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  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 "internal.h"
  28. #include "libavutil/intreadwrite.h"
  29. #include "libavutil/tea.h"
  30. #include "libavutil/opt.h"
  31.  
  32. #define AA_MAGIC 1469084982 /* this identifies an audible .aa file */
  33. #define MAX_CODEC_SECOND_SIZE 3982
  34. #define MAX_TOC_ENTRIES 16
  35. #define MAX_DICTIONARY_ENTRIES 128
  36. #define TEA_BLOCK_SIZE 8
  37.  
  38. typedef struct AADemuxContext {
  39.     AVClass *class;
  40.     uint8_t *aa_fixed_key;
  41.     int aa_fixed_key_len;
  42.     int codec_second_size;
  43.     int current_codec_second_size;
  44.     int chapter_idx;
  45.     struct AVTEA *tea_ctx;
  46.     uint8_t file_key[16];
  47.     int64_t current_chapter_size;
  48. } AADemuxContext;
  49.  
  50. static int get_second_size(char *codec_name)
  51. {
  52.     int result = -1;
  53.  
  54.     if (!strcmp(codec_name, "mp332")) {
  55.         result = 3982;
  56.     } else if (!strcmp(codec_name, "acelp16")) {
  57.         result = 2000;
  58.     } else if (!strcmp(codec_name, "acelp85")) {
  59.         result = 1045;
  60.     }
  61.  
  62.     return result;
  63. }
  64.  
  65. static int aa_read_header(AVFormatContext *s)
  66. {
  67.     int i, j, idx, largest_idx = -1;
  68.     uint32_t nkey, nval, toc_size, npairs, header_seed, start;
  69.     char key[128], val[128], codec_name[64] = {0};
  70.     uint8_t output[24], dst[8], src[8];
  71.     int64_t largest_size = -1, current_size = -1;
  72.     struct toc_entry {
  73.         uint32_t offset;
  74.         uint32_t size;
  75.     } TOC[MAX_TOC_ENTRIES];
  76.     uint32_t header_key_part[4];
  77.     uint8_t header_key[16];
  78.     AADemuxContext *c = s->priv_data;
  79.     AVIOContext *pb = s->pb;
  80.     AVStream *st;
  81.  
  82.     /* parse .aa header */
  83.     avio_skip(pb, 4); // file size
  84.     avio_skip(pb, 4); // magic string
  85.     toc_size = avio_rb32(pb); // TOC size
  86.     avio_skip(pb, 4); // unidentified integer
  87.     if (toc_size > MAX_TOC_ENTRIES)
  88.         return AVERROR_INVALIDDATA;
  89.     for (i = 0; i < toc_size; i++) { // read TOC
  90.         avio_skip(pb, 4); // TOC entry index
  91.         TOC[i].offset = avio_rb32(pb); // block offset
  92.         TOC[i].size = avio_rb32(pb); // block size
  93.     }
  94.     avio_skip(pb, 24); // header termination block (ignored)
  95.     npairs = avio_rb32(pb); // read dictionary entries
  96.     if (npairs > MAX_DICTIONARY_ENTRIES)
  97.         return AVERROR_INVALIDDATA;
  98.     for (i = 0; i < npairs; i++) {
  99.         memset(val, 0, sizeof(val));
  100.         memset(key, 0, sizeof(key));
  101.         avio_skip(pb, 1); // unidentified integer
  102.         nkey = avio_rb32(pb); // key string length
  103.         nval = avio_rb32(pb); // value string length
  104.         if (nkey > sizeof(key)) {
  105.             avio_skip(pb, nkey);
  106.         } else {
  107.             avio_read(pb, key, nkey); // key string
  108.         }
  109.         if (nval > sizeof(val)) {
  110.             avio_skip(pb, nval);
  111.         } else {
  112.             avio_read(pb, val, nval); // value string
  113.         }
  114.         if (!strcmp(key, "codec")) {
  115.             av_log(s, AV_LOG_DEBUG, "Codec is <%s>\n", val);
  116.             strncpy(codec_name, val, sizeof(codec_name) - 1);
  117.         }
  118.         if (!strcmp(key, "HeaderSeed")) {
  119.             av_log(s, AV_LOG_DEBUG, "HeaderSeed is <%s>\n", val);
  120.             header_seed = atoi(val);
  121.         }
  122.         if (!strcmp(key, "HeaderKey")) { // this looks like "1234567890 1234567890 1234567890 1234567890"
  123.             av_log(s, AV_LOG_DEBUG, "HeaderKey is <%s>\n", val);
  124.             sscanf(val, "%u%u%u%u", &header_key_part[0], &header_key_part[1], &header_key_part[2], &header_key_part[3]);
  125.             for (idx = 0; idx < 4; idx++) {
  126.                 AV_WB32(&header_key[idx * 4], header_key_part[idx]); // convert each part to BE!
  127.             }
  128.             av_log(s, AV_LOG_DEBUG, "Processed HeaderKey is ");
  129.             for (i = 0; i < 16; i++)
  130.                 av_log(s, AV_LOG_DEBUG, "%02x", header_key[i]);
  131.             av_log(s, AV_LOG_DEBUG, "\n");
  132.         }
  133.     }
  134.  
  135.     /* verify fixed key */
  136.     if (c->aa_fixed_key_len != 16) {
  137.         av_log(s, AV_LOG_ERROR, "aa_fixed_key value needs to be 16 bytes!\n");
  138.         return AVERROR(EINVAL);
  139.     }
  140.  
  141.     /* verify codec */
  142.     if ((c->codec_second_size = get_second_size(codec_name)) == -1) {
  143.         av_log(s, AV_LOG_ERROR, "unknown codec <%s>!\n", codec_name);
  144.         return AVERROR(EINVAL);
  145.     }
  146.  
  147.     /* decryption key derivation */
  148.     c->tea_ctx = av_tea_alloc();
  149.     if (!c->tea_ctx)
  150.         return AVERROR(ENOMEM);
  151.     av_tea_init(c->tea_ctx, c->aa_fixed_key, 16);
  152.     output[0] = output[1] = 0; // purely for padding purposes
  153.     memcpy(output + 2, header_key, 16);
  154.     idx = 0;
  155.     for (i = 0; i < 3; i++) { // TEA CBC with weird mixed endianness
  156.         AV_WB32(src, header_seed);
  157.         AV_WB32(src + 4, header_seed + 1);
  158.         header_seed += 2;
  159.         av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 0); // TEA ECB encrypt
  160.         for (j = 0; j < TEA_BLOCK_SIZE && idx < 18; j+=1, idx+=1) {
  161.             output[idx] = output[idx] ^ dst[j];
  162.         }
  163.     }
  164.     memcpy(c->file_key, output + 2, 16); // skip first 2 bytes of output
  165.     av_log(s, AV_LOG_DEBUG, "File key is ");
  166.     for (i = 0; i < 16; i++)
  167.         av_log(s, AV_LOG_DEBUG, "%02x", c->file_key[i]);
  168.     av_log(s, AV_LOG_DEBUG, "\n");
  169.  
  170.     /* decoder setup */
  171.     st = avformat_new_stream(s, NULL);
  172.     if (!st) {
  173.         av_freep(&c->tea_ctx);
  174.         return AVERROR(ENOMEM);
  175.     }
  176.     st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  177.     if (!strcmp(codec_name, "mp332")) {
  178.         st->codec->codec_id = AV_CODEC_ID_MP3;
  179.         st->codec->sample_rate = 22050;
  180.         st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
  181.         st->start_time = 0;
  182.     } else if (!strcmp(codec_name, "acelp85")) {
  183.         st->codec->codec_id = AV_CODEC_ID_SIPR;
  184.         st->codec->block_align = 19;
  185.         st->codec->channels = 1;
  186.         st->codec->sample_rate = 8500;
  187.     } else if (!strcmp(codec_name, "acelp16")) {
  188.         st->codec->codec_id = AV_CODEC_ID_SIPR;
  189.         st->codec->block_align = 20;
  190.         st->codec->channels = 1;
  191.         st->codec->sample_rate = 16000;
  192.     }
  193.  
  194.     /* determine, and jump to audio start offset */
  195.     for (i = 1; i < toc_size; i++) { // skip the first entry!
  196.         current_size = TOC[i].size;
  197.         if (current_size > largest_size) {
  198.             largest_idx = i;
  199.             largest_size = current_size;
  200.         }
  201.     }
  202.     start = TOC[largest_idx].offset;
  203.     avio_seek(pb, start, SEEK_SET);
  204.     c->current_chapter_size = 0;
  205.  
  206.     return 0;
  207. }
  208.  
  209. static int aa_read_packet(AVFormatContext *s, AVPacket *pkt)
  210. {
  211.     uint8_t dst[TEA_BLOCK_SIZE];
  212.     uint8_t src[TEA_BLOCK_SIZE];
  213.     int i;
  214.     int trailing_bytes;
  215.     int blocks;
  216.     uint8_t buf[MAX_CODEC_SECOND_SIZE * 2];
  217.     int written = 0;
  218.     int ret;
  219.     AADemuxContext *c = s->priv_data;
  220.  
  221.     // are we at the start of a chapter?
  222.     if (c->current_chapter_size == 0) {
  223.         c->current_chapter_size = avio_rb32(s->pb);
  224.         if (c->current_chapter_size == 0) {
  225.             return AVERROR_EOF;
  226.         }
  227.         av_log(s, AV_LOG_DEBUG, "Chapter %d (%" PRId64 " bytes)\n", c->chapter_idx, c->current_chapter_size);
  228.         c->chapter_idx = c->chapter_idx + 1;
  229.         avio_skip(s->pb, 4); // data start offset
  230.         c->current_codec_second_size = c->codec_second_size;
  231.     }
  232.  
  233.     // is this the last block in this chapter?
  234.     if (c->current_chapter_size / c->current_codec_second_size == 0) {
  235.         c->current_codec_second_size = c->current_chapter_size % c->current_codec_second_size;
  236.     }
  237.  
  238.     // decrypt c->current_codec_second_size bytes
  239.     blocks = c->current_codec_second_size / TEA_BLOCK_SIZE;
  240.     for (i = 0; i < blocks; i++) {
  241.         avio_read(s->pb, src, TEA_BLOCK_SIZE);
  242.         av_tea_init(c->tea_ctx, c->file_key, 16);
  243.         av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 1);
  244.         memcpy(buf + written, dst, TEA_BLOCK_SIZE);
  245.         written = written + TEA_BLOCK_SIZE;
  246.     }
  247.     trailing_bytes = c->current_codec_second_size % TEA_BLOCK_SIZE;
  248.     if (trailing_bytes != 0) { // trailing bytes are left unencrypted!
  249.         avio_read(s->pb, src, trailing_bytes);
  250.         memcpy(buf + written, src, trailing_bytes);
  251.         written = written + trailing_bytes;
  252.     }
  253.  
  254.     // update state
  255.     c->current_chapter_size = c->current_chapter_size - c->current_codec_second_size;
  256.     if (c->current_chapter_size <= 0)
  257.         c->current_chapter_size = 0;
  258.  
  259.     ret = av_new_packet(pkt, written);
  260.     if (ret < 0)
  261.         return ret;
  262.     memcpy(pkt->data, buf, written);
  263.  
  264.     return 0;
  265. }
  266.  
  267. static int aa_probe(AVProbeData *p)
  268. {
  269.     uint8_t *buf = p->buf;
  270.  
  271.     // first 4 bytes are file size, next 4 bytes are the magic
  272.     if (AV_RB32(buf+4) != AA_MAGIC)
  273.         return 0;
  274.  
  275.     return AVPROBE_SCORE_MAX / 2;
  276. }
  277.  
  278. static int aa_read_close(AVFormatContext *s)
  279. {
  280.     AADemuxContext *c = s->priv_data;
  281.  
  282.     av_freep(&c->tea_ctx);
  283.  
  284.     return 0;
  285. }
  286.  
  287. #define OFFSET(x) offsetof(AADemuxContext, x)
  288. static const AVOption aa_options[] = {
  289.     { "aa_fixed_key", // extracted from libAAX_SDK.so and AAXSDKWin.dll files!
  290.         "Fixed key used for handling Audible AA files", OFFSET(aa_fixed_key),
  291.         AV_OPT_TYPE_BINARY, {.str="77214d4b196a87cd520045fd2a51d673"},
  292.         .flags = AV_OPT_FLAG_DECODING_PARAM },
  293.     { NULL },
  294. };
  295.  
  296. static const AVClass aa_class = {
  297.     .class_name = "aa",
  298.     .item_name  = av_default_item_name,
  299.     .option     = aa_options,
  300.     .version    = LIBAVUTIL_VERSION_INT,
  301. };
  302.  
  303. AVInputFormat ff_aa_demuxer = {
  304.     .name           = "aa",
  305.     .long_name      = NULL_IF_CONFIG_SMALL("Audible AA format files"),
  306.     .priv_class     = &aa_class,
  307.     .priv_data_size = sizeof(AADemuxContext),
  308.     .extensions     = "aa",
  309.     .read_probe     = aa_probe,
  310.     .read_header    = aa_read_header,
  311.     .read_packet    = aa_read_packet,
  312.     .read_close     = aa_read_close,
  313.     .flags          = AVFMT_GENERIC_INDEX,
  314. };
  315.