Function decode_tilehdr

libavcodec/wmaprodec.c:509–595

*@brief Decode how the data in the frame is split into subframes. * Every WMA frame contains the encoded data for a fixed number of * samples per channel. The data for every channel might be split * into several subframes. This function will reconstruct the list of * subframes for every channel. * * If the subframes are not evenly split, the algorithm estimates

 *@return 0 on success, < 0 in case of an error
 */
static int decode_tilehdr(WMAProDecodeCtx *s)
{
    uint16_t num_samples[WMAPRO_MAX_CHANNELS];        /** sum of samples for all currently known subframes of a channel */
    uint8_t  contains_subframe[WMAPRO_MAX_CHANNELS];  /** flag indicating if a channel contains the current subframe */
    int channels_for_cur_subframe = s->num_channels;  /** number of channels that contain the current subframe */
    int fixed_channel_layout = 0;                     /** flag indicating that all channels use the same subframe offsets and sizes */
    int min_channel_len = 0;                          /** smallest sum of samples (channels with this length will be processed first) */
    int c;

    /* Should never consume more than 3073 bits (256 iterations for the
     * while loop when always the minimum amount of 128 samples is substracted
     * from missing samples in the 8 channel case).
     * 1 + BLOCK_MAX_SIZE * MAX_CHANNELS / BLOCK_MIN_SIZE * (MAX_CHANNELS  + 4)
     */

    /** reset tiling information */
    for (c = 0; c < s->num_channels; c++)
        s->channel[c].num_subframes = 0;

    memset(num_samples, 0, sizeof(num_samples));

    if (s->max_num_subframes == 1 || get_bits1(&s->gb))
        fixed_channel_layout = 1;

    /** loop until the frame data is split between the subframes */
    do {
        int subframe_len;

        /** check which channels contain the subframe */
        for (c = 0; c < s->num_channels; c++) {
            if (num_samples[c] == min_channel_len) {
                if (fixed_channel_layout || channels_for_cur_subframe == 1 ||
                   (min_channel_len == s->samples_per_frame - s->min_samples_per_subframe))
                    contains_subframe[c] = 1;
                else
                    contains_subframe[c] = get_bits1(&s->gb);
            } else
                contains_subframe[c] = 0;
        }

        /** get subframe length, subframe_len == 0 is not allowed */
        if ((subframe_len = decode_subframe_length(s, min_channel_len)) <= 0)
            return AVERROR_INVALIDDATA;

        /** add subframes to the individual channels and find new min_channel_len */
        min_channel_len += subframe_len;
        for (c = 0; c < s->num_channels; c++) {
            WMAProChannelCtx* chan = &s->channel[c];

            if (contains_subframe[c]) {
                if (chan->num_subframes >= MAX_SUBFRAMES) {
                    av_log(s->avctx, AV_LOG_ERROR,
                           "broken frame: num subframes > 31\n");
                    return AVERROR_INVALIDDATA;
                }
                chan->subframe_len[chan->num_subframes] = subframe_len;
                num_samples[c] += subframe_len;
                ++chan->num_subframes;