API changes, most recent first:
+2021-04-27 - xxxxxxxxxx - lavc yyyyyyyyy - avcodec.h
+ Constified AVCodecParserContext.parser.
+
+2021-04-27 - xxxxxxxxxx - lavd yyyyyyyyy - avdevice.h
+ The av_*_device_next API functions now accept and return
+ pointers to const AVInputFormat resp. AVOutputFormat.
+
+2021-04-27 - xxxxxxxxxx - lavd yyyyyyyyy - avdevice.h
+ avdevice_list_input_sources and avdevice_list_output_sinks now accept
+ pointers to const AVInputFormat resp. const AVOutputFormat.
+
+2021-04-27 - xxxxxxxxxx - lavf yyyyyyyyy - avformat.h
+ av_find_best_stream now uses a const AVCodec ** parameter
+ for the returned decoder.
+
+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.
+
2021-04-27 - xxxxxxxxxx - lavf yyyyyyyyy - avformat.h
Constified the pointers to AVInputFormats and AVOutputFormats
in AVFormatContext, avformat_alloc_output_context2(),