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libavformat
On a DVD, because you're not opening a file, you would tell the demuxer what you're going to send it in the stream – video size, pixel format, and maybe more. See av_dict_set() for setting attributes in an AVDictionary struct.
avformat_open_input() will scan the input until it finds out what it is. I think setting dict options would only apply though if you were passing rawvideo, and not something that was muxed already and had data about the stream.
