matroska.c

ffmpeg源码分析

    }

    /* read out length */
    total &= ~len_mask;
    while (n++ < read)
        total = (total << 8) | get_byte(pb);

    *number = total;

    return read;
}

/*
 * Read: the element content data ID.
 * Return: the number of bytes read or < 0 on error.
 */

static int
ebml_read_element_id (MatroskaDemuxContext *matroska,
                      uint32_t             *id,
                      int                  *level_up)
{
    int read;
    uint64_t total;

    /* if we re-call this, use our cached ID */
    if (matroska->peek_id != 0) {
        if (level_up)
            *level_up = 0;
        *id = matroska->peek_id;
        return 0;
    }

    /* read out the "EBML number", include tag in ID */
    if ((read = ebml_read_num(matroska, 4, &total)) < 0)
        return read;
    *id = matroska->peek_id  = total | (1 << (read * 7));

    /* level tracking */
    if (level_up)
        *level_up = ebml_read_element_level_up(matroska);

    return read;
}

/*
 * Read: element content length.
 * Return: the number of bytes read or < 0 on error.
 */

static int
ebml_read_element_length (MatroskaDemuxContext *matroska,
                          uint64_t             *length)
{
    /* clear cache since we're now beyond that data point */
    matroska->peek_id = 0;

    /* read out the "EBML number", include tag in ID */
    return ebml_read_num(matroska, 8, length);
}

/*
 * Return: the ID of the next element, or 0 on error.
 * Level_up contains the amount of levels that this
 * next element lies higher than the previous one.
 */

static uint32_t
ebml_peek_id (MatroskaDemuxContext *matroska,
              int                  *level_up)
{
    uint32_t id;

    assert(level_up != NULL);

    if (ebml_read_element_id(matroska, &id, level_up) < 0)
        return 0;

    return id;
}

/*
 * Seek to a given offset.
 * 0 is success, -1 is failure.
 */

static int
ebml_read_seek (MatroskaDemuxContext *matroska,
                offset_t              offset)
{
    ByteIOContext *pb = &matroska->ctx->pb;

    /* clear ID cache, if any */
    matroska->peek_id = 0;

    return (url_fseek(pb, offset, SEEK_SET) == offset) ? 0 : -1;
}

/*
 * Skip the next element.
 * 0 is success, -1 is failure.
 */

static int
ebml_read_skip (MatroskaDemuxContext *matroska)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    uint32_t id;
    uint64_t length;
    int res;

    if ((res = ebml_read_element_id(matroska, &id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &length)) < 0)
        return res;

    url_fskip(pb, length);

    return 0;
}

/*
 * Read the next element as an unsigned int.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_uint (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                uint64_t             *num)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    int n = 0, size, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;
    if (size < 1 || size > 8) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid uint element size %d at position %"PRId64" (0x%"PRIx64")\n",
                size, pos, pos);
        return AVERROR_INVALIDDATA;
    }

    /* big-endian ordening; build up number */
    *num = 0;
    while (n++ < size)
        *num = (*num << 8) | get_byte(pb);

    return 0;
}

/*
 * Read the next element as a signed int.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_sint (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                int64_t              *num)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    int size, n = 1, negative = 0, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;
    if (size < 1 || size > 8) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid sint element size %d at position %"PRId64" (0x%"PRIx64")\n",
                size, pos, pos);
        return AVERROR_INVALIDDATA;
    }
    if ((*num = get_byte(pb)) & 0x80) {
        negative = 1;
        *num &= ~0x80;
    }
    *num = 0;
    while (n++ < size)
        *num = (*num << 8) | get_byte(pb);

    /* make signed */
    if (negative)
        *num = *num - (1LL << ((8 * size) - 1));

    return 0;
}

/*
 * Read the next element as a float.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_float (MatroskaDemuxContext *matroska,
                 uint32_t             *id,
                 double               *num)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    int size, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;

    if (size == 4) {
        *num= av_int2flt(get_be32(pb));
    } else if(size==8){
        *num= av_int2dbl(get_be64(pb));
    } else if(size==10){
        av_log(matroska->ctx, AV_LOG_ERROR,
               "FIXME! 10-byte floats unimplemented\n");
        return AVERROR_UNKNOWN;
    } else{
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid float element size %d at position %"PRIu64" (0x%"PRIx64")\n",
               size, pos, pos);
        return AVERROR_INVALIDDATA;
    }

    return 0;
}

/*
 * Read the next element as an ASCII string.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_ascii (MatroskaDemuxContext *matroska,
                 uint32_t             *id,
                 char                **str)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    int size, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;

    /* ebml strings are usually not 0-terminated, so we allocate one
     * byte more, read the string and NULL-terminate it ourselves. */
    if (size < 0 || !(*str = av_malloc(size + 1))) {
        av_log(matroska->ctx, AV_LOG_ERROR, "Memory allocation failed\n");
        return AVERROR_NOMEM;
    }
    if (get_buffer(pb, (uint8_t *) *str, size) != size) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Read error at pos. %"PRIu64" (0x%"PRIx64")\n", pos, pos);
        return AVERROR_IO;
    }
    (*str)[size] = '\0';

    return 0;
}

/*
 * Read the next element as a UTF-8 string.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_utf8 (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                char                **str)
{
  return ebml_read_ascii(matroska, id, str);
}

/*
 * Read the next element as a date (nanoseconds since 1/1/2000).
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_date (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                int64_t              *date)
{
  return ebml_read_sint(matroska, id, date);
}

/*
 * Read the next element, but only the header. The contents
 * are supposed to be sub-elements which can be read separately.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_master (MatroskaDemuxContext *matroska,
                  uint32_t             *id)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    uint64_t length;
    MatroskaLevel *level;
    int res;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &length)) < 0)
        return res;

    /* protect... (Heaven forbids that the '>' is true) */
    if (matroska->num_levels >= EBML_MAX_DEPTH) {
        av_log(matroska->ctx, AV_LOG_ERROR,
               "File moves beyond max. allowed depth (%d)\n", EBML_MAX_DEPTH);
        return AVERROR_NOTSUPP;
    }

    /* remember level */
    level = &matroska->levels[matroska->num_levels++];
    level->start = url_ftell(pb);
    level->length = length;

    return 0;
}

/*
 * Read the next element as binary data.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_binary (MatroskaDemuxContext *matroska,
                  uint32_t             *id,
                  uint8_t             **binary,
                  int                  *size)
{
    ByteIOContext *pb = &matroska->ctx->pb;
    uint64_t rlength;
    int res;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    *size = rlength;

    if (!(*binary = av_malloc(*size))) {
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Memory allocation error\n");
        return AVERROR_NOMEM;
    }

    if (get_buffer(pb, *binary, *size) != *size) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Read error at pos. %"PRIu64" (0x%"PRIx64")\n", pos, pos);
        return AVERROR_IO;
    }

    return 0;
}

/*
 * Read signed/unsigned "EBML" numbers.
 * Return: number of bytes processed, < 0 on error.
 * XXX: use ebml_read_num().
 */

static int
matroska_ebmlnum_uint (uint8_t  *data,
                       uint32_t  size,
                       uint64_t *num)
{
    int len_mask = 0x80, read = 1, n = 1, num_ffs = 0;
    uint64_t total;

    if (size <= 0)
        return AVERROR_INVALIDDATA;

    total = data[0];
    while (read <= 8 && !(total & len_mask)) {
        read++;
        len_mask >>= 1;
    }
    if (read > 8)
        return AVERROR_INVALIDDATA;

    if ((total &= (len_mask - 1)) == len_mask - 1)
        num_ffs++;
    if (size < read)
        return AVERROR_INVALIDDATA;
    while (n < read) {
        if (data[n] == 0xff)
            num_ffs++;
        total = (total << 8) | data[n];
        n++;
    }

    if (read == num_ffs)
        *num = (uint64_t)-1;
    else
        *num = total;

    return read;
}

/*
 * Same as above, but signed.
 */