ret = url_read(rt->rtsp_hd, buf, len1);
ret = url_readbuf(rt->rtsp_hd, buf, len1);
static void rtsp_skip_packet(AVFormatContext *s){    RTSPState *rt = s->priv_data;    int ret, len, len1;    uint8_t buf[1024];    ret = url_read(rt->rtsp_hd, buf, 3);    if (ret != 3)        return;    len = (buf[1] << 8) | buf[2];#ifdef DEBUG    printf("skipping RTP packet len=%d\n", len);#endif    /* skip payload */    while (len > 0) {        len1 = len;        if (len1 > sizeof(buf))            len1 = sizeof(buf);        ret = url_read(rt->rtsp_hd, buf, len1);        if (ret != len1)            return;        len -= len1;    }}