype = AFMT_MP4_AAC_HE;
                    else
                        id3->codectype = AFMT_MP4_AAC;
                }
            }
            break;

        case MP4_alac:
            {
                uint32_t frequency;
                uint32_t subsize;
                uint32_t subtype;

                /* Move to the next expected mp4 atom. */
                lseek(fd, 28, SEEK_CUR);
                read_mp4_atom(fd, &subsize, &subtype, size);
                size -= 36;
#if 0
                /* We might need to parse for the alac metadata atom. */
                while (!((subsize==28) && (subtype==MP4_alac)) && (size>0))
                {
                    lseek(fd, -7, SEEK_CUR);
                    read_mp4_atom(fd, &subsize, &subtype, size);
                    size -= 1;
                    errno = 0; /* will most likely be set while parsing */
                }
#endif
                if (subtype == MP4_alac)
                {
                    lseek(fd, 24, SEEK_CUR);
                    read_uint32be(fd, &frequency);
                    size -= 28;
                    id3->frequency = frequency;
                    id3->codectype = AFMT_MP4_ALAC;
                }
            }
            break;

        case MP4_mdat:
            /* Some AAC files appear to contain additional empty mdat chunks.
               Ignore them. */
            if(size == 0)
                break;
            id3->filesize = size;
            if(id3->samples > 0) {
                /* We've already seen the moov chunk. */
                done = true;
            }
            break;

        case MP4_chpl:
            {
                /* ADDME: add support for real chapters. Right now it's only
                 * used for Nero's gapless hack */
                uint8_t chapters;
                uint64_t timestamp;

                lseek(fd, 8, SEEK_CUR);
                read_uint8(fd, &chapters);
                size -= 9;

                /* the first chapter will be used as the lead_trim */
                if (chapters > 0) {
                    read_uint64be(fd, &timestamp);
                    id3->lead_trim = (timestamp * id3->frequency) / 10000000;
                    size -= 8;
                }
            }
            break;

        default:
            break;
        }
        
        /* Skip final seek. */
        if (!done)
        {
            lseek(fd, size, SEEK_CUR);
        }
    } while (rc && (size_left > 0) && (errno == 0) && !done);
    
    return rc;
}

bool get_mp4_metadata(int fd, struct mp3entry* id3)
{
    id3->codectype = AFMT_UNKNOWN;
    id3->filesize = 0;
    errno = 0;

    if (read_mp4_container(fd, id3, filesize(fd)) && (errno == 0) 
        && (id3->samples > 0) && (id3->frequency > 0) 
        && (id3->filesize > 0))
    {
        if (id3->codectype == AFMT_UNKNOWN)
        {
            logf("Not an ALAC or AAC file");
            return false;
        }

        id3->length = ((int64_t) id3->samples * 1000) / id3->frequency;

        id3->vbr = true; /* ALAC is native VBR, AAC very unlikely is CBR. */

        if (id3->length <= 0)
        {
            logf("mp4 length invalid!");
            return false;
        }

        id3->bitrate = ((int64_t) id3->filesize * 8) / id3->length;
        DEBUGF("MP4 bitrate %d, frequency %ld Hz, length %ld ms\n",
            id3->bitrate, id3->frequency, id3->length);
    }
    else
    {
        logf("MP4 metadata error");
        DEBUGF("MP4 metadata error. errno %d, samples %ld, frequency %ld, "
            "filesize %ld\n", errno, id3->samples, id3->frequency,
            id3->filesize);
        return false;
    }

    return true;
}