libavformat/aadec.c - manifest_repos/ffmpeg - Git at Google

 /*
  * Audible AA demuxer
  * Copyright (c) 2015 Vesselin Bontchev
  *
  * Header parsing is borrowed from https://github.com/jteeuwen/audible project.
  * Copyright (c) 2001-2014, Jim Teeuwen
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *
  * 1. Redistributions of source code must retain the above copyright notice, this
  *    list of conditions and the following disclaimer.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
  * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "avformat.h"
 #include "internal.h"
 #include "libavutil/dict.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/tea.h"
 #include "libavutil/opt.h"

 #define AA_MAGIC 1469084982 /* this identifies an audible .aa file */
 #define MAX_CODEC_SECOND_SIZE 3982
 #define MAX_TOC_ENTRIES 16
 #define MAX_DICTIONARY_ENTRIES 128
 #define TEA_BLOCK_SIZE 8
 #define CHAPTER_HEADER_SIZE 8
 #define TIMEPREC 1000
 #define MP3_FRAME_SIZE 104

 typedef struct AADemuxContext {
     AVClass *class;
     uint8_t *aa_fixed_key;
     int aa_fixed_key_len;
     int codec_second_size;
     int current_codec_second_size;
     int chapter_idx;
     struct AVTEA *tea_ctx;
     uint8_t file_key[16];
     int64_t current_chapter_size;
     int64_t content_start;
     int64_t content_end;
     int seek_offset;
 } AADemuxContext;

 static int get_second_size(char *codec_name)
 {
     int result = -1;

     if (!strcmp(codec_name, "mp332")) {
         result = 3982;
     } else if (!strcmp(codec_name, "acelp16")) {
         result = 2000;
     } else if (!strcmp(codec_name, "acelp85")) {
         result = 1045;
     }

     return result;
 }

 static int aa_read_header(AVFormatContext *s)
 {
     int i, j, idx, largest_idx = -1;
     uint32_t nkey, nval, toc_size, npairs, header_seed = 0, start;
     char key[128], val[128], codec_name[64] = {0};
     uint8_t output[24], dst[8], src[8];
     int64_t largest_size = -1, current_size = -1, chapter_pos;
     struct toc_entry {
         uint32_t offset;
         uint32_t size;
     } TOC[MAX_TOC_ENTRIES];
     uint32_t header_key_part[4];
     uint8_t header_key[16] = {0};
     AADemuxContext *c = s->priv_data;
     AVIOContext *pb = s->pb;
     AVStream *st;
     int ret;

     /* parse .aa header */
     avio_skip(pb, 4); // file size
     avio_skip(pb, 4); // magic string
     toc_size = avio_rb32(pb); // TOC size
     avio_skip(pb, 4); // unidentified integer
     if (toc_size > MAX_TOC_ENTRIES || toc_size < 2)
         return AVERROR_INVALIDDATA;
     for (i = 0; i < toc_size; i++) { // read TOC
         avio_skip(pb, 4); // TOC entry index
         TOC[i].offset = avio_rb32(pb); // block offset
         TOC[i].size = avio_rb32(pb); // block size
     }
     avio_skip(pb, 24); // header termination block (ignored)
     npairs = avio_rb32(pb); // read dictionary entries
     if (npairs > MAX_DICTIONARY_ENTRIES)
         return AVERROR_INVALIDDATA;
     for (i = 0; i < npairs; i++) {
         memset(val, 0, sizeof(val));
         memset(key, 0, sizeof(key));
         avio_skip(pb, 1); // unidentified integer
         nkey = avio_rb32(pb); // key string length
         nval = avio_rb32(pb); // value string length
         avio_get_str(pb, nkey, key, sizeof(key));
         avio_get_str(pb, nval, val, sizeof(val));
         if (!strcmp(key, "codec")) {
             av_log(s, AV_LOG_DEBUG, "Codec is <%s>\n", val);
             strncpy(codec_name, val, sizeof(codec_name) - 1);
         } else if (!strcmp(key, "HeaderSeed")) {
             av_log(s, AV_LOG_DEBUG, "HeaderSeed is <%s>\n", val);
             header_seed = atoi(val);
         } else if (!strcmp(key, "HeaderKey")) { // this looks like "1234567890 1234567890 1234567890 1234567890"
             av_log(s, AV_LOG_DEBUG, "HeaderKey is <%s>\n", val);

             ret = sscanf(val, "%"SCNu32"%"SCNu32"%"SCNu32"%"SCNu32,
                    &header_key_part[0], &header_key_part[1], &header_key_part[2], &header_key_part[3]);
             if (ret != 4)
                 return AVERROR_INVALIDDATA;

             for (idx = 0; idx < 4; idx++) {
                 AV_WB32(&header_key[idx * 4], header_key_part[idx]); // convert each part to BE!
             }
             av_log(s, AV_LOG_DEBUG, "Processed HeaderKey is ");
             for (i = 0; i < 16; i++)
                 av_log(s, AV_LOG_DEBUG, "%02x", header_key[i]);
             av_log(s, AV_LOG_DEBUG, "\n");
         } else {
             av_dict_set(&s->metadata, key, val, 0);
         }
     }

     /* verify fixed key */
     if (c->aa_fixed_key_len != 16) {
         av_log(s, AV_LOG_ERROR, "aa_fixed_key value needs to be 16 bytes!\n");
         return AVERROR(EINVAL);
     }

     /* verify codec */
     if ((c->codec_second_size = get_second_size(codec_name)) == -1) {
         av_log(s, AV_LOG_ERROR, "unknown codec <%s>!\n", codec_name);
         return AVERROR(EINVAL);
     }

     /* decryption key derivation */
     c->tea_ctx = av_tea_alloc();
     if (!c->tea_ctx)
         return AVERROR(ENOMEM);
     av_tea_init(c->tea_ctx, c->aa_fixed_key, 16);
     output[0] = output[1] = 0; // purely for padding purposes
     memcpy(output + 2, header_key, 16);
     idx = 0;
     for (i = 0; i < 3; i++) { // TEA CBC with weird mixed endianness
         AV_WB32(src, header_seed);
         AV_WB32(src + 4, header_seed + 1);
         header_seed += 2;
         av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 0); // TEA ECB encrypt
         for (j = 0; j < TEA_BLOCK_SIZE && idx < 18; j+=1, idx+=1) {
             output[idx] = output[idx] ^ dst[j];
         }
     }
     memcpy(c->file_key, output + 2, 16); // skip first 2 bytes of output
     av_log(s, AV_LOG_DEBUG, "File key is ");
     for (i = 0; i < 16; i++)
         av_log(s, AV_LOG_DEBUG, "%02x", c->file_key[i]);
     av_log(s, AV_LOG_DEBUG, "\n");

     /* decoder setup */
     st = avformat_new_stream(s, NULL);
     if (!st) {
         av_freep(&c->tea_ctx);
         return AVERROR(ENOMEM);
     }
     st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
     if (!strcmp(codec_name, "mp332")) {
         st->codecpar->codec_id = AV_CODEC_ID_MP3;
         st->codecpar->sample_rate = 22050;
         st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
         avpriv_set_pts_info(st, 64, 8, 32000 * TIMEPREC);
         // encoded audio frame is MP3_FRAME_SIZE bytes (+1 with padding, unlikely)
     } else if (!strcmp(codec_name, "acelp85")) {
         st->codecpar->codec_id = AV_CODEC_ID_SIPR;
         st->codecpar->block_align = 19;
         st->codecpar->channels = 1;
         st->codecpar->sample_rate = 8500;
         st->codecpar->bit_rate = 8500;
         st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
         avpriv_set_pts_info(st, 64, 8, 8500 * TIMEPREC);
     } else if (!strcmp(codec_name, "acelp16")) {
         st->codecpar->codec_id = AV_CODEC_ID_SIPR;
         st->codecpar->block_align = 20;
         st->codecpar->channels = 1;
         st->codecpar->sample_rate = 16000;
         st->codecpar->bit_rate = 16000;
         st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
         avpriv_set_pts_info(st, 64, 8, 16000 * TIMEPREC);
     }

     /* determine, and jump to audio start offset */
     for (i = 1; i < toc_size; i++) { // skip the first entry!
         current_size = TOC[i].size;
         if (current_size > largest_size) {
             largest_idx = i;
             largest_size = current_size;
         }
     }
     start = TOC[largest_idx].offset;
     avio_seek(pb, start, SEEK_SET);

     // extract chapter positions. since all formats have constant bit rate, use it
     // as time base in bytes/s, for easy stream position <-> timestamp conversion
     st->start_time = 0;
     c->content_start = start;
     c->content_end = start + largest_size;

     while ((chapter_pos = avio_tell(pb)) >= 0 && chapter_pos < c->content_end) {
         int chapter_idx = s->nb_chapters;
         uint32_t chapter_size = avio_rb32(pb);
         if (chapter_size == 0) break;
         chapter_pos -= start + CHAPTER_HEADER_SIZE * chapter_idx;
         avio_skip(pb, 4 + chapter_size);
         if (!avpriv_new_chapter(s, chapter_idx, st->time_base,
             chapter_pos * TIMEPREC, (chapter_pos + chapter_size) * TIMEPREC, NULL))
                 return AVERROR(ENOMEM);
     }

     st->duration = (largest_size - CHAPTER_HEADER_SIZE * s->nb_chapters) * TIMEPREC;

     ff_update_cur_dts(s, st, 0);
     avio_seek(pb, start, SEEK_SET);
     c->current_chapter_size = 0;
     c->seek_offset = 0;

     return 0;
 }

 static int aa_read_packet(AVFormatContext *s, AVPacket *pkt)
 {
     uint8_t dst[TEA_BLOCK_SIZE];
     uint8_t src[TEA_BLOCK_SIZE];
     int i;
     int trailing_bytes;
     int blocks;
     uint8_t buf[MAX_CODEC_SECOND_SIZE * 2];
     int written = 0;
     int ret;
     AADemuxContext *c = s->priv_data;
     uint64_t pos = avio_tell(s->pb);

     // are we at the end of the audio content?
     if (pos >= c->content_end) {
         return AVERROR_EOF;
     }

     // are we at the start of a chapter?
     if (c->current_chapter_size == 0) {
         c->current_chapter_size = avio_rb32(s->pb);
         if (c->current_chapter_size == 0) {
             return AVERROR_EOF;
         }
         av_log(s, AV_LOG_DEBUG, "Chapter %d (%" PRId64 " bytes)\n", c->chapter_idx, c->current_chapter_size);
         c->chapter_idx = c->chapter_idx + 1;
         avio_skip(s->pb, 4); // data start offset
         pos += 8;
         c->current_codec_second_size = c->codec_second_size;
     }

     // is this the last block in this chapter?
     if (c->current_chapter_size / c->current_codec_second_size == 0) {
         c->current_codec_second_size = c->current_chapter_size % c->current_codec_second_size;
     }

     // decrypt c->current_codec_second_size bytes
     blocks = c->current_codec_second_size / TEA_BLOCK_SIZE;
     for (i = 0; i < blocks; i++) {
         ret = avio_read(s->pb, src, TEA_BLOCK_SIZE);
         if (ret != TEA_BLOCK_SIZE)
             return (ret < 0) ? ret : AVERROR_EOF;
         av_tea_init(c->tea_ctx, c->file_key, 16);
         av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 1);
         memcpy(buf + written, dst, TEA_BLOCK_SIZE);
         written = written + TEA_BLOCK_SIZE;
     }
     trailing_bytes = c->current_codec_second_size % TEA_BLOCK_SIZE;
     if (trailing_bytes != 0) { // trailing bytes are left unencrypted!
         ret = avio_read(s->pb, src, trailing_bytes);
         if (ret != trailing_bytes)
             return (ret < 0) ? ret : AVERROR_EOF;
         memcpy(buf + written, src, trailing_bytes);
         written = written + trailing_bytes;
     }

     // update state
     c->current_chapter_size = c->current_chapter_size - c->current_codec_second_size;
     if (c->current_chapter_size <= 0)
         c->current_chapter_size = 0;

     if (c->seek_offset > written)
         c->seek_offset = 0; // ignore wrong estimate

     ret = av_new_packet(pkt, written - c->seek_offset);
     if (ret < 0)
         return ret;
     memcpy(pkt->data, buf + c->seek_offset, written - c->seek_offset);
     pkt->pos = pos;

     c->seek_offset = 0;
     return 0;
 }

 static int aa_read_seek(AVFormatContext *s,
                         int stream_index, int64_t timestamp, int flags)
 {
     AADemuxContext *c = s->priv_data;
     AVChapter *ch;
     int64_t chapter_pos, chapter_start, chapter_size;
     int chapter_idx = 0;

     // find chapter containing seek timestamp
     if (timestamp < 0)
         timestamp = 0;

     while (chapter_idx < s->nb_chapters && timestamp >= s->chapters[chapter_idx]->end) {
         ++chapter_idx;
     }

     if (chapter_idx >= s->nb_chapters) {
         chapter_idx = s->nb_chapters - 1;
         if (chapter_idx < 0) return -1; // there is no chapter.
         timestamp = s->chapters[chapter_idx]->end;
     }

     ch = s->chapters[chapter_idx];

     // sync by clamping timestamp to nearest valid block position in its chapter
     chapter_size = ch->end / TIMEPREC - ch->start / TIMEPREC;
     chapter_pos = av_rescale_rnd((timestamp - ch->start) / TIMEPREC,
         1, c->codec_second_size,
         (flags & AVSEEK_FLAG_BACKWARD) ? AV_ROUND_DOWN : AV_ROUND_UP)
         * c->codec_second_size;
     if (chapter_pos >= chapter_size)
         chapter_pos = chapter_size;
     chapter_start = c->content_start + (ch->start / TIMEPREC) + CHAPTER_HEADER_SIZE * (1 + chapter_idx);

     // reinit read state
     avio_seek(s->pb, chapter_start + chapter_pos, SEEK_SET);
     c->current_codec_second_size = c->codec_second_size;
     c->current_chapter_size = chapter_size - chapter_pos;
     c->chapter_idx = 1 + chapter_idx;

     // for unaligned frames, estimate offset of first frame in block (assume no padding)
     if (s->streams[0]->codecpar->codec_id == AV_CODEC_ID_MP3) {
         c->seek_offset = (MP3_FRAME_SIZE - chapter_pos % MP3_FRAME_SIZE) % MP3_FRAME_SIZE;
     }

     ff_update_cur_dts(s, s->streams[0], ch->start + (chapter_pos + c->seek_offset) * TIMEPREC);

     return 1;
 }

 static int aa_probe(const AVProbeData *p)
 {
     uint8_t *buf = p->buf;

     // first 4 bytes are file size, next 4 bytes are the magic
     if (AV_RB32(buf+4) != AA_MAGIC)
         return 0;

     return AVPROBE_SCORE_MAX / 2;
 }

 static int aa_read_close(AVFormatContext *s)
 {
     AADemuxContext *c = s->priv_data;

     av_freep(&c->tea_ctx);

     return 0;
 }

 #define OFFSET(x) offsetof(AADemuxContext, x)
 static const AVOption aa_options[] = {
     { "aa_fixed_key", // extracted from libAAX_SDK.so and AAXSDKWin.dll files!
         "Fixed key used for handling Audible AA files", OFFSET(aa_fixed_key),
         AV_OPT_TYPE_BINARY, {.str="77214d4b196a87cd520045fd2a51d673"},
         .flags = AV_OPT_FLAG_DECODING_PARAM },
     { NULL },
 };

 static const AVClass aa_class = {
     .class_name = "aa",
     .item_name  = av_default_item_name,
     .option     = aa_options,
     .version    = LIBAVUTIL_VERSION_INT,
 };

 AVInputFormat ff_aa_demuxer = {
     .name           = "aa",
     .long_name      = NULL_IF_CONFIG_SMALL("Audible AA format files"),
     .priv_class     = &aa_class,
     .priv_data_size = sizeof(AADemuxContext),
     .extensions     = "aa",
     .read_probe     = aa_probe,
     .read_header    = aa_read_header,
     .read_packet    = aa_read_packet,
     .read_seek      = aa_read_seek,
     .read_close     = aa_read_close,
     .flags          = AVFMT_NO_BYTE_SEEK | AVFMT_NOGENSEARCH,
 };
	/*
	* Audible AA demuxer
	* Copyright (c) 2015 Vesselin Bontchev
	*
	* Header parsing is borrowed from https://github.com/jteeuwen/audible project.
	* Copyright (c) 2001-2014, Jim Teeuwen
	*
	* Redistribution and use in source and binary forms, with or without modification,
	* are permitted provided that the following conditions are met:
	*
	* 1. Redistributions of source code must retain the above copyright notice, this
	* list of conditions and the following disclaimer.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
	* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
	* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
	* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
	* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
	* ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
	* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "avformat.h"
	#include "internal.h"
	#include "libavutil/dict.h"
	#include "libavutil/intreadwrite.h"
	#include "libavutil/tea.h"
	#include "libavutil/opt.h"

	#define AA_MAGIC 1469084982 /* this identifies an audible .aa file */
	#define MAX_CODEC_SECOND_SIZE 3982
	#define MAX_TOC_ENTRIES 16
	#define MAX_DICTIONARY_ENTRIES 128
	#define TEA_BLOCK_SIZE 8
	#define CHAPTER_HEADER_SIZE 8
	#define TIMEPREC 1000
	#define MP3_FRAME_SIZE 104

	typedef struct AADemuxContext {
	AVClass *class;
	uint8_t *aa_fixed_key;
	int aa_fixed_key_len;
	int codec_second_size;
	int current_codec_second_size;
	int chapter_idx;
	struct AVTEA *tea_ctx;
	uint8_t file_key[16];
	int64_t current_chapter_size;
	int64_t content_start;
	int64_t content_end;
	int seek_offset;
	} AADemuxContext;

	static int get_second_size(char *codec_name)
	{
	int result = -1;

	if (!strcmp(codec_name, "mp332")) {
	result = 3982;
	} else if (!strcmp(codec_name, "acelp16")) {
	result = 2000;
	} else if (!strcmp(codec_name, "acelp85")) {
	result = 1045;
	}

	return result;
	}

	static int aa_read_header(AVFormatContext *s)
	{
	int i, j, idx, largest_idx = -1;
	uint32_t nkey, nval, toc_size, npairs, header_seed = 0, start;
	char key[128], val[128], codec_name[64] = {0};
	uint8_t output[24], dst[8], src[8];
	int64_t largest_size = -1, current_size = -1, chapter_pos;
	struct toc_entry {
	uint32_t offset;
	uint32_t size;
	} TOC[MAX_TOC_ENTRIES];
	uint32_t header_key_part[4];
	uint8_t header_key[16] = {0};
	AADemuxContext *c = s->priv_data;
	AVIOContext *pb = s->pb;
	AVStream *st;
	int ret;

	/* parse .aa header */
	avio_skip(pb, 4); // file size
	avio_skip(pb, 4); // magic string
	toc_size = avio_rb32(pb); // TOC size
	avio_skip(pb, 4); // unidentified integer
	if (toc_size > MAX_TOC_ENTRIES \|\| toc_size < 2)
	return AVERROR_INVALIDDATA;
	for (i = 0; i < toc_size; i++) { // read TOC
	avio_skip(pb, 4); // TOC entry index
	TOC[i].offset = avio_rb32(pb); // block offset
	TOC[i].size = avio_rb32(pb); // block size
	}
	avio_skip(pb, 24); // header termination block (ignored)
	npairs = avio_rb32(pb); // read dictionary entries
	if (npairs > MAX_DICTIONARY_ENTRIES)
	return AVERROR_INVALIDDATA;
	for (i = 0; i < npairs; i++) {
	memset(val, 0, sizeof(val));
	memset(key, 0, sizeof(key));
	avio_skip(pb, 1); // unidentified integer
	nkey = avio_rb32(pb); // key string length
	nval = avio_rb32(pb); // value string length
	avio_get_str(pb, nkey, key, sizeof(key));
	avio_get_str(pb, nval, val, sizeof(val));
	if (!strcmp(key, "codec")) {
	av_log(s, AV_LOG_DEBUG, "Codec is <%s>\n", val);
	strncpy(codec_name, val, sizeof(codec_name) - 1);
	} else if (!strcmp(key, "HeaderSeed")) {
	av_log(s, AV_LOG_DEBUG, "HeaderSeed is <%s>\n", val);
	header_seed = atoi(val);
	} else if (!strcmp(key, "HeaderKey")) { // this looks like "1234567890 1234567890 1234567890 1234567890"
	av_log(s, AV_LOG_DEBUG, "HeaderKey is <%s>\n", val);

	ret = sscanf(val, "%"SCNu32"%"SCNu32"%"SCNu32"%"SCNu32,
	&header_key_part[0], &header_key_part[1], &header_key_part[2], &header_key_part[3]);
	if (ret != 4)
	return AVERROR_INVALIDDATA;

	for (idx = 0; idx < 4; idx++) {
	AV_WB32(&header_key[idx * 4], header_key_part[idx]); // convert each part to BE!
	}
	av_log(s, AV_LOG_DEBUG, "Processed HeaderKey is ");
	for (i = 0; i < 16; i++)
	av_log(s, AV_LOG_DEBUG, "%02x", header_key[i]);
	av_log(s, AV_LOG_DEBUG, "\n");
	} else {
	av_dict_set(&s->metadata, key, val, 0);
	}
	}

	/* verify fixed key */
	if (c->aa_fixed_key_len != 16) {
	av_log(s, AV_LOG_ERROR, "aa_fixed_key value needs to be 16 bytes!\n");
	return AVERROR(EINVAL);
	}

	/* verify codec */
	if ((c->codec_second_size = get_second_size(codec_name)) == -1) {
	av_log(s, AV_LOG_ERROR, "unknown codec <%s>!\n", codec_name);
	return AVERROR(EINVAL);
	}

	/* decryption key derivation */
	c->tea_ctx = av_tea_alloc();
	if (!c->tea_ctx)
	return AVERROR(ENOMEM);
	av_tea_init(c->tea_ctx, c->aa_fixed_key, 16);
	output[0] = output[1] = 0; // purely for padding purposes
	memcpy(output + 2, header_key, 16);
	idx = 0;
	for (i = 0; i < 3; i++) { // TEA CBC with weird mixed endianness
	AV_WB32(src, header_seed);
	AV_WB32(src + 4, header_seed + 1);
	header_seed += 2;
	av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 0); // TEA ECB encrypt
	for (j = 0; j < TEA_BLOCK_SIZE && idx < 18; j+=1, idx+=1) {
	output[idx] = output[idx] ^ dst[j];
	}
	}
	memcpy(c->file_key, output + 2, 16); // skip first 2 bytes of output
	av_log(s, AV_LOG_DEBUG, "File key is ");
	for (i = 0; i < 16; i++)
	av_log(s, AV_LOG_DEBUG, "%02x", c->file_key[i]);
	av_log(s, AV_LOG_DEBUG, "\n");

	/* decoder setup */
	st = avformat_new_stream(s, NULL);
	if (!st) {
	av_freep(&c->tea_ctx);
	return AVERROR(ENOMEM);
	}
	st->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
	if (!strcmp(codec_name, "mp332")) {
	st->codecpar->codec_id = AV_CODEC_ID_MP3;
	st->codecpar->sample_rate = 22050;
	st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
	avpriv_set_pts_info(st, 64, 8, 32000 * TIMEPREC);
	// encoded audio frame is MP3_FRAME_SIZE bytes (+1 with padding, unlikely)
	} else if (!strcmp(codec_name, "acelp85")) {
	st->codecpar->codec_id = AV_CODEC_ID_SIPR;
	st->codecpar->block_align = 19;
	st->codecpar->channels = 1;
	st->codecpar->sample_rate = 8500;
	st->codecpar->bit_rate = 8500;
	st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
	avpriv_set_pts_info(st, 64, 8, 8500 * TIMEPREC);
	} else if (!strcmp(codec_name, "acelp16")) {
	st->codecpar->codec_id = AV_CODEC_ID_SIPR;
	st->codecpar->block_align = 20;
	st->codecpar->channels = 1;
	st->codecpar->sample_rate = 16000;
	st->codecpar->bit_rate = 16000;
	st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
	avpriv_set_pts_info(st, 64, 8, 16000 * TIMEPREC);
	}

	/* determine, and jump to audio start offset */
	for (i = 1; i < toc_size; i++) { // skip the first entry!
	current_size = TOC[i].size;
	if (current_size > largest_size) {
	largest_idx = i;
	largest_size = current_size;
	}
	}
	start = TOC[largest_idx].offset;
	avio_seek(pb, start, SEEK_SET);

	// extract chapter positions. since all formats have constant bit rate, use it
	// as time base in bytes/s, for easy stream position <-> timestamp conversion
	st->start_time = 0;
	c->content_start = start;
	c->content_end = start + largest_size;

	while ((chapter_pos = avio_tell(pb)) >= 0 && chapter_pos < c->content_end) {
	int chapter_idx = s->nb_chapters;
	uint32_t chapter_size = avio_rb32(pb);
	if (chapter_size == 0) break;
	chapter_pos -= start + CHAPTER_HEADER_SIZE * chapter_idx;
	avio_skip(pb, 4 + chapter_size);
	if (!avpriv_new_chapter(s, chapter_idx, st->time_base,
	chapter_pos * TIMEPREC, (chapter_pos + chapter_size) * TIMEPREC, NULL))
	return AVERROR(ENOMEM);
	}

	st->duration = (largest_size - CHAPTER_HEADER_SIZE * s->nb_chapters) * TIMEPREC;

	ff_update_cur_dts(s, st, 0);
	avio_seek(pb, start, SEEK_SET);
	c->current_chapter_size = 0;
	c->seek_offset = 0;

	return 0;
	}

	static int aa_read_packet(AVFormatContext s, AVPacket pkt)
	{
	uint8_t dst[TEA_BLOCK_SIZE];
	uint8_t src[TEA_BLOCK_SIZE];
	int i;
	int trailing_bytes;
	int blocks;
	uint8_t buf[MAX_CODEC_SECOND_SIZE * 2];
	int written = 0;
	int ret;
	AADemuxContext *c = s->priv_data;
	uint64_t pos = avio_tell(s->pb);

	// are we at the end of the audio content?
	if (pos >= c->content_end) {
	return AVERROR_EOF;
	}

	// are we at the start of a chapter?
	if (c->current_chapter_size == 0) {
	c->current_chapter_size = avio_rb32(s->pb);
	if (c->current_chapter_size == 0) {
	return AVERROR_EOF;
	}
	av_log(s, AV_LOG_DEBUG, "Chapter %d (%" PRId64 " bytes)\n", c->chapter_idx, c->current_chapter_size);
	c->chapter_idx = c->chapter_idx + 1;
	avio_skip(s->pb, 4); // data start offset
	pos += 8;
	c->current_codec_second_size = c->codec_second_size;
	}

	// is this the last block in this chapter?
	if (c->current_chapter_size / c->current_codec_second_size == 0) {
	c->current_codec_second_size = c->current_chapter_size % c->current_codec_second_size;
	}

	// decrypt c->current_codec_second_size bytes
	blocks = c->current_codec_second_size / TEA_BLOCK_SIZE;
	for (i = 0; i < blocks; i++) {
	ret = avio_read(s->pb, src, TEA_BLOCK_SIZE);
	if (ret != TEA_BLOCK_SIZE)
	return (ret < 0) ? ret : AVERROR_EOF;
	av_tea_init(c->tea_ctx, c->file_key, 16);
	av_tea_crypt(c->tea_ctx, dst, src, 1, NULL, 1);
	memcpy(buf + written, dst, TEA_BLOCK_SIZE);
	written = written + TEA_BLOCK_SIZE;
	}
	trailing_bytes = c->current_codec_second_size % TEA_BLOCK_SIZE;
	if (trailing_bytes != 0) { // trailing bytes are left unencrypted!
	ret = avio_read(s->pb, src, trailing_bytes);
	if (ret != trailing_bytes)
	return (ret < 0) ? ret : AVERROR_EOF;
	memcpy(buf + written, src, trailing_bytes);
	written = written + trailing_bytes;
	}

	// update state
	c->current_chapter_size = c->current_chapter_size - c->current_codec_second_size;
	if (c->current_chapter_size <= 0)
	c->current_chapter_size = 0;

	if (c->seek_offset > written)
	c->seek_offset = 0; // ignore wrong estimate

	ret = av_new_packet(pkt, written - c->seek_offset);
	if (ret < 0)
	return ret;
	memcpy(pkt->data, buf + c->seek_offset, written - c->seek_offset);
	pkt->pos = pos;

	c->seek_offset = 0;
	return 0;
	}

	static int aa_read_seek(AVFormatContext *s,
	int stream_index, int64_t timestamp, int flags)
	{
	AADemuxContext *c = s->priv_data;
	AVChapter *ch;
	int64_t chapter_pos, chapter_start, chapter_size;
	int chapter_idx = 0;

	// find chapter containing seek timestamp
	if (timestamp < 0)
	timestamp = 0;

	while (chapter_idx < s->nb_chapters && timestamp >= s->chapters[chapter_idx]->end) {
	++chapter_idx;
	}

	if (chapter_idx >= s->nb_chapters) {
	chapter_idx = s->nb_chapters - 1;
	if (chapter_idx < 0) return -1; // there is no chapter.
	timestamp = s->chapters[chapter_idx]->end;
	}

	ch = s->chapters[chapter_idx];

	// sync by clamping timestamp to nearest valid block position in its chapter
	chapter_size = ch->end / TIMEPREC - ch->start / TIMEPREC;
	chapter_pos = av_rescale_rnd((timestamp - ch->start) / TIMEPREC,
	1, c->codec_second_size,
	(flags & AVSEEK_FLAG_BACKWARD) ? AV_ROUND_DOWN : AV_ROUND_UP)
	* c->codec_second_size;
	if (chapter_pos >= chapter_size)
	chapter_pos = chapter_size;
	chapter_start = c->content_start + (ch->start / TIMEPREC) + CHAPTER_HEADER_SIZE * (1 + chapter_idx);

	// reinit read state
	avio_seek(s->pb, chapter_start + chapter_pos, SEEK_SET);
	c->current_codec_second_size = c->codec_second_size;
	c->current_chapter_size = chapter_size - chapter_pos;
	c->chapter_idx = 1 + chapter_idx;

	// for unaligned frames, estimate offset of first frame in block (assume no padding)
	if (s->streams[0]->codecpar->codec_id == AV_CODEC_ID_MP3) {
	c->seek_offset = (MP3_FRAME_SIZE - chapter_pos % MP3_FRAME_SIZE) % MP3_FRAME_SIZE;
	}

	ff_update_cur_dts(s, s->streams[0], ch->start + (chapter_pos + c->seek_offset) * TIMEPREC);

	return 1;
	}

	static int aa_probe(const AVProbeData *p)
	{
	uint8_t *buf = p->buf;

	// first 4 bytes are file size, next 4 bytes are the magic
	if (AV_RB32(buf+4) != AA_MAGIC)
	return 0;

	return AVPROBE_SCORE_MAX / 2;
	}

	static int aa_read_close(AVFormatContext *s)
	{
	AADemuxContext *c = s->priv_data;

	av_freep(&c->tea_ctx);

	return 0;
	}

	#define OFFSET(x) offsetof(AADemuxContext, x)
	static const AVOption aa_options[] = {
	{ "aa_fixed_key", // extracted from libAAX_SDK.so and AAXSDKWin.dll files!
	"Fixed key used for handling Audible AA files", OFFSET(aa_fixed_key),
	AV_OPT_TYPE_BINARY, {.str="77214d4b196a87cd520045fd2a51d673"},
	.flags = AV_OPT_FLAG_DECODING_PARAM },
	{ NULL },
	};

	static const AVClass aa_class = {
	.class_name = "aa",
	.item_name = av_default_item_name,
	.option = aa_options,
	.version = LIBAVUTIL_VERSION_INT,
	};

	AVInputFormat ff_aa_demuxer = {
	.name = "aa",
	.long_name = NULL_IF_CONFIG_SMALL("Audible AA format files"),
	.priv_class = &aa_class,
	.priv_data_size = sizeof(AADemuxContext),
	.extensions = "aa",
	.read_probe = aa_probe,
	.read_header = aa_read_header,
	.read_packet = aa_read_packet,
	.read_seek = aa_read_seek,
	.read_close = aa_read_close,
	.flags = AVFMT_NO_BYTE_SEEK \| AVFMT_NOGENSEARCH,
	};