AVStream.codecpar

Lots of people are opening issues and/or sending emails that contain:

Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.

Perhaps we should do that.

The warning comes from mux.c:300, called from avformat_init_output, called from avformat_write_header. It is looking at AVCodecContext.codec_type, seeing that it is set, and then issuing the warning.

My guess is that it is being set by avcodec_open2, as we are manually opening all of the streams before writing the container header. (Oops?) I'm not sure if that actually makes sense.