libavformat/aadec.c

   1 /*
   2  * Audible AA demuxer
   3  * Copyright (c) 2015 Vesselin Bontchev
   4  *
   5  * Header parsing is borrowed from https://github.com/jteeuwen/audible project.
   6  * Copyright (c) 2001-2014, Jim Teeuwen
   7  *
   8  * Redistribution and use in source and binary forms, with or without modification,
   9  * are permitted provided that the following conditions are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright notice, this
  12  *    list of conditions and the following disclaimer.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  16  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  17  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
  18  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  19  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  20  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
  21  * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  23  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "avformat.h"
  27 #include "demux.h"
  28 #include "internal.h"
  29 #include "libavutil/avstring.h"
  30 #include "libavutil/dict.h"
  31 #include "libavutil/intreadwrite.h"
  32 #include "libavutil/mem.h"
  33 #include "libavutil/tea.h"
  34 #include "libavutil/opt.h"
  35
  36 #define AA_MAGIC 1469084982 /* this identifies an audible .aa file */
  37 #define MAX_TOC_ENTRIES 16
  38 #define MAX_DICTIONARY_ENTRIES 128
  39 #define TEA_BLOCK_SIZE 8
  40 #define CHAPTER_HEADER_SIZE 8
  41 #define TIMEPREC 1000
  42 #define MP3_FRAME_SIZE 104
  43
  44 typedef struct AADemuxContext {
  45     AVClass *class;
  46     uint8_t *aa_fixed_key;
  47     int aa_fixed_key_len;
  48     int codec_second_size;
  49     int current_codec_second_size;
  50     int chapter_idx;
  51     struct AVTEA *tea_ctx;
  52     uint8_t file_key[16];
  53     int64_t current_chapter_size;
  54     int64_t content_start;
  55     int64_t content_end;
  56     int seek_offset;
  57 } AADemuxContext;
  58
  59 static int get_second_size(char *codec_name)
  60 {
  61     int result = -1;
  62
  63     if (!strcmp(codec_name, "mp332")) {
  64         result = 3982;
  65     } else if (!strcmp(codec_name, "acelp16")) {
  66         result = 2000;
  67     } else if (!strcmp(codec_name, "acelp85")) {
  68         result = 1045;
  69     }
  70
  71     return result;
  72 }
  73
  74 static int aa_read_header(AVFormatContext *s)
  75 {
  76     int largest_idx = -1;
  77     uint32_t toc_size, npairs, header_seed = 0, start;
  78     char codec_name[64] = {0};
  79     uint8_t buf[24];
  80     int64_t largest_size = -1, current_size = -1, chapter_pos;
  81     struct toc_entry {
  82         uint32_t offset;
  83         uint32_t size;
  84     } TOC[MAX_TOC_ENTRIES];
  85     uint8_t header_key[16] = {0};
  86     AADemuxContext *c = s->priv_data;
  87     char file_key[2 * sizeof(c->file_key) + 1];
  88     AVIOContext *pb = s->pb;
  89     AVStream *st;
  90     FFStream *sti;
  91     int ret;
  92
  93     /* parse .aa header */
  94     avio_skip(pb, 4); // file size
  95     avio_skip(pb, 4); // magic string
  96     toc_size = avio_rb32(pb); // TOC size
  97     avio_skip(pb, 4); // unidentified integer
  98     if (toc_size > MAX_TOC_ENTRIES || toc_size < 2)
  99         return AVERROR_INVALIDDATA;
 100     for (uint32_t i = 0; i < toc_size; i++) { // read TOC
 101         avio_skip(pb, 4); // TOC entry index
 102         TOC[i].offset = avio_rb32(pb); // block offset
 103         TOC[i].size = avio_rb32(pb); // block size
 104     }
 105     avio_skip(pb, 24); // header termination block (ignored)
 106     npairs = avio_rb32(pb); // read dictionary entries
 107     if (npairs > MAX_DICTIONARY_ENTRIES)
 108         return AVERROR_INVALIDDATA;
 109     for (uint32_t i = 0; i < npairs; i++) {
 110         char key[128], val[128];
 111         uint32_t nkey, nval;
 112
 113         avio_skip(pb, 1); // unidentified integer
 114         nkey = avio_rb32(pb); // key string length
 115         nval = avio_rb32(pb); // value string length
 116         avio_get_str(pb, nkey, key, sizeof(key));
 117         avio_get_str(pb, nval, val, sizeof(val));
 118         if (!strcmp(key, "codec")) {
 119             av_log(s, AV_LOG_DEBUG, "Codec is <%s>\n", val);
 120             av_strlcpy(codec_name, val, sizeof(codec_name));
 121         } else if (!strcmp(key, "HeaderSeed")) {
 122             av_log(s, AV_LOG_DEBUG, "HeaderSeed is <%s>\n", val);
 123             header_seed = atoi(val);
 124         } else if (!strcmp(key, "HeaderKey")) { // this looks like "1234567890 1234567890 1234567890 1234567890"
 125             uint32_t header_key_part[4];
 126             av_log(s, AV_LOG_DEBUG, "HeaderKey is <%s>\n", val);
 127
 128             ret = sscanf(val, "%"SCNu32"%"SCNu32"%"SCNu32"%"SCNu32,
 129                    &header_key_part[0], &header_key_part[1], &header_key_part[2], &header_key_part[3]);
 130             if (ret != 4)
 131                 return AVERROR_INVALIDDATA;
 132
 133             for (int idx = 0; idx < 4; idx++)
 134                 AV_WB32(&header_key[idx * 4], header_key_part[idx]); // convert each part to BE!
 135             ff_data_to_hex(key, header_key, sizeof(header_key), 1);
 136             av_log(s, AV_LOG_DEBUG, "Processed HeaderKey is %s\n", key);
 137         } else {
 138             av_dict_set(&s->metadata, key, val, 0);
 139         }
 140     }
 141
 142     /* verify fixed key */
 143     if (c->aa_fixed_key_len != 16) {
 144         av_log(s, AV_LOG_ERROR, "aa_fixed_key value needs to be 16 bytes!\n");
 145         return AVERROR(EINVAL);
 146     }
 147
 148     /* verify codec */
 149     if ((c->codec_second_size = get_second_size(codec_name)) == -1) {
 150         av_log(s, AV_LOG_ERROR, "unknown codec <%s>!\n", codec_name);
 151         return AVERROR(EINVAL);
 152     }
 153
 154     /* decryption key derivation */
 155     c->tea_ctx = av_tea_alloc();
 156     if (!c->tea_ctx)
 157         return AVERROR(ENOMEM);
 158     av_tea_init(c->tea_ctx, c->aa_fixed_key, 16);
 159     for (int i = 0; i < 6; i++)
 160         AV_WB32(buf + 4 * i, header_seed + i);
 161     av_tea_crypt(c->tea_ctx, buf, buf, 3, NULL, 0);
 162     AV_WN64(c->file_key,     AV_RN64(buf + 2)  ^ AV_RN64(header_key));
 163     AV_WN64(c->file_key + 8, AV_RN64(buf + 10) ^ AV_RN64(header_key + 8));
 164     ff_data_to_hex(file_key, c->file_key, sizeof(c->file_key), 1);
 165     av_log(s, AV_LOG_DEBUG, "File key is %s\n", file_key);
 166     av_tea_init(c->tea_ctx, c->file_key, 16);
 167
 168     /* decoder setup */
 169     st = avformat_new_stream(s, NULL);
 170     if (!st)
 171         return AVERROR(ENOMEM);
 172     sti = ffstream(st);
 173     st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
 174     if (!strcmp(codec_name, "mp332")) {
 175         st->codecpar->codec_id = AV_CODEC_ID_MP3;
 176         st->codecpar->sample_rate = 22050;
 177         sti->need_parsing = AVSTREAM_PARSE_FULL_RAW;
 178         avpriv_set_pts_info(st, 64, 8, 32000 * TIMEPREC);
 179         // encoded audio frame is MP3_FRAME_SIZE bytes (+1 with padding, unlikely)
 180     } else if (!strcmp(codec_name, "acelp85")) {
 181         st->codecpar->codec_id = AV_CODEC_ID_SIPR;
 182         st->codecpar->block_align = 19;
 183         st->codecpar->ch_layout.nb_channels = 1;
 184         st->codecpar->sample_rate = 8500;
 185         st->codecpar->bit_rate = 8500;
 186         sti->need_parsing = AVSTREAM_PARSE_FULL_RAW;
 187         avpriv_set_pts_info(st, 64, 8, 8500 * TIMEPREC);
 188     } else if (!strcmp(codec_name, "acelp16")) {
 189         st->codecpar->codec_id = AV_CODEC_ID_SIPR;
 190         st->codecpar->block_align = 20;
 191         st->codecpar->ch_layout.nb_channels = 1;
 192         st->codecpar->sample_rate = 16000;
 193         st->codecpar->bit_rate = 16000;
 194         sti->need_parsing = AVSTREAM_PARSE_FULL_RAW;
 195         avpriv_set_pts_info(st, 64, 8, 16000 * TIMEPREC);
 196     }
 197
 198     /* determine, and jump to audio start offset */
 199     for (uint32_t i = 1; i < toc_size; i++) { // skip the first entry!
 200         current_size = TOC[i].size;
 201         if (current_size > largest_size) {
 202             largest_idx = i;
 203             largest_size = current_size;
 204         }
 205     }
 206     start = TOC[largest_idx].offset;
 207     avio_seek(pb, start, SEEK_SET);
 208
 209     // extract chapter positions. since all formats have constant bit rate, use it
 210     // as time base in bytes/s, for easy stream position <-> timestamp conversion
 211     st->start_time = 0;
 212     c->content_start = start;
 213     c->content_end = start + largest_size;
 214
 215     while ((chapter_pos = avio_tell(pb)) >= 0 && chapter_pos < c->content_end) {
 216         unsigned chapter_idx = s->nb_chapters;
 217         uint32_t chapter_size = avio_rb32(pb);
 218         if (chapter_size == 0 || avio_feof(pb))
 219             break;
 220         chapter_pos -= start + CHAPTER_HEADER_SIZE * chapter_idx;
 221         avio_skip(pb, 4 + chapter_size);
 222         if (!avpriv_new_chapter(s, chapter_idx, st->time_base,
 223                                 chapter_pos * TIMEPREC,
 224                                 (chapter_pos + chapter_size) * TIMEPREC, NULL))
 225             return AVERROR(ENOMEM);
 226     }
 227
 228     st->duration = (largest_size - CHAPTER_HEADER_SIZE * s->nb_chapters) * TIMEPREC;
 229
 230     avpriv_update_cur_dts(s, st, 0);
 231     avio_seek(pb, start, SEEK_SET);
 232     c->current_chapter_size = 0;
 233     c->seek_offset = 0;
 234
 235     return 0;
 236 }
 237
 238 static int aa_read_packet(AVFormatContext *s, AVPacket *pkt)
 239 {
 240     int ret;
 241     AADemuxContext *c = s->priv_data;
 242     uint64_t pos = avio_tell(s->pb);
 243
 244     // are we at the end of the audio content?
 245     if (pos >= c->content_end) {
 246         return AVERROR_EOF;
 247     }
 248
 249     // are we at the start of a chapter?
 250     if (c->current_chapter_size == 0) {
 251         c->current_chapter_size = avio_rb32(s->pb);
 252         if (c->current_chapter_size == 0) {
 253             return AVERROR_EOF;
 254         }
 255         av_log(s, AV_LOG_DEBUG, "Chapter %d (%" PRId64 " bytes)\n", c->chapter_idx, c->current_chapter_size);
 256         c->chapter_idx = c->chapter_idx + 1;
 257         avio_skip(s->pb, 4); // data start offset
 258         c->current_codec_second_size = c->codec_second_size;
 259     }
 260
 261     // is this the last block in this chapter?
 262     if (c->current_chapter_size / c->current_codec_second_size == 0) {
 263         c->current_codec_second_size = c->current_chapter_size % c->current_codec_second_size;
 264     }
 265
 266     ret = av_get_packet(s->pb, pkt, c->current_codec_second_size);
 267     if (ret != c->current_codec_second_size)
 268         return AVERROR_EOF;
 269
 270     // decrypt c->current_codec_second_size bytes in blocks of TEA_BLOCK_SIZE
 271     // trailing bytes are left unencrypted!
 272     av_tea_crypt(c->tea_ctx, pkt->data, pkt->data,
 273                  c->current_codec_second_size / TEA_BLOCK_SIZE, NULL, 1);
 274
 275     // update state
 276     c->current_chapter_size = c->current_chapter_size - c->current_codec_second_size;
 277     if (c->current_chapter_size <= 0)
 278         c->current_chapter_size = 0;
 279
 280     if (c->seek_offset > c->current_codec_second_size)
 281         c->seek_offset = 0; // ignore wrong estimate
 282     pkt->data += c->seek_offset;
 283     pkt->size -= c->seek_offset;
 284     c->seek_offset = 0;
 285
 286     return 0;
 287 }
 288
 289 static int aa_read_seek(AVFormatContext *s,
 290                         int stream_index, int64_t timestamp, int flags)
 291 {
 292     AADemuxContext *c = s->priv_data;
 293     AVChapter *ch;
 294     int64_t chapter_pos, chapter_start, chapter_size;
 295     int chapter_idx = 0;
 296
 297     // find chapter containing seek timestamp
 298     if (timestamp < 0)
 299         timestamp = 0;
 300
 301     while (chapter_idx < s->nb_chapters && timestamp >= s->chapters[chapter_idx]->end) {
 302         ++chapter_idx;
 303     }
 304
 305     if (chapter_idx >= s->nb_chapters) {
 306         chapter_idx = s->nb_chapters - 1;
 307         if (chapter_idx < 0) return -1; // there is no chapter.
 308         timestamp = s->chapters[chapter_idx]->end;
 309     }
 310
 311     ch = s->chapters[chapter_idx];
 312
 313     // sync by clamping timestamp to nearest valid block position in its chapter
 314     chapter_size = ch->end / TIMEPREC - ch->start / TIMEPREC;
 315     chapter_pos = av_rescale_rnd((timestamp - ch->start) / TIMEPREC,
 316         1, c->codec_second_size,
 317         (flags & AVSEEK_FLAG_BACKWARD) ? AV_ROUND_DOWN : AV_ROUND_UP)
 318         * c->codec_second_size;
 319     if (chapter_pos >= chapter_size)
 320         chapter_pos = chapter_size;
 321     chapter_start = c->content_start + (ch->start / TIMEPREC) + CHAPTER_HEADER_SIZE * (1 + chapter_idx);
 322
 323     // reinit read state
 324     avio_seek(s->pb, chapter_start + chapter_pos, SEEK_SET);
 325     c->current_codec_second_size = c->codec_second_size;
 326     c->current_chapter_size = chapter_size - chapter_pos;
 327     c->chapter_idx = 1 + chapter_idx;
 328
 329     // for unaligned frames, estimate offset of first frame in block (assume no padding)
 330     if (s->streams[0]->codecpar->codec_id == AV_CODEC_ID_MP3) {
 331         c->seek_offset = (MP3_FRAME_SIZE - chapter_pos % MP3_FRAME_SIZE) % MP3_FRAME_SIZE;
 332     }
 333
 334     avpriv_update_cur_dts(s, s->streams[0], ch->start + (chapter_pos + c->seek_offset) * TIMEPREC);
 335
 336     return 1;
 337 }
 338
 339 static int aa_probe(const AVProbeData *p)
 340 {
 341     uint8_t *buf = p->buf;
 342
 343     // first 4 bytes are file size, next 4 bytes are the magic
 344     if (AV_RB32(buf+4) != AA_MAGIC)
 345         return 0;
 346
 347     return AVPROBE_SCORE_MAX / 2;
 348 }
 349
 350 static int aa_read_close(AVFormatContext *s)
 351 {
 352     AADemuxContext *c = s->priv_data;
 353
 354     av_freep(&c->tea_ctx);
 355
 356     return 0;
 357 }
 358
 359 #define OFFSET(x) offsetof(AADemuxContext, x)
 360 static const AVOption aa_options[] = {
 361     { "aa_fixed_key", // extracted from libAAX_SDK.so and AAXSDKWin.dll files!
 362         "Fixed key used for handling Audible AA files", OFFSET(aa_fixed_key),
 363         AV_OPT_TYPE_BINARY, {.str="77214d4b196a87cd520045fd2a51d673"},
 364         .flags = AV_OPT_FLAG_DECODING_PARAM },
 365     { NULL },
 366 };
 367
 368 static const AVClass aa_class = {
 369     .class_name = "aa",
 370     .item_name  = av_default_item_name,
 371     .option     = aa_options,
 372     .version    = LIBAVUTIL_VERSION_INT,
 373 };
 374
 375 const FFInputFormat ff_aa_demuxer = {
 376     .p.name         = "aa",
 377     .p.long_name    = NULL_IF_CONFIG_SMALL("Audible AA format files"),
 378     .p.priv_class   = &aa_class,
 379     .p.extensions   = "aa",
 380     .p.flags        = AVFMT_NO_BYTE_SEEK | AVFMT_NOGENSEARCH,
 381     .priv_data_size = sizeof(AADemuxContext),
 382     .read_probe     = aa_probe,
 383     .read_header    = aa_read_header,
 384     .read_packet    = aa_read_packet,
 385     .read_seek      = aa_read_seek,
 386     .read_close     = aa_read_close,
 387     .flags_internal = FF_INFMT_FLAG_INIT_CLEANUP,
 388 };