API changes, most recent first:
+2021-04-27 - xxxxxxxxxx - lavf yyyyyyyyy - avformat.h
+ Constified AVFormatContext.*_codec.
+
2021-04-27 - xxxxxxxxxx - lavf yyyyyyyyy - avformat.h
Constified the pointers to AVInputFormats and AVOutputFormats
in AVFormatContext, avformat_alloc_output_context2(),