[FFmpeg-devel] [PATCH v3] Add support for Audible AA files

[Michael Niedermayer]

On Tue, Jul 28, 2015 at 05:25:21PM +0300, Vesselin Bontchev wrote:
> Hi,
> 
> I am attaching a new revision (v3) of the "Audible AA" patch.
> 
> Vesselin

[...]

> +    avio_skip(pb, 24); // header termination block (ignored)
> +    npairs = avio_rb32(pb); // read dictionary entries
> +    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")) {
> +            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++) {
> +                header_key.part[idx] = AV_RB32(&header_key.part[idx]); // convert to BE!
> +            }
> +        }
> +    }

there should be some check to break out of the array when the end
is reached or some error
otherwise this could take a long time with craftet data


[...]
> +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 = 0;
> +    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) {
> +            ret = AVERROR_EOF;
> +            goto end;
> +        }
> +        av_log(s, AV_LOG_DEBUG, "[aa] chapter %d (%ld 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;
> +

> +    av_new_packet(pkt, written);

missing failure check


> +    memcpy(pkt->data, buf, written);
> +

> +end:
> +    return ret;

if you dont plan to add additional stuff here then goto end could be
replaced by direct returns

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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