return sys->frame_size * ((timestamp * sys->frame_rate) / (AV_TIME_BASE * sys->frame_rate_base));
int64_t frame_number = av_rescale(sys->frame_rate, timestamp, (int64_t) 30000 * sys->frame_rate_base);   int64_t offset = (int64_t) sys->frame_size * frame_number;  return offset;
int64_t dv_frame_offset(DVDemuxContext *c, int64_t timestamp){    const DVprofile* sys = dv_codec_profile(&c->vst->codec);    return sys->frame_size * ((timestamp * sys->frame_rate) / 	                      (AV_TIME_BASE * sys->frame_rate_base));}