[mythtv] Option setting for ffmpeg encoding

[Peter Bennett]

Hi Jean-Yves

I have fixed almost all of the ffmpeg deprecated functions and 
structures. In the latest fix I changed a number of fields in 
AVCodecContext that were deprecated as fields and should be passed as 
options. One thing that is not too clear to me is that the options seem 
to be able to be passed in at least three different ways. Here are examples:

1. av_dict_set(&opts, "refcounted_frames", "1", 0);
      then pass &opts into last parameter of avcodec_open2
2. av_opt_set(ctx->priv_data, "profile", "baseline", 0);
3. av_opt_set_int(ctx, "direct-pred", 1, 0);

Are these three equivalent? Should I use ctx or ctx->priv_data when 
using av_opt_set? All of these seem to have been used.

You can see what I have done with them in the last patch in the ticket 
(https://code.mythtv.org/trac/ticket/13186)

Regards
Peter