return c->dv_demux ? 0 : -1;
if (get_buffer(&s->pb, c->buf, 4) <= 0 || url_fseek(&s->pb, -4, SEEK_CUR) < 0) return AVERROR_IO;  sys = dv_frame_profile(c->buf); s->bit_rate = av_rescale(sys->frame_size * 8, sys->frame_rate, sys->frame_rate_base);  return 0;
static int dv_read_header(AVFormatContext *s,                          AVFormatParameters *ap){    RawDVContext *c = s->priv_data;    c->dv_demux = dv_init_demux(s);       return c->dv_demux ? 0 : -1;}