Add support for Audible AA files

https://en.wikipedia.org/wiki/Audible.com#Quality

MAINTAINERS

@@ -399,6 +399,7 @@ Generic parts:
 
 Muxers/Demuxers:
   4xm.c                                 Mike Melanson
+  aadec.c                               Vesselin Bontchev (vesselin.bontchev at yandex dot com)
   adtsenc.c                             Robert Swain
   afc.c                                 Paul B Mahol
   aiffdec.c                             Baptiste Coudurier, Matthieu Bouron

doc/demuxers.texi

@@ -18,6 +18,12 @@ enabled demuxers.
 
 The description of some of the currently available demuxers follows.
 
+@section aa
+
+Audible Format 2, 3, and 4 demuxer.
+
+This demuxer is used to demux Audible Format 2, 3, and 4 (.aa) files.
+
 @section applehttp
 
 Apple HTTP Live Streaming demuxer.

doc/general.texi

@@ -228,6 +228,8 @@ library:
 @item 8088flex TMV              @tab   @tab X
 @item AAX                       @tab   @tab X
     @tab Audible Enhanced Audio format, used in audiobooks.
+@item AA                        @tab   @tab X
+    @tab Audible Format 2, 3, and 4, used in audiobooks.
 @item ACT Voice                 @tab   @tab X
     @tab contains G.729 audio
 @item Adobe Filmstrip           @tab X @tab X

libavformat/Makefile

@@ -59,6 +59,7 @@ OBJS-$(CONFIG_SHARED)                    += log2_tab.o golomb_tab.o
 
 # muxers/demuxers
 OBJS-$(CONFIG_A64_MUXER)                 += a64.o rawenc.o
+OBJS-$(CONFIG_AA_DEMUXER)                += aadec.o
 OBJS-$(CONFIG_AAC_DEMUXER)               += aacdec.o apetag.o img2.o rawdec.o
 OBJS-$(CONFIG_AC3_DEMUXER)               += ac3dec.o rawdec.o
 OBJS-$(CONFIG_AC3_MUXER)                 += rawenc.o

libavformat/aadec.c

+/*
+ * 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/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
+
+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;
+} 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, 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;
+    struct toc_entry {
+        uint32_t offset;
+        uint32_t size;
+    } TOC[MAX_TOC_ENTRIES];
+    uint32_t header_key_part[4];
+    uint8_t header_key[16];
+    AADemuxContext *c = s->priv_data;
+    AVIOContext *pb = s->pb;
+    AVStream *st;
+
+    /* 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)
+        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
+        if (nkey > sizeof(key)) {
+            avio_skip(pb, nkey);
+        } else {
+            avio_read(pb, key, nkey); // key string
+        }
+        if (nval > sizeof(val)) {
+            avio_skip(pb, nval);
+        } else {
+            avio_read(pb, val, nval); // value string
+        }
+        if (!strcmp(key, "codec")) {
+            strncpy(codec_name, val, sizeof(codec_name) - 1);
+        }
+        if (!strcmp(key, "HeaderSeed")) {
+            header_seed = atoi(val);
+        }
+        if (!strcmp(key, "HeaderKey")) { // this looks like "1234567890 1234567890 1234567890 1234567890"
+            sscanf(val, "%d%d%d%d", &header_key_part[0], &header_key_part[1], &header_key_part[2], &header_key_part[3]);
+            for (idx = 0; idx < 4; idx++) {
+                AV_WB32(&header_key[idx * 4], header_key_part[idx]); // convert each part to BE!
+            }
+        }
+    }
+
+    /* 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
+
+    /* decoder setup */
+    st = avformat_new_stream(s, NULL);
+    if (!st) {
+        av_freep(&c->tea_ctx);
+        return AVERROR(ENOMEM);
+    }
+    st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
+    if (!strcmp(codec_name, "mp332")) {
+        st->codec->codec_id = AV_CODEC_ID_MP3;
+        st->codec->sample_rate = 22050;
+        st->need_parsing = AVSTREAM_PARSE_FULL_RAW;
+        st->start_time = 0;
+    } else if (!strcmp(codec_name, "acelp85")) {
+        st->codec->codec_id = AV_CODEC_ID_SIPR;
+        st->codec->block_align = 19;
+        st->codec->channels = 1;
+        st->codec->sample_rate = 8500;
+    } else if (!strcmp(codec_name, "acelp16")) {
+        st->codec->codec_id = AV_CODEC_ID_SIPR;
+        st->codec->block_align = 20;
+        st->codec->channels = 1;
+        st->codec->sample_rate = 16000;
+    }
+
+    /* 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);
+    c->current_chapter_size = 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;
+
+    // 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
+        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++) {
+        avio_read(s->pb, src, TEA_BLOCK_SIZE);
+        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!
+        avio_read(s->pb, src, trailing_bytes);
+        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;
+
+    ret = av_new_packet(pkt, written);
+    if (ret < 0)
+        return ret;
+    memcpy(pkt->data, buf, written);
+
+    return 0;
+}
+
+static int aa_probe(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_close     = aa_read_close,
+    .flags          = AVFMT_GENERIC_INDEX,
+};

libavformat/allformats.c

@@ -60,6 +60,7 @@ void av_register_all(void)
 
     /* (de)muxers */
     REGISTER_MUXER   (A64,              a64);
+    REGISTER_DEMUXER (AA,               aa);
     REGISTER_DEMUXER (AAC,              aac);
     REGISTER_MUXDEMUX(AC3,              ac3);
     REGISTER_DEMUXER (ACT,              act);