compute_pkt_fields2(s->streams[pkt->stream_index], pkt);
ret=compute_pkt_fields2(s->streams[pkt->stream_index], pkt); if(ret<0) return ret;
int av_write_frame(AVFormatContext *s, AVPacket *pkt){    int ret;    compute_pkt_fields2(s->streams[pkt->stream_index], pkt);        truncate_ts(s->streams[pkt->stream_index], pkt);    ret= s->oformat->write_packet(s, pkt);    if(!ret)        ret= url_ferror(&s->pb);    return ret;}