3 * Copyright (c) 2015 Vesselin Bontchev
5 * Header parsing is borrowed from https://github.com/jteeuwen/audible project.
6 * Copyright (c) 2001-2014, Jim Teeuwen
8 * Redistribution and use in source and binary forms, with or without modification,
9 * are permitted provided that the following conditions are met:
11 * 1. Redistributions of source code must retain the above copyright notice, this
12 * list of conditions and the following disclaimer.
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.
28 #include "libavutil/intreadwrite.h"
29 #include "libavutil/tea.h"
30 #include "libavutil/opt.h"
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
38 typedef struct AADemuxContext {
40 uint8_t *aa_fixed_key;
42 int codec_second_size;
43 int current_codec_second_size;
45 struct AVTEA *tea_ctx;
47 int64_t current_chapter_size;
50 static int get_second_size(char *codec_name)
54 if (!strcmp(codec_name, "mp332")) {
56 } else if (!strcmp(codec_name, "acelp16")) {
58 } else if (!strcmp(codec_name, "acelp85")) {
65 static int aa_read_header(AVFormatContext *s)
67 int i, j, idx, largest_idx = -1;
68 uint32_t nkey, nval, toc_size, npairs, header_seed = 0, 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;
75 } TOC[MAX_TOC_ENTRIES];
76 uint32_t header_key_part[4];
77 uint8_t header_key[16] = {0};
78 AADemuxContext *c = s->priv_data;
79 AVIOContext *pb = s->pb;
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
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)) {
107 avio_read(pb, key, nkey); // key string
109 if (nval > sizeof(val)) {
112 avio_read(pb, val, nval); // value string
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);
118 if (!strcmp(key, "HeaderSeed")) {
119 av_log(s, AV_LOG_DEBUG, "HeaderSeed is <%s>\n", val);
120 header_seed = atoi(val);
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!
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");
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);
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);
147 /* decryption key derivation */
148 c->tea_ctx = av_tea_alloc();
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);
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);
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];
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");
171 st = avformat_new_stream(s, NULL);
173 av_freep(&c->tea_ctx);
174 return AVERROR(ENOMEM);
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;
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;
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) {
199 largest_size = current_size;
202 start = TOC[largest_idx].offset;
203 avio_seek(pb, start, SEEK_SET);
204 c->current_chapter_size = 0;
209 static int aa_read_packet(AVFormatContext *s, AVPacket *pkt)
211 uint8_t dst[TEA_BLOCK_SIZE];
212 uint8_t src[TEA_BLOCK_SIZE];
216 uint8_t buf[MAX_CODEC_SECOND_SIZE * 2];
219 AADemuxContext *c = s->priv_data;
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) {
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;
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;
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;
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;
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;
259 ret = av_new_packet(pkt, written);
262 memcpy(pkt->data, buf, written);
267 static int aa_probe(AVProbeData *p)
269 uint8_t *buf = p->buf;
271 // first 4 bytes are file size, next 4 bytes are the magic
272 if (AV_RB32(buf+4) != AA_MAGIC)
275 return AVPROBE_SCORE_MAX / 2;
278 static int aa_read_close(AVFormatContext *s)
280 AADemuxContext *c = s->priv_data;
282 av_freep(&c->tea_ctx);
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 },
296 static const AVClass aa_class = {
298 .item_name = av_default_item_name,
299 .option = aa_options,
300 .version = LIBAVUTIL_VERSION_INT,
303 AVInputFormat ff_aa_demuxer = {
305 .long_name = NULL_IF_CONFIG_SMALL("Audible AA format files"),
306 .priv_class = &aa_class,
307 .priv_data_size = sizeof(AADemuxContext),
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,