API changes, most recent first:
+2021-04-27 - xxxxxxxxxx - lavc yyyyyyyyy - codec.h
+ avcodec_find_encoder_by_name(), avcodec_find_encoder(),
+ avcodec_find_decoder_by_name() and avcodec_find_decoder()
+ now return a pointer to const AVCodec.
+
2021-04-27 - xxxxxxxxxx - lavf yyyyyyyyy - avformat.h
Constified AVFormatContext.*_codec.