AVCodecParameters *par = ffvideo[stream]->st->codecpar;
AVRational dar;
AVRational sar = av_guess_sample_aspect_ratio(fmt_ctx, strm, NULL);
AVCodecParameters *par = ffvideo[stream]->st->codecpar;
AVRational dar;
AVRational sar = av_guess_sample_aspect_ratio(fmt_ctx, strm, NULL);