PeerStreamer

 * Rewinds the ByteIOContext using the specified buffer containing the first buf_size bytes of the file.

 * Used after probing to avoid seeking.

 * Joins buf and s->buffer, taking any overlap into consideration.

 * @note s->buffer must overlap with buf or they can't be joined and the function fails

 * @note This function is NOT part of the public API

 *

 * @param s The read-only ByteIOContext to rewind

 * @param buf The probe buffer containing the first buf_size bytes of the file

 * @param buf_size The size of buf

 * @return 0 in case of success, a negative value corresponding to an

 * AVERROR code in case of failure

 */

int ff_rewind_with_probe_data(ByteIOContext *s, unsigned char *buf, int buf_size);

/**

    int max_buffer_size = s->max_packet_size ? s->max_packet_size : IO_BUFFER_SIZE;

    /* make buffer smaller in case it ended up large after probing */

    if (s->buffer_size > max_buffer_size) {

        url_setbufsize(s, max_buffer_size);

        s->checksum_ptr = dst = s->buffer;

        len = s->buffer_size;

    }

int ff_rewind_with_probe_data(ByteIOContext *s, unsigned char *buf, int buf_size)

{

    int64_t buffer_start;

    int buffer_size;

    int overlap, new_size;

    if (s->write_flag)

        return AVERROR(EINVAL);

    buffer_size = s->buf_end - s->buffer;

    /* the buffers must touch or overlap */

    if ((buffer_start = s->pos - buffer_size) > buf_size)

        return AVERROR(EINVAL);

    overlap = buf_size - buffer_start;

    new_size = buf_size + buffer_size - overlap;

    if (new_size > buf_size) {

        if (!(buf = av_realloc(buf, new_size)))

            return AVERROR(ENOMEM);

        memcpy(buf + buf_size, s->buffer + overlap, buffer_size - overlap);

        buf_size = new_size;

    }

    av_free(s->buffer);

    s->buf_ptr = s->buffer = buf;

    s->pos = s->buffer_size = buf_size;

    s->buf_end = s->buf_ptr + buf_size;

    s->eof_reached = 0;

    s->must_flush = 0;

    return 0;

}

        av_free(buf);

    /* rewind. reuse probe buffer to avoid seeking */

    if ((ret = ff_rewind_with_probe_data(*pb, buf, pd.buf_size)) < 0)

        av_free(buf);

    return ret;