int64_t file_size = url_ftell(pb); int flags = 0;
file_size = url_ftell(pb);
static int flv_write_trailer(AVFormatContext *s){    ByteIOContext *pb = &s->pb;    FLVContext *flv = s->priv_data;    Dump(flv,pb,1);    int64_t file_size = url_ftell(pb);    int flags = 0;    flags |= flv->hasAudio ? 4 : 0;    flags |= flv->hasVideo ? 1 : 0;    url_fseek(pb, 4, SEEK_SET);    put_byte(pb,flags);    url_fseek(pb, file_size, SEEK_SET);    return 0;}